NAME

TEACHER

Chemistry
 What You Need to Know for Moles & Stoichiometry
Content Objectives
• Match the elements of compounds with the symbols of their atoms & ions
• Write compound formulas using symbols and valences of atoms and ions
• Select the number of atoms and ions in a compound from the given formula
• Name a given compound according to its given formula
• Compare the differences between an empirical formula and a molecular formula.
• Solve for the empirical formula based on the molecular formula; visa-versa
• Identify and write formulas of a binary compound
• Select and label products and reactants in a given chemical reaction
• Given the formulas for reactants and products, balance a chemical equation
• Deduce a missing reactant or product in a given chemical equation
• Correctly use the Law of Conservation
• Distinguish between the following
o Decomposition
o Double Replacement
o Single Replacement
o Synthesis

Key Subject Competencies

• Define stoichiometry
• Understand the concept of balance in chemical reactions
• Find the atomic mass of elements
• Use atomic mass to determine molecular mass and formula mass
• Define a Mole
• Determine mole from formula mass
• Calculate the percent composition by mass of each element in a compound or hydrate
• Name the four types of chemical reactions and give an example of each.
• Identify molecular formulas of substances
• Use molecular formulas to determine empirical formulas
• Use molecular formulas to represent structural formulas
• Define an empirical formula
• Determine which formulas are empirical
• Calculate the empirical formula of a substance from % composition
• Determine the molecular formula of a compound
• Distinguish between an empirical formula and a molecular formula
• Determine the empirical formula of any molecular formula

Vocabulary
• Moles • Molar Ratio • Double
• Formula Mass • Oxidation Number Replacement
• Synthesis • Coefficients • Single
• Stoichiometry • Molecular Formula Replacement
• Gram Formula • Yield • Molar Mass
Mass • Product • Empirical Formula
• Percent • Decomposition • Subscript
Composition • Reactant • Avogadro' s
• Hydrates • Polyatomic Number
 : Form WS5.3.1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

Chemical reactions are like mini-factories. Reactants go in,

and products come out. Chemical equations provide a
shorthand way to easily describe what occurs during a
chemical reaction. In a typical chemical equation, the
reactants are written on the left, while the products are
written on the right. The reactants and products are separated
by an arrow, or yield sign; which indicates that reactants
yield products. ( S^HESBI ~> lsKWHirH*sl ) There
are other symbols as well that show the state of the
chemicals involved in the reaction. They are: (s~) or 1 for a
solid precipitate; (0) for a liquid; (g) or ! for a gas; and (aq)
for dissolved in water or aqueous. Symbols can also be used
to show other factors involved in the reaction such as sources of energy used. These include: A for heat or tl for
light. These symbols are written above or below the yield sign because they are neither reactants nor products. The
complete equation shows the identity of the reactants and products using chemical formulas and symbols, the phases
of the reactants and products, any energy changes involved in the reaction, and the mole ratios of all the substances
indicated by the coefficients. Equations may occasionally be written omitting information about phases or energy
changes. The example below shows a complete chemical equation with all the components.

2KC1030)
A
In the above reaction, the equation shows that the reactant is solid potassium chlorate, the products are solid
potassium chloride and oxygen gas, manganese dioxide is a catalyst, and the reaction is endothermic. Symbols for
manganese dioxide and heat are shown above and below the yield sign because they are neither reactants nor
products.

For each of the chemical equations below, identify the reactants and the products, state what phase each is
in and state the mole ratios of all the products and reactants. See the sample below.

Reactants Products
Chemical Equation Ratio
Identity Phase Identity Phase
Sample:
' 2H2Cg) + 02(g)->2H20(«) H2 gas H20 liquid 2:1:2
02 gas

[A] 3Ca(NO3)2(a^) + 2Na3PO4(^) -+

6NaN03(ag) + Ca3(PO4)20)

-3-
 : Form WS5 . 3 . 1A Understanding Chemical Equations

CHEMICAL FORMULAS AND EQUATIONS

Reactauts Products
Chemical Equation Ratio
Identity Phase Identity Phase

[B] C02fe) + H20(0->H2C03(a?)

[C] ZnO) + 2HCl(a?) -*• ZnCl2(a?) + H2(g)

[D] CuO) + 2AgN03(a?) -*•

2Ag(» + Cu(N03)2(^)

[E] 2MgO) + 02(g) -> 2MgO(j)

[F] 2Fe(OH)2(j) + H202(a?) -^ 2Fe(OH)3(^)

[G] 3Cu(j) + 8HN03M ->

2NO(g) + 3Cu(N03)2(g) + 4H20(4)

[H] 2Li(j) + 2H20(e) ^ 2LiOHK) + H2fe)

[I] H20(e) + N205(g) -f 2HN03(*2)

[J] 2Al(^) + 3Zn(NO3)2(^)-»-

3Zn(j) + 2Al(N03)3(a?)

Evan P. Silberstein, 2002

-4-
 -: Form WS5 . 5 . 2A Name

CHEMICAL REACTIONS Date Period

During a chemical change, there is no change in mass. A

properly written chemical equation shows this. The equation
below is not properly written. It does not show conservation of
mass.

H +O H2O
32* 18 Yes
The reason the equation doesn't work is simple. There are two
atoms of oxygen in the reactants,, but only one in the product. If
two molecules of hydrogen react with a molecule of oxygen to
form two molecules of water, there are no atoms missing and
mass is conserved. The number of molecules is shown with a
number to the left of the formula known as a coefficient. A
coefficient behaves like a multiplier. It's not necessary to check
the mass to get a properly written equation. Counting atoms is
2(2)+ 32 = 2(18)
sufficient When the equation for the formation of water is written properly, 2H2 + 02 —>• 2H20; mere are 4 hydrogen atoms
and two oxygen atoms on both sides of the equation and the mass of the reactants is the same as the mass of the products.
Making the number of atoms equal on both sides of the equation is all that is needed. The process is called balancing.

Balance the equations below by writing the correct coefficient in the space before each formula. Coefficient
"1" need not be written.

i. Cl, HC1

2. Ca(NO,)-> + H,SOd CaSO4 + HNO,

3. Fe + Cl, -> IFeCl,

4. Fe+ O,-+ ' Fe

5. Zn + HC1 -> ZnCl2 + H

6. Cu + AgCH.COO _Cu(CH3COO)2 + Ag

7. H 9 SO A + NaOH-* a2SO4 + H2O

8. N9 + H, -> h ^3

9. CH d + O, -v CO,

10. s+ o?-» sc
Evan P. Silberstein, 2002

-5-
 Name

Rewrite and balance the equations below.

. N2 + H2 NH.

2. KC!0, KG! + (X

3. NaCi + F, NaF + CL

4. H2 + O2 -> H2O

5, AgNO, + MgCL -» -AgCl + MgCNOA

6. AIBr3 + .^^ 4 KBr + AI2(S04)3

*i
• /n-i

7. CH4 + O2 -> C02 + H20

8. C3H8 + O2 -» CO2 +' H2O.

pi
si 9, C8H]8 + 02 1O2 + H2O

10. FeCI3 + NaOH Fe(OH) + NaCI.

1L P + CX

12. Na + H2O NaOH +

13. Ag9O Ag + CX

14. Sn + O, SO,

15. CO2 + H20 0

16. K + MgBr, KBr + Mg

17. HCI + CaCO, CaCI2 + H2O + CO2.

Chemistry 1F8766 ©Instri Jctinnnl Fnir

 Name

Write the word equations below as chemical equations and balance,

1, zinc + lead (II) nitrate yield zinc nitrate + lead

2. aluminum bromide + chlorine yield aluminum chloride + bromine

3, sodium phosphate + calcium chloride yield calcium phosphate +

sodium chloride

4. potassium chlorate when heated yields potassium chloride + oxygen gas

5. aluminum + hydrochloric acid yield aluminum chloride + hydrogen gas

6, calcium hydroxide + phosphoric acid yield calcium.phosphate + water

7. copper + sulfuricacid yield copper (II) suifate + water + sulfur dioxide

8. hydrogen + nitrogen monoxide yield water + nitrogen

Chemistry IF8766 ©Instructional Fair, Inc.

 f. Form N5 . 5A Conservation of Mass

CHEMICAL FORMULAS AND EQUATIONS

Answer the questions below by circling the number of the correct response

1. If 46 g of X combines with 16 g of Yto form Z, how much Zis 10. In the equation 4AI + 302 -*• 2AI203, the number 4 is a
formed? (1)30g (2)2.9g (3)724g (4}62g (1) subscript, (2) oxidation state, (3) formula mass, (4) coefficient.

2. The formula mass of suite acid (H2S04) is (1) I94amu, (2}98 11. When the equation H2 + N2 -»NH3 is completely balanced using
amu, (3)50 amu, (4)192 amu smallest whole numbers, the sum of all the coefficients will be
(1)6(2)7(3)3(4)12
3. Which of the following equations does WOTshow conservation of
mass? (1) C + 02 -> C02 (2) Mg + S -+ MgS (3) H3 + S -+ H2S 12. When the equation H2 + Fe304 -*- Fe + H20 is completely
(4) H2 + 02 -+ H20 balanced using smallest whole numbers the coefficient of H2
would be (1)1 (2)2 (3)3 (4)4
4. If 6 g of hydrogen burns to produce 54 g of water, how much
oxygen was used? (1)48g (2)60g (3) 9 g (4)324g 13. When the equation C2H4 + 02 -» C02 + H20 is correctly balanced,
using smallest whole-numbered coefficients, the sum of all the
5. During a chemical change, the total mass (1) increases, coefficients is (1)16 (2)12 (3)8 (4)4
(2) decreases, (3) remains the same.
14. When the equation NH3 + 02 -+ HN03 + H20 is completely
6. Which of the following is NOT a balanced equation? balanced using smallest whole numbers, the coefficient of 02
(1) Cu + 2AgN03 -+ 2Ag + Cu(N03)a would be (1)1 (2)2 (3)3 {4)4
(2) 3BaCI2 * Fe2(S04)3 -» 2FeC!3 + SBaSO,,
(3) 4Na + 2H20 -*• 4NaOH + H; 15. When the equation C2H4 + 02 -4 C02 + H20 is balanced using
(4) 2KCI03 -+ 2KCI + 302 smallest whole numbers, what is the coefficient of the 02? (1) 1
( 2 ) 2 ( 3 ) 3 (4)4
Balance each of the equations below and write the SUM of the
coefficients in the appropriate place on the answer sheet. 16. When the equation Na(s) + H20(G) -^ NaOH(aq) + H2(g) is
correctly balanced using smallest whole numbers, the coefficient
7. Al + HCl -*- AICU + H, of the water is (1)1 (2)2 (3)3 (4)4

8. Li + H20 -*- LiOH * H2 17. When the equation Al(s) * 02(g) -*• AI203(s) is correctly balanced
using the smallest whole numbers, the coefficient of A!(s) is (1) 1
( 2 ) 2 ( 3 ) 3 (4)4

Evan P. Silberstein, 2003

 Form WS5 .1. 1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

Formula
Compounds are either ionic or molecular. The formulas for
ionic substances are always written with subscripts reduced to Finding the Formula Mass
lowest terms. This is because we know the ratio of ions in a
Find the formula mass of CuSO4
compound, but we don't necessarily know how many ions are
in a crystal of the compound. Formulas written in lowest terms StepJU Look up the mass of each element on
are called empirical formulas. Molecular substances can have the Periodic Table and round it off.
formul as that are not in lowest terms. For example, the formula Step 2: Multiply each element's atomic mass
of glucose is C6H12O6. All of the subscripts are divisible by six. by its subscript to get the product.
This is acceptable, however, because we know exactly how Step 3: Add the products together to get the
many atoms of each type are in a molecule of glucose. The total
formula for glucose is called a molecular formula and its mass
is called a molecular mass. Regardless of whether a compound Element Atomic Subscript Product
Mass
has a molecular formula or an empirical formula, the mass of
Cu 64 x 1 64
the compound is found the same way. The atomic masses of
. the elements in. the compound and the formula are used to S 32 ,, -t
32
determine the mass. The mass determined from the formula is x 4
0 36 64
called a formula mass. A molecular mass is a type of formula
mass. The terms are sometimes used interchangeably. Formula TOTAL 160
masses are determined by following the steps in the box to the
right. The results are in atomic mass units (amu).

Determine the formula masses of each of the substances below.

1. CaCl, 4. Ba3(P04)2

2. NH4OH 5. A12(C03)3

3. AgCH3COO 6. Zn(N03)2

Evan P. Silberstein, 2002

 GRAM FORMULA MASS Name

Determine the gram formula mass (the mass of one mole) of each compound below,

1. KMnO,4

2. KG!

3. Na2S04

4. Ca(NO3)2

5. AI2(S04)3

6- (NH4)3P04

7. CuSO,«5H2O

8. Mg3(P04)2

9. Zn(C2H302)2«2H20

10. Zn3(P04)2.4H20

11, H2CQ3

12,

13, Ba(CI03)2

14. Fe2(S03)3

15, NHdC2H302

i Chemistry 1F8766 . ' ' ©Instructional Fair, Inc.

 : Form WS5.6.1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

The rnole is a very useful concept in chemistry. It is a

quantity, just as a dozen is a quantity, but it is much more f Actually, the
than a dozen. The number of objects in a mole is 6.02 x 1023. word mole comes
from the word
The importance of the mole as a quantity in chemistry comes molecufe. It has
from the fact that all moles, just like all dozens, have the nothing to do with
you, so feel free, to
same number of particles. The actual number of particles is 'dig your way back
not that important. There is a much simpler way to know to wherever you
when you have a mole. A mole is a formula mass expressed s, ' came from! >
in grams. (1 mole = 1 gram formula mass)
Gram Formula
Substance Formula Mass
Mass
carbon I2amu 129
sodium chloride (NaCI) 58amu 58 g
glucose (CfiH1?0B) 180amu 180 g
Atomic mass units are too small to measure on a laboratory balance, but grams are not. An atom of carbon has a mass
of 12 amu and a molecule of glucose has a mass of 180 amu. Each mass represents one particle. Since the mass ratios
in formula masses and gram formula masses are the same (12 amu:180 amu::12g:180 g), the ratio of particles must
still be the same (Imoletl mole). If you think in dozens, this is easy to understand. If we compare the mass of 1 egg
to 1 elephant, it has the same mass ratio as 1 dozen eggs and 1 dozen elephants, because the ratio of objects is still 1
tol.

This is very useful for working with balanced equations. The equation for the formation
of ammonia, N2(g) + 3H2(g) ~+ 2NH3(g), tells us that 1 molecule of nitrogen combines
with 3 molecules of hydrogen to form 2 molecules of ammonia. This also means 1 mole mole
of nitrogen combines with 3 moles of hydrogen to form 2 moles of ammonia. The mole 2. g = G F M * mole
amounts can be measured in the laboratory. Of course, it helps to understand the (T

relationship between mass and moles. Based on the definition above, the gram formula 3. mole-
GFM
mass (GFM) is the number of grams in I mole. This results in the mathematical
relationships shown to the right.

-11-
 Name

Determine the number of moles in each of the quantities below.

, 25gofNaCi

2. 125gof HLSQ
2 - 4

3, 100, gof

4, 74 g of KC!

5, 35gofCuSO •5H2O

Determine the number of grams in each of the quantities below.

1. 2.5 moles of NaCI

2, 0.50 moles of H2SO4

3. T.70 moles of KMnO,

4. 0.25 moles of KC1

5. 3.2 moles of CuSO4»5H2O

Chemistry IF8766 tsilnstn intinnnl -Fnir. Inn

THE MOLE AND VOLUME Name

For gases at STP .(273 K and 1 atrn pressure), one mole occupies a volume of 22,4 L, What
volume wi.ll the following quantities of gases occupy at STP?

1, 1.00 mole of H2

2. 3.20 moles of O2

3. 0.750 mole of N2

4. 1,75 moles of CO2

5. 0.50 mole of NH3

6, 5.0gofri

7, 100, gof O,

8. 23.0 g of N,

9. 60. g of CO,

10; 10. gofNH,

Chemistry IF8766 '° " ©Instructional Fair, Inc

 Name

One mole of a substance contains Avogadro's Number (6.02 x 1023) of molecules.

How many.rnolecules are in the quantities below?

1. 2.0 moles

2. 1.5 moles

3. 0,75 mole

4. 15 moles

5. 0,35 mole

•How many moles are in the number of molecules below?

1. 6.02 xlO 2 3

2. 1.204X10 24

3. 1.5X10 2 0

4, 3,4 xlO 26

5. 7.5 xlO 1 9

Chemlstry IF8766 (^Instructional Fair. Inc.

 Name
MOLE-MOLE PROBLEMS
]. N — • 3H
^J I 1,-f 2NH,
4_ L 1 I 1*2

How many moles of hydrogen are needed to completely react with two moles
of nitrogen?

2. 2KCIO, 2KC1 + 3O,

How many moles of oxygen are produced by the decomposition of six moles
of potassium chlorate?

3. Zn + 2HC1 ZnC!*2 + H
' '2 • .
How many moles of hydrogen are produced from the reaction of three moles
of zinc with an excess of hydrochloric acid?

4, + 5OP2 3C0
-—— 2 4H20
How many moles of oxygen are necessary to react completely with four moles of
propane (C3H8)?

5. K3PO, + AI(N03)3 3KNO3 + AiPO4.

How many moles of potassium nitrate are produced when two moles of potassium
phosphate react with two moles of aluminum nitrate? ' -

Ohfirnistrv IFR7AA (Rilnetn i Pi-iir Ir

 : Form WS5 . 6 . 1A Working with Moles

CHEMICAL FORMULAS AND EQUATIONS

Calculate the mass of each of the following as illustrated in the example below:

Example
What is the mass of 2 moles of sodium thiosulfate?
g - GFM x moles
Na^ 23 x 2 = 46
S = 32 x 2 = 64 = 158«/mole x 2 mole
O = 16 x 3 =_48
158 = 316g

1. What is the mass of 3 moles of potassium nitrate 3. What is the mass of 3.5 moles of silver acetate
[KN03]? [AgCH3COO]?

2. What is the mass of 0.75 moles of aluminum oxide 4. What is the mass of 0.25 moles of calcium sulfate
[A1203]? [CaSOJ?

Calculate the number of moles for each of the following as illustrated in the example below:

Example
How many moles are in 390g of calcium chloride?

CaCI, moles =
Ca^ 40 x 1 ^ 4 0 GFM
Cl = 35 x 2 = 70 390
moles =
110 110

moles = 3.5 moles

5. How many moles are in 484.25 g of ammonium 7. How many moles are in 270. g of dinitrogen
phosphate [(NH4)3PO4]? pentoxide [N2O3]?

6. How many moles are in 75.46 g of sulfuric acid? 8. How many moles are in 546 g of tin IV fluoride
[SnF4]?

Evan P. Silberstein, 2002

-16-
 Form Ls5.4A Mo/e Concept
FORMULAS AND EQUATIONS

Answer the questions below by circling the number of the correct response

1. The gram molecular mass of C02 is the same as the gram 8. What is the total number of moles contained in115grams of
molecular mass of (1) CO (2) S02 (3) C2H6 (4) C3Ha C2HSOH?
(1)1.00 (3)3.00
2. The number of molecules in 1.0 mole of S02 is the same as the (2)1.50 (4)2.50
number of molecules in
(1) 1.0 mole of N2 (3) 0.25 mole of N02 9. How many moles of water are contained in 0.250 mole of
(2) 2.0 moles of Ne (4) 0.50 mole of NH3 CuS04-5H20?
(1)1.25 (3) 40.0
3. What is the gram formula mass of Ca(HC03)2? (2) 4.50 (4) 62.5
(1)101 (3) 202
(2) 162 (4) 324 10. Which represents the greatest mass of chlorine
(1) 1 mole of chlorine (2) 1 atom of chlorine
4. What is the total mass of iron in 1.0 mole of Fe203? (3) 1 gram of chlorine (4) 1 molecule of chlorine
(1)160g (3)72g
(2)112g (4)56g 11. What is the total mass of iron in 1.0 mole of Fe203?
(1)160g (3)72g
5. What is the mass, in grams, of 1.0 mole of (NH4)2S? (2}112g (4)56g
(1) 50 (3) 64
(2) 54 (4) 68 12. What is the mass, in grams, of 1.0 mole of (NH4)2S?
(1)50. (3)64
6. The mass of two moles of sulfuric acid, expressed in grams, is (2) 54 (4) 68
equal to
13. What is the gram atomic mass of the element chlorine?
,.M 9S ,ot 6 - 02x 1C}23
d) — (3) (1)17g (3)52g
2 (2)35g (4}70.g
(2)2x )8 (4)2x(6.02X10 2 3 )
14. The mass in grams of 1.00 mole of CaS04'2H30 is
7. Which quantity is equivalent to 39 grams of LiF?
(1)172g (3)136g
(1)1.0 mole (3) 0.30 mole (2)154g (4)118g
(2) 2.0 moles (4) 1.5 moles

Evan P. Silberstein, 2003

-17-
 : Form WS5.7.1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

Calculations based on quantitative relationships in a balanced chemical

equation are called stoichiometry. Stoichiometric calculations are based on
several assumptions. It is assumed that the reaction has no side reactions, the
reaction goes to completion, and the reactants are completely consumed. One
type of problem that can be solved stoichiometrically is based on the mole
ratios of a balanced equation. A sample problem is shown below.

/ ~ ~
Sample Problem
How many moles of oxygen are consumed when 0.6 moles of hydrogen
burns to produce water?
2 H,(g) + 0,fe) -+ 2
Step 1: Write a balanced equation and
determine the mole ratios from mole 2 1 2
the equation ratio

known unknown
Step 2: Identify the known and the moles
0.6 X
unknown

Step 3: Set up a proportion and solve 2 1

for the unknown Q.6mol x
2x — 0.6mol

Answer the questions below using the procedure described in the sample problem above.

1. How many moles of oxygen will be produced from the decomposition of 3 moles of KC103?

KC10, KC1

2. How many moles of Zn will be needed to completely react with 0.4 moles of HC1?

Zn + HC1 ZnCl, H,

-18-
 Form WS5 . 7 . 1A Stochiometric Relationships

CHEMICAL FORMULAS AND EQUATIONS

3. How many moles of oxygen will be needed to completely oxidize 4 moles of CH4?

_02 -> _CO 2 + _H20

4. How many moles of hydrogen will be needed to react with 2 moles of nitrogen according to the following?

_N2 + _H2 -»• __NH3

5. Using the above reaction how many moles ofNH 3 will be formed if 18 moles of H2 is used?

6. How many moles of sulfur will be needed to oxidize 3 moles of zinc to zinc sulfide?

Zn + S -> ZnS

7. How many moles of silver chloride will be produced if 2 moles of silver is allowed to react with an
unlimited amount of chlorine?

^Ag + + _C1- -+ _AgCl(s)

Evan P. Silberstein, 2002

-19-
MIXED MOLE PROBLEMS Name

Solve the following problems,

1. How many grams are there' in 1,5 x 1025 molecules of CO2?

2. What volume would the CO, in Problem 1 occupy at STP?

3. A sample.of NH gas occupies 75.0 liters at STP. .How many molecules is this?

4. What is the mass of the sample of NH. in Problem 3?

5. How many atoms are there in 1.3 x 1022 molecules of NO2?

6. A 5.0 g sample of O9 is in a container at STP. What volume is the container?

7. How many molecules of O2 are in the container in Problem 6? How many atoms
of oxygen? -

Chemistry IF8766 " ©Instructional Fair. Inc.

 : Form WS5.1.3A Name

CHEMICAL FORMULAS and EQUATIONS Date Period

Percentage composition is determined by finding the Sample Troblem; Find the percentage composition of MgC03
formula mass of a compound, multiplying the mass of
each element by 100, and dividing the product by the Formula Mass Percentage Composition
formula mass of the compound. Use the periodic table Mg = 24 x 1 = 24 %Mg = 24 * 100 = 29
to find the masses of individual elements. See the C = 12 x 1 = 12 %C = 12 x 100 -14
Sample Problem to the right. 0 = 16 x 3 = %0 = 48 x 100

1. What is the percentage composition of: Na, 0, and H in the compound NaOH?

Na

2. Calculate the percentage composition_of baking soda (NaHC03).

Na

3. Calculate the percentage of each of the elements within acetic acid (HC2H302), the substance found in vinegar.

H ., O

4. What is the percentage composition of a soap (C17H35COONa)?

C _, H.

5. Which of the following has the highest percentage of nitrogen? (•)

Ca(N03); (NH4)2S04.

-21-
 : Form WS5 .1. 3A

CHEMICAL FORMULAS and EQUATIONS

Percentages can refer to different portions of a Sample "Problem: What is the percentage of water in CuSCy 5H20?
compound. In hydrated crystals, for example, it
is possible to calculate the percentage of water. Formula Mass of CuSOA Formula Mass of H,0
Find the formula mass of each portion of the Cu = 64 x 1 = 64 H = 1 x 2 ^ 2 ^
compound separately. Add them together to get S = 32 x 1 = 32 0 = 16 x 1 = 16
the mass of the compound. Then multiply the 0 = 16 x 4 = J34 18
mass of the water by 100, and divide the 160 Mass of Water: 5 x 18 = 90 TOTAL: 160 + 90 =250

product by the formula mass of the compound. Percentage

See the Sample Problem to the right. UoH20^ 90 x 100 - 250 = 3 6 % ,

6. Calculate the percentage of water in the compound CaS04'6H2O.

7. Calculate the percentage of water in the compound CaCl2-10H2O.

Once you know the percentage composition of Sample'Problem: A 40.0 g sample of CaCI2'2H?0 is heated to dryness. What is the
a compound, you can figure out the mass of any mass of the remaining calcium chloride,
component of the compound in a sample of any
mass simply by multiplying the sample mass by Formula Mass of CuSO, Formula Mass of H-,0
the percentage. See the Sample Problem to the Ca^ 40 x 1 = 40 H = 1 x 2 = 2
right. Cl = 35 x 2 = 22 0 = 16 x 1 = _16
0 = 16 x 4 = 110 18

8. How many milligrams of iron are Mass of Water: 2 x 1 8 ^ TOTAL: 36^146

delivered from a 250. mg tablet of Percentage
FeSCy7H2O? ^ 110 x 100 •*• 146 = 75%

Mass
0.75 x 40.0 g = 30, g

9. What is the yield of uranium from 2.50 kg U308?

EvanP.SiIberstein,2005

-22-
 PERCENTAGE COMPOSITION Name

Determine the percentage composition of each of the compounds below.

1. KMnO4
. K -
' Mn =
O -
"li-
2. HCI
H =
Ci -

3. Mg(N03)2
Mg = _
'
:«fj
N = __
O -
I
I
4, (NH4)3P04
N =
H =
p =

O -

5. AI2(SOd)3
Al -
O _-.

O =

Solve the following problems, -

6. How many grams of oxygen can be produced from the decomposition of 100. g
of KCIO3?
7. How much iron can be recovered from 25.0 g of Fe2O3?
8. How much silver can'be produced from 125gof Ag2S?

Chemistry IF8766 ©Inslructfnnn!

Name GFM, Balancing & % Composition Date
Ms. Tintella Practice Regents Chemistry

1. What is the gram-formula mass of Ca3(PO4)2 ? 8. Given the unbalanced equation:

A) 248 g/mol B) 263 g/mol
<s) -> _MgCb(s)+__O2(g)
C) 279 g/mol D) 310. g/mol
2. The gram formula mass of NH4C1 is What is the coefficient of 02 when the equation is
balanced correctly using the smallest whole
A) 22.4 g/mole B) 28.0 g/mole
number coefficients?
C) 53.5 g/mole D) 95.5 g/mole
A) 1 B) 2 • C) 3 D) 4
3. The gram-formula mass of (NHVhCCb is
9. Which equation is correctly balanced?
A) 46.0 g B) 64.0 g
C) 78.0 g D) 96.0 g A) H2 + 02 ^ H20
4. What is the gram formula mass of CuSCU- 5I-hO? B) Ca + Ch-»CaCl
C) 2H2 + 02-»2H 2 O
A) 160. g B) 178 g
C) 186g D) 250. g
10. Given the unbalanced equation:
5. Given the unbalanced equation:
Al + CuS04 ->• Ak(S04)3 + Cu
3 + __Ca(OH> -» __A1(OH)3 +
_CaS04 When the equation is balanced using the smallest
whole-number coefficients, what is the
When the equation is correctly balanced with the coefficient of Al?
smallest whole-number coefficients, the sum of the A) 1 B) 2 C) 3 D) 4
coefficients is
11. What is the percent composition by mass of
A) 5 B) 7 C) 8 D) 9 hydrogen in NHiHCOs (gram-formula mass ~ 79
6. A balanced equation representing a chemical grams/mole)?
reaction can be written using A) 5.1% B) 6.3%
A) chemical formulas and mass numbers C) 10.% D) 50.%
B) chemical formulas and coefficients 12. What is the percent composition by mass of
C) first ionization energies and mass numbers nitrogen in NHUNOa (gram-formula mass = 80.0
D) first ionization energies and coefficients grams/mole)?
7. Which chemical equation is correctly balanced? A) 17.5% B) 35.0%
C) 52.5% D) 60.0%
13. What is the percent composition by mass of
C) 2NaCl(s) -» Na(s) + Clife) aluminum in Ah(SO4)3
(gram-formula mass = 342 grams/mole)?
D) 2KCl(s) ->- 2K(s) + Ch(g)
A) 7.89% B) 15.8%
C) 20.8% D) 36.0%
14. The percent by mass of hydrogen in NHs is equal
to

A) —
1 xv B) -3- x C) ir x D) 17 x
100 100 100 100

-24-
 GFM, Balancing & % Composition

15. What is the percent by mass of oxygen in Ca(OH)

2
[formula mass — 47.1]
A) 21.6% B) 43.2%
C) 45.9% D) 54.1%

-25-
 : Form WS5 .1. 2A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

The chemical formula for a molecular compound shows the number

and type of atoms present in a molecule. Ionic crystals are a e too, pipsquea
collections of ions. The chemical formula for an ionic compound
but 1 have more sodium an
chioride ions than you
shows the ratio ions in the compound. The ratio of ions in the
formula for an ionic compound is always in lowest terms. A
chemical formula in which the ratio of the elements are in lowest
terms is called an empirical formula. For example, the formula for
table salt, sodium chloride, is NaCl even though a salt crystal may
have millions of ions and millions of ionic bonds. A glucose,
molecule (C6H12O6) such as the one pictured
to the left, on the other hand, has exactly six
carbon atoms, twelve hydrogen atoms, and
six oxygen atoms per molecule. The
molecular formula for glucose is not an
empirical formula. All the subscripts are divisible by six. When the subscripts are divided
by six, the empirical formula for glucose, CH2O, is obtained. Some molecular formulas,
such as the one for carbon dioxide, C02, are already empirical formulas without being
reduced.
There are two skills you need to learn in order to work with empirical formulas. They
are finding the empirical formula from the molecular formula and Finding the molecular
formula from the empirical formula and the molecular mass:

* to find the empirical formula from the molecular formula

( divide all the subscripts by the greatest common factor J|

Determine the empirical formula, for each of the following molecular formulas.

1. C8H!8 6. H20 „___ __

2. H202 _________^_^_ 7. C4H8

3- Hg2Cl2 8. C4H6

4. C3H603 9. C7H12

5. Na2C204 . . . . 10. CH3COOH ..

NEXT PAGE
 : Form WS5 .1. 2A Empirical Formulas

CHEMICAL FORMULAS AND EQUATIONS

to find the molecular formula from the empirical formula and the molecular mass.
^ N
Step 1: Determine the empirical formula mass.
Step 2: Divide the molecular mass by the empirical
formula mass to determine the multiple..
Step 3: Multiply the empirical formula by the by the
multiple to find the molecular formula

Sample Problem
A compound with an empirical formula of CH2O has a molecular mass of 90 amu. What is its
molecular formula?

Step 1: Determine the empirical formula mass.

_CH2O_
C = 1 2 x 1 «12
H= 1 x 2 « 2
O ^ 1 6 x l =16
30
Step 2: Divide the molecular mass by the empirical formula mass to determine the multiple,
90 „ Q
30
Step 3: Multiply the empirical formula by the by the multiple to find the molecular formula
[CH20] x 3 - C3H603

Determine the molecular formula for each of the following:

11. Find the molecular formula for a compound with a mass of 78 amu and the empirical formula CH.

12. Find the molecular formula for a compound with a mass of 82 amu and the empirical formula C3H5.

13. Find the molecular formula for a compound with a mass of 90 amu and the empirical formula HC02.

14. Find the molecular formula for a compound with a mass of 112 amu and the empirical formula CH2_

15. Find the molecular formula for a compound with a mass of 40 amu and the empirical formula C3H4.

© Evan P. Silberstein, 2002

-27-
Name

Classwork Review Activity

Show your work

Ti2(Cr207)3

1. Name the compound

2. State the type of bond or bonds is in this compound

3. Give the number of moles of oxygen in the compound

4. Give the number of moles of atoms in the compound

5. Give the Gram Formulas Mass of the compound

6. Give the number of moles of oxygen in the compound

7. Give the percent by mass of oxygen in the compound

-28-
 Name

Classwork Review Activity

Show your work

Fe2(S203)3

1. Name the compound

2. State the type of bond or bonds is in this compound

3. Give the Gram Formulas Mass of the compound

f
4. Give the number of moles of sulfer in the compound

5. Give the number of moles of atoms in the compound

6. Give the number of moles in 75 grams of the compound

7. Give the percent by mass of oxygen in the compound

-29-
 Name
EMPIRICAL FORMULAS
What is the empirical formula (lowest whole number ratio) of the compounds below?

1. 75% carbon, 25% hydrogen

2, 52.7% potassium, 47,3% chlorine

3, 22,1% aluminum, 25,4% phosphorus, 52.5% oxygen

4. 13% magnesium, 87% bromine

5, 32.4% sodium, 22.5% sulfur, 45.1% oxygen

6, 25.3% copper, 12.9% sulfur, 25,7% oxygen, 36.1% water

j ' Chemistry IF8766 -30- ©Instrucfional Fair, Inc.

) .'•'.
DETERMINING MOLECULAR Name
FORMULAS (TRUE FORMULAS)
Solve the problems below.

1. The empirical formula of a compound is NO2, Its molecular mass is 92 g/mol.

What is its molecular formula?

2, The empirical formula of a compound is CH2. Its molecular mass is 70 g/mol.

What is its molecular formula?

3, A compound is found to be"40.0% carbon', 6.7% hydrogen and 53,5% oxygen,

its molecular mass is 60. g/mol. What is its molecular formula?

4. A compound is 64.9% carbon, 13,5% hydrogen and 21.6% oxygen, its molecular
mass is 74 g/mol. What is its molecular formula?

5. A compound is 54.5% carbon, 9,1% hydrogen and 36.4% oxygen. Its molecular
/mass is 88 g/mol. What is its molecular formula?

Chemistry IF8766 -31- ©Instructional Fair, inc

 : Form LsS.lA Analyzing Chemical Formulas

CHEMICAL FORMULAS AND EQUATIONS

Answer the questions below by circling the number of the correct response

1. An example of an empirical formula is (1) C2H2, (2)H202, 17. The empirical formula of a compound is CH4. The molecular
(3) C2CI2I (4) CaCI2 formula of the compound could be (1) CH4, (2) C2H6, (3) C3HS,
(4)C4H10
2. A 10.0 gram sample of a hydrate was heated until all the water of
hydration was driven off. The mass of anhydrous product 18. A hydrocarbon has the empirical formula CH3. The most probable
remaining was 8.00 grams What is the percent of water in the molecular formula for this compound is (1) CH3, (2) C2H6,
hydrate? (1)12.5% (2)20.0% (3)25,0% (4)80.0% (3)C 3 H B ,(4)C 4 H 6

3. A compound has the empirical formula N02. Its molecular formula 19. A compound with an empirical formula of CH2 has a molecular
could be (1) N02, (2) N20, (3) N402, (4) N404. mass of 70. What is the molecular formula? (1) CH2 (2) C2H4
(3)C 4 H 8 (4)C S H 10
4. The percent by mass of oxygen in Ca(OH)2 (formula mass = 74) is
closest to (1)16, (2) 22, (3) 43, (4) 74. 20. What is the percent by mass of oxygen in CH3OH? (1)50.0
(2)44.4 (3)32.0 (4)16.0
5. The empirical formula of a compound is CH. Its molecular mass
could be (1)21, (2) 40, (3) 51 ,(4) 78. 21. The approximate percent by mass of potassium in KHC03 is
(1)19%, (2) 24%, (3) 39%, (4) 61%
6. What is the percent by mass of oxygen in NaOH (formula mass =
40.)? (1)80. (2)40. (3)32 (4)16 22. A compound has an empirical formula of CH2 and a molecular
mass of 56. What is its molecular formula?
7. A compound whose empirical formula is CH20 could be (1)CH2 (3)C3Ha
(1) HCOOH, (2) CH3OH, (3) CH3COOH, (4) CH3CH2OH. (2)C2H4 (4)C4He

8. The percent by mass of oxygen in CO is approximately (1)73%, 23. What is the percent by mass of hydrogen in CH3COOH (formula
(2)57%, (3)43%, (4)17%. mass = 60.)?
(1)1.7% (3)6.7%
9. A compound has an empirical formula of CH2 and a molecular (2)5.0% (4)7.1%
mass of 56, Its molecular formula is (1}C2H4, (2) C3H6, (3) C4H8,
(4) C5H10. 24. What is the percentage by mass of oxygen in CuO?
(1)16% (3)25%
10. What is the percent by mass of hydrogen in NH3 (formula mass = (2) 20% (4) 50%
17.0)? (1) 5.9% (2) 17.6% (3) 21.4% (4) 82.4%
25. What is the approximate percent composition by mass of CaBr2
11. The empirical formula of a compound is CH2 and its molecular (formula mass = 200)? (1) 20% calcium and 80% bromine
mass is 70. What is the molecular formula of the compound? (2) 25% calcium and 75% bromine (3) 30% calcium and 70%
(1)C 2 H 2 (2)C 2 H 4 (3)C 4 H 1D (4)C 5 H 10 bromine (4) 35% calcium and 65% bromine

12. The percent by mass of nitrogen in Mg(CN)2 is equal to 26. A 60. gram sample of LJOH20 is heated in an open crucible until
(1) 14/76 x 100, (2) % x 100, (3)28/76 x 100, (4) % x 100. all of the water has been driven off. What is the total mass of LiCI
remaining in the crucible?
13. What is the percent by mass of oxygen in Fe203 (formula mass = 0)18g. (3)42g.
160)? (1)16% (2)30.% (3)56% (4)70.% (2)24g. (4)60g.

14. Which formulas could representthe empirical formula and the 27. Which compound contains the greatest percentage of oxygen by
molecular formula of a given compound? (1) CH20, C4H604 mass?
(2) CHO CeH1206 (3) CH4, C3H12 (4) CH2, C3H6 (1) BaO (3) MgO
(2) CaO (4) SrO
15. The percent by mass of carbon in C03 is equal to (1}'14/12X 100,
(2)Xx100,(3) 2 % 2 x100,(4) 1 2 / 2 B x10Q 28. The precent by mass of oxygen in MgO (formula mass = 40) is
closest to
16. The percentage by mass of hydrogen in NH3 is equal to (1)16% (3)40%
(1) V)7 x 100 (2) 3/17 x 100 (3) 17/3 x 100 (4) B/17 x 100 (2) 24% (4) 60%

© Evan P. Silberstein, 2002

-32-
 : Form WS5 . 4 . 1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

Chemical reactions can be grouped into four basic types. They

are direct combination or synthesis, decomposition, single Patterns of the Reaction Types
replacement or substitution, and double replacement or
exchange of ions.
An example of synthesis is shown below: Legend:
catalyst > A and C = metals
* ->2NH
' 3 (g) '>• B and D = nonmetals
A
__ + ^
Synthesis often results in the formation of only one product
Direct combination (synthesis)
from two reactants, but not always. Combustion, as in the
A + B->AB or
following example, CH4(g) +202(g) -> C02(g) + 2H2O, is also
AB + D-+AD + BD
a form of synthesis because the oxygen combines with both the
Decomposition
metal and the nonmetal to form two oxides.
AB-^A + B
Decomposition is the reverse of synthesis. One reactant
Single Replacement (substitution)
breaks apart to form several products. This is what happens
AB + C -+ CB + A or
when hydrogen peroxide decomposes over time to leave
AB + D -t- AD + B
behind plain, ordinary water [2H202(a^) -+ 2H20(£) + 02fe)].
Double Replacement (Exchange of Ions)
During a single replacement reaction, a more active metal
AB + CD -* AD + CB
replaces a less active metal in a compound, or a more active
nonmetal replaces a less active nonmetal in a compound. This is
what happens when a metal becomes corroded by an acid
s) + 6HC\(aq) —> 2FeCl3(fl#) + 3H2(g)]. In single replacement reactions, an element is reacting with a compound.
Double replacement reactions occur between aqueous compounds. The cations and anions switch partners. If
an insoluble precipitate forms, the reaction is an end reaction, otherwise the result is an aqueous mixture of ions.
An example of a double replacement reaction is AgN03(ag) + NaCl(<z#) — *• NaN03(agr) + AgCl(j).

For each of the reactions shown below, identify the type of reaction.

PbI2(j)

2. ^) + Cu(j)

3. Fe(OH)3(j) +

4. 2MgO) + 02(g)
5. H2C03(a?) -> H20({)
6.

7. Br2(G)

8. 2KC103C?)

9. 2K(j) + 2H20(fi)

Evan P. Silberstein, 2002

 : Form WS5.5. 3A - • Name

CHEMICAL FORMULAS and EQUATIONS Date Period

Balance the equations below by writing coefficients greater than one in front
of the formulas where needed. Identify the reaction type in the answer space
to the left of the equation [Synthesis (S) r Decomposition (D) f Single
Replacement (SR)f or Double Replacement (DR) ] .

_____ 1. Al + HC1 -+ A1C13 + H2T

2. Fe203 + C -> Fe + C0 2 I

3. S(s) + 0 2 ( g ) -+ S03(g)

4. N2 + H 2 -* NH 3

5. H20 + P 2 0 5 -^ H 3 P0 4

6. NH 4 NO 2 —-^ H20 + N2t

A

7. Ba(N03)2 + F e 2 ( S 0 4 ) 3 ->• BaS0 4 I + Fe (NO 3 )

8. ZnCl 2 + AgN0 3 -^ Zn(NO3)2 + AgClI

9. Na 2 0 + H 2 0 -^ NaOH

10. NiC0 3 + A 1 ( O H ) 3 -^ Ni(OH)2 + A12(C03)3

11. Ca(C103)2 > CaCl 2 + 02t

A

12. Mg + H 2 0 "> Mg(OH)2 + H2t

© Evan P. Silberstein, 2002

-34-
 CLASSIFICATION OF Name
CHEMICAL REACTIONS
Classify the reactions below as synthesis, decomposition, single replacement (cationic or
anlonlc) or double replacement.

, 2H2 + 02 -> 2H20

2. 2H2O -» 2H2 + O2

i
!*
W
f?s;
3, Z n - + H2SO4 -> ZnS04 + H2

ft
||| 4, 2CO + 02 -> 2C02

5, 2HgO -» 2Hg '+ O,

'If 4
'iSr
li
6, 2KBr + C!2 -> 2KCI + Br2

7. -CaO + H2O -> Ca(OH)2

8. AgNO, + NaCI -> AgCI + NaNO,

9, 2H202 -* 2H20 + 02

10, Ca(OH), + (-LSCT

r\ ' IQ ^~^ J -* CaSC> + 2H,O
^^^ **^X^ ^-^ ^ ' *— J 'O

Chemistry IF8766 °°" • ©Instructional Fair, Inc

 : Form WS5.5.4A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

A chemical equation contains a lot of information. Many equations show evidence of a chemical change such as
a change in temperature (exothermic — give off heat; endotherrnic — absorb heat), release of a gas, or formation of
aprecipitate. Other identifying characteristics of a chemical equation such as a change in color or a change in odor
cannot be demonstrated in the equation. Some changes and/or conditions are shown using symbols such as [1] solid
precipitate - (Y) or I; [2] liquid - (T); [3] gas - (g) or 1; [4] dissolved in water or aqueous - (aq}; [5] heat ~ A;
[6] electricity — elec.; and [7] light — T I. Symbols and formulas that are neither reactants nor products are written
above or below the yield sign (—>•). Examine the equation below:
MnO2(.r)
2KC1O3(Y)
A
The equation tells us the following: [1] The reactant is KC103; [2] KC103 is a solid; [3] KC103 decomposes,
particularly when heated (A) in the presence of the catalyst MnO2; [4] One of the products is KCI, a solid; [5] The
other product is O2, a gas. [6] Conservation of mass is shown because the reactants contain 2 atoms of K, 2 atoms
of CI, and 6 atoms of 0, and the products contain 2 atoms of K, 2 atoms of Cl, and 6 atoms of 0 also.
Sometimes a reaction results in the formation of a precipitate from dissolved reactants. Examine the equation
below:
Ca(N03)2(a?) -+ 2KNO3(a?) + CaS04(s)

The equation tells us the following: [1] The reactants are K2S04 and CaN03; [2] Both reactants are dissolved; [3] A
double -displacement reaction occurs resulting in the formation of a precipitate; [4] The precipitate is identified
using Table F- Solubility Guidelines; [5] Conservation of mass is shown because the reactants contain 2 atoms of
K, 1 sulfate ion, 1 atom of Ca, and 2 nitrate ions, and the products contain 2 atoms of K, 1 sulfate ion, 1 atom of
Ca, and 2 nitrate ions; [6] The sum of the coefficients is 5 as in the example below.

Example
Unbalanced Equation: CuS04 + AgN03 -+ Cu(NQ3)2 + Ag2S04
Balanced Equation: CuS04 + 2A gN0 3 -> Cu(N03)2 + Ag2S04
Sura of the Coefficients: 1 + 2 + 1 + 1 = 5
mamaot

Examine the unbalanced equations in the table on the next page. Determine the following: [1] The sum of
the coefficients of the balanced equation; [2] The type of reaction (direct combination, decomposition, single
displacement, double displacement}-., [3] Identify the phase(s) of the product(s); and [4] The signs that a
chemical change has occurred.

Go on to the next page.

-36-
 f: Form Ls5 . 3A Describing Reactions Using Chemical Equations
CHEMICAL FORMULAS AND EQUATIONS

Answer the questions below by circling the number of the correct response

1. The symbol (aq) after a chemical formula means (1}solidor

precipitate, (2) liquid, (3) gas, (4) aqueous or dissolved.

2. In the reaction, AgN03 + NaCI -+ AgCI + NaN03, the reactants

are (1) AgCI and NaN03l (2) AgN03 and NaCI, (3) Ag and Na,
(4) Cl and N03.

3. In the reaction, AgN03 + NaCI -»• AgCI + NaN03, which of the four
substances involved is a precipitate? [HINT: Refer to Chad C]
(1) AgNC-3 (2) NaCI (3) AgCI (4) NaN03

Answer questions 4-5 by referring to the equation below:

2KCI03(s) —--> 2KCI(s} * 302fe)

4, The symbol A under the yield sign indicates that (1) the reaction
is exothermic, (2) the reaction is endothermic, (3) a solid
precipitate forms, (4) heat is a product of the reaction.

5, Mn02fs) is written above the yield sign because Mn02(s) is (1) a

reactant, (2) a product, (3) neither a reactant nor a product,
(4) both a reactant and a product.

Evan P. Silberstein, 2003

-37-
 : Form WS5 . 5 . 4A Everything about Equations

CHEMICAL FORMULAS AND EQUATIONS

Sum of the
Unbalanced Equation Reaction Type Phase Evidence of Chemical Change
Coefficients

1 . FeCl3(ag) + NaOH(ag) -> NaCl(?) + Fe(OH)3(?)

2. Al(j) + HCl(a?)-^AlCl 3 (?) + H2(?)

3. Mg(j) + 0 2 Cg)^MgO(?)

'1 H O (nr\7 , o p/3\. r) f?\. H2C03(ag) -> H2O(?) + C02(?)

6. PfaO) 4- CuSO4(G5) ^ PbS04(?) + Cu(?)

7. H20(e)+N205fe)^HN03(?)

8. Na(s)+H 2 0((9->NaOH(?) + H2(?)

9. K2Cr04(ag) + Al(N03)3(ag) -» KNO3(?) + Al2(Cr04)3(?)

] 0. NaOH(ag) 4- H2S04(a?) -+ Na2SO4(?) + H2O(?)

' I . C2H6fe) + 0 2 ( i g)->CO,(?)4H 2 0(?)

12. GU(J) + AgN03(of7) -> Cu(N03)2(?) + Ag(P)

13. Nafe) + 0 2 Cg)^NAC?)

- °3fe) t| * O2fe)

15. Ca(C103)2(Gg) + Li2SO4(^) -+ CaSO4(?) + LiClO3(?)

Evan P. Silberstein 3 2002

 : Form Ls5 . 4A Types of Reactions

CHEMICAL FORMULAS AND EQUATIONS

For each of the reactions described in questions 1-7, write the

correct number to indicate whether the reaction type is
(1) DECOMPOSITION, (2) DIRECT COMBINATION, (3) SINGLE
REPLACEMENT, or (4) DOUBLE REPLACEMENT

1. A reaction occurs in which only one reactant is present.

2. A metal reacts with an acid. (2Fe + 6HCI -t- 2FeCI3 + 3Hj)

3. Magnesium burns,

4. Two salt solutions react with each other.

5. Two elements unite to form a compound,

6. A compound breaks down.

7. HCI + NaOH-> NaCI +H20

8. Many sulfide ores are prepared for refinement by roasting. This

reaction can BEST be described as (1) decomposition, (2) direct
combination, (3) single displacement, (4) double displacement.

9. During smelting, oxide ores are reduced to pure metais by

reacting with (1) oxygen, (2) hydrogen, () carbon, (4) nitrogen.

Evan P. Silberstein, 2003

-39-
 Name
COMPOSITION OF HYDRATES
A hydrate is an ionic compound with water molecules looseiy bonded to its crystal
structure. The water is in a specific ratio to each formula unit of the salt. For example, the
formula CuSO4»5H20 indicates that there are five-water molecules for every one formula
unit of CuSO4. Answer the questions below.

1, What percentage of water is found in CuSO «5H 0?

2, What percentage of water is found in Na S»9H20?

3. A 5.0 g sample of a hydrate of BaCI2 was heated, and only 4.3 g of the anhydrous
salt remained. What percentage of'water was in the hydrate?

4. A 2.5 g sample of a hydrate of Ca(NO3)2 was heated, and only 1.7 g of the
anhydrous salt remained. What percentage of water was in the hydrate?

5, A 3,0 g sample of Na2CO3«H20 is heated to constant mass. How much anhydrous

salt remains?

6. A 5.0' g sample of Cu(NO3)2«nH20 is heated, and 3.9 g of the anhydrous salt remains,
What is the value of n?

Chemistry IF3766 ©Instrurrfinnnl

 : Form WS5 . 5 . 1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

During a chemical reaction, new substances form with new properties. This
means that during a chemical reaction there are both chemical changes and
physical changes. Physical changes such as the formation of a solid
precipitate, a liquid, or a gas, provide evidence that a chemical change has
occurred. During a chemical change, the atoms of the reactants are
rearranged to form new substances or products. No new atoms are created
and none of the original atoms are destroyed. As a result, the mass of the AFTER
reactants and the products is the same. This is called conservation of mass.
When water (H2O) forms from hydrogen (H2) and oxygen (O2), for example,
the hydrogen and oxygen atoms are rearranged to form the new substance,
but no new atoms are created and none of the original atoms are lost.
Chemical reactions are described by chemical equations which show the
reactants, the products, and conservation of mass.

Answer the questions below based on the reading above, your knowledge of chemistry, and the information
provided below.

A student poured silver nitrate solution into a

flask and put sodium chloride solution in a Sodium Chloride Solution

medicine dropper. Then the student put the Silver Nitrate Solution
medicine dropper through a one-hole stopper
and sealed the flaskwith it. After that, the student
measured the mass of the setup with a balance.
Finally, the student squeezed the medicine
dropper so the sodium chloride solution mixed
with the silver nitrate in the sealed flask on the
balance. A white precipitate formed.

1. What evidence is there that the reaction described above is a chemical change?

2. Did the mass of the contents of the flask change during this experiment? Support your answer.

3. Write the formulas for the reactants. Write the appropriate symbols to show the phase or state [ (s) = solid;
(I) = liquid; (g) — gas; and (aq) - solution].

-41-
 : Form WS5.5.1A Conservation During Chemical Reactions

CHEMICAL FORMULAS AND EQUATIONS

4. When the electrodes of the apparatus shown to the right are placed in solutions
Electrodes
of silver nitrate, the light bulb lights. What does this show about the solution.

What is the explanation for this? Ughl bulb

5. When ionic compounds such as silver nitrate and sodium chloride dissolve, the
ions separate: AB(*«) -»
a. What ions will be present in solution when silver nitrate and sodium
A+ (a*)+ B- (aq)

chloride dissolve? ___

b. What new combinations of ions could form? (HINT: Opposites attract!)

6. Based on Table F (Solubility Guidelines], which of the products is the white precipitate?

7. Write an equation for the reaction between silver nitrate solution and sodium chloride solution.

The formula mass for silver nitrate (AgNO3) is found as Atomic „ , . , n j ^

shown in the table to the right. Find the formula masses of Element ,, subscript Product
JV13SS
ail the reactants and products of this reaction.
108 x i = 108
REACTANTS Ag
N 14 x i = 14
a. Silver nitrate 170
0 16 x 3 = 48
b. Sodium chloride TOTAL 1 70
PRODUCTS
c.
d.
9. How does the total mass of the reactants compare to the total mass of the products?

Evan P. Silberstein, 2002

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 : Form WS5 . 2 . 1A Name

CHEMICAL FORMULAS AND EQUATIONS Date Period

e Vs.
When a piece of paper is ripped in half, it is still paper -
only smaller! Since no new substances are formed, the /YOLl've
change is only a physical change. When a piece of paper changed
bums, heat is released, there may be some ash left behind,
and two gases, carbon dioxide and water vapor, are released.
since the
These are not only physical changes. They are chemical : fire!
changes as well. Carbon dioxide and water are new
substances. They were not present before the change.
When new substances form, typically, there are a number
of other changes that serve as evidence of the chemical
change. They are: [1] energy changes, such as the heat
released when paper burns; [2] the release of gases, such as
carbon dioxide and water vapor; [3] the formation of a solid
in solution (not in this reaction) or the formation of water;
[4] a change in color—carbon dioxide and water are invisible,
colorless gases while paper is opaque; and [5] a change in
odor - the obvious smell of burning paper comes from the incompletely burned carbon which is left behind to form
the ash. These five changes serve only as evidence of a chemical change. There is no rule that identifies chemical
changes unequivocally except that new substances are formed. That takes a knowledge of chemistry.

Based on the reading above and your knowledge of chemistry state whether each of the following represents
a PHYSICAL CHANGE only, or a CHEMICAL CHANGE as well.

1. Breaking glass _^_^__

2. Dissolving sugar [CUR220}]& + H20(4) -+ C12H22O31(^) + H20(Q]

3. Rusting iron [4Fe(» + 302(g) -+ 2Fe203(g)]

4. Boiling water [H20(C) -* H20fe)] ___^__

5. Digesting sugar [CI2H220U(^) + H2O(4) -> 2C6H1206(a?)] _____

6. Burning gasoline [2C8H18Cg) + 25O2Cg) -* 16CO2(g) +18 H2Ofg)] . _____

7. Respiration [C6H1206(a?) + 602<£) + 6H20(g) -> 6C02(£) + 12H2Ofe)] - . _^_____^___

8. Forming ozone from oxygen [302(g) "t 203(g)]

9. Dissolving salt [NaCK» + H2O(5) ->NaCl(^) + H2O(Q]

10. Exploding dynamite

© Evan P. Silberstein, 2002

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 Chemistry Lab # Name

How many moles?

Purpose; Each chemical has a unique set of properties. One tool to help determine what
a compound is, is its' Gram Formula Mass, or Molar Mass. You will, in this lab, use
your knowledge of chemistry to determine how many moles of a substance is in a given
-—sample: —— • , -.

Problem: _^ ^^_

Hypothesis:

Vocabulary:

1. Mole-

2. Mass -

3. Gram -

4. Molecular Formula -

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Chemistry Lab # Name

5. Gram Formula Mass-

Procedure:

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Chemistry Lab # Name

Observations:

Part 1: Moles of sucrose in a teaspoon of sugar

Mass of sucrose

Molecular Formula for sucrose is C^H^On

Convert mass to moles. Show all work. Use significant figures.

Part 2: Moles of water is one sip

Mass of cup with water ^_______

Mass of cup and water after drinking

Mass of water swallowed

Molecular formula for water

Convert mass to moles. Show all work. Use significant figures.

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Chemistry Lab # Name

Part 3: What's in a name? Calculate the number of moles of chalk needed to write vour
full name. The chemical name for chalk is Calcium Carbonate.

Mass a chalk before writing

Mass of chalk after writing

Mass of chalk used

Chemical"formula for chalk is CaCOs

Convert mass to moles. Show all work. Use significant figures.

Questions:
All questions are to be completed using significant figures and don't forget units.

1. How many moles does 80.0 grams of H20 represent?

2. How many moles does 22.0 grams of C02 represent?

!. What is the mass of 5.0 moles of Ba(CN) 2?

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Chemistry Lab # Name

4. What is the mass of 0.75 moles of CuSO4?

5. Calculate the mass of

a) 2.00 moles of water,

b) 4.38 moles of chlorine,

c) 0.025 moles of ammoni

d) 1 .8 moles of oxygen,

6. Calculate the number of moles in

a) 25 g of helium, He

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Chemistry Lab # Name

b) 12.5 g of methane, CH4

c) 0.364 g of iodine,

d) 40.0 g of sodium, Na

Conclusion:

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 * ' ' * f+ , " .' t ' » B Tt

l-l * ^ 4 "* M ^ - i*

Suga.rjn Bubble
t , »/, "' V-, 4rt , t ' '~"

Purpose
To determine the -
percentage of sugar Note: Chewed gum cannot be placed directly on the balance pan; it must
in bubble gum. be wrapped in paper and the mass of the paper subtracted out. Most
balances are not sensitive enough to measure the mass of one wrapper so
all mass measurements will be of your entire group's wrappers and gum.
Materials
balance, bubble gum 1. Your teacher will give you one piece of bubble gum. Place the
wrapped pieces of gum of everyone hi your group on the balance.
Record the combined mass of all the wrappers and all the
unchewed gum.
2. Unwrap your piece of gum put the gum in your mouth.
Do not throw the wrapper away!
3. Place everyone's empty gum wrappers on the balance. Record the
combined mass of all the wrappers. Do not throw the wrapper away!
4. Chew your gum for 15 minutes.
5. After 15 minutes, put your wrapper up to your mouth and
gently spit your gum into the wrapper. Try not to get too much
saliva on the gum. I
6. Place the wrapped, chewed gum of everyone in your group on
the balance. Record the combined mass.
7. Throw away the gum and wrappers.

J
Mass (g)

Wrappers and unchewed gurn

Wrappers only

Unchewed gum only

Wrappers and chewed gum

Chewed gum

Number of people in group:

Brand of gum:

C.1.13, C.1.16, C.1.22/Curriculum Framework / How Do You Calculate Percent Composition, Amount of Product, and Electron Transfer In One Lab?
Indiana Chemistry Standards Resource, November 2003

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Percentage of Sugar in Bubble Gum (continued)

Analysf^'and.GQnclusioris " L ,:
1. Subtract the mass of the wrappers from the mass of the unchewed gum and wrappers.
Record the mass of the unchewed gum in the data table.

2. Subtract the mass of the wrappers from the mass of the chewed gum and wrappers.
Record the mass of the chewed gum hi the data table.

3. What is the total mass of sugar dissolved by chewing?

4. What is the average mass of sugar dissolved by chewing in each piece of gum?

5. What is the percentage of sugar in a piece of gum?

6. Would your dentist recommend chewing this gum? Why or why not?

7. What assumption is made about the change in mass of the gum before and after chewing?
Explain whether you think this is a valid assumption.

8. How would the results be affected if there was a lot of saliva on the chewed pieces of gum?

C.I.13, C1.16, C.1.22/Curriculum Framework/ How Do You Calculate Percent Composition, Amount of Product, and Electron Transfer In One Lab?
Indiana Chemistry Standards Resource, November 2003

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Name'__ Date. Class

" \. Usethis starting mass of bak

Predicting When baking soda is an ingredient in your recipe, its purpose is to make the
batter rise and produce a product with a light and fluffy texture. That's because baking
soda, or sodium hydrogen carbonate (NaHCO3), decomposes upon heating to form
carbon dioxide gas.
2NaHCO- Na2CO3 CO H2O
Predict how much sodium carbonate (Na2CO3) is produced when baking soda
decomposes.

Materials ring stand, ring, clay triangle, crucible, crucible tongs, Bunsen burner,
balance, 3.0 g baking soda (NaHCO3)

Procedure
1. Measure the mass of a clean, dry crucible. Add about 3.0 g of MaHCO3 and measure
the combined mass of the crucible and NaHCO3. Record both masses and calculate the
mass of the NaHCCX.

the mass of Na2CO3 that will be produced.

3. Set up a ring stand with a ring and clay triangle for heating the crucible.
4. Heat the crucible slowly at first and then with a stronger flame for 7-8 min. Use tongs
to remove the hot crucible. Record your observations during the heating.
5. Allow the crucible to coo! and then obtain the mass of the crucible and sodium
carbonate:

Analysis
1, What were your observations during the heating of the baking soda?

2. How did your calculated mass of sodium carbonate compare with the actual mass you
obtained from the experiment? If the two masses are different, suggest reasons for
the difference.

ChemLab and MiniLab Worksheets Chemistry: Matter and Change • Chapter 12 45

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Name Date Class

ron reacts with copper(ll) sulfate in a single replacement reaction.

f By measuring the mass of iron that reacts and the mass of copper
metal produced, you can calculate the ratio of moles of reactant to
moles of product. This mole ratio can be compared to the ratio found
in the balanced chemical equation.

Problem Objectives MateriaEs

Which reactant is the limit- • Observe a single replace- iron metal filings, 400-mL beaker
ing reactant? How does the ment reaction. 20 mesh 100-mL graduated
experimental mole ratio of • Measure the masses of copper(ll) sulfate cylinder
Fe to Cu compare with the iron and copper. pentahydrate weighing paper
mole ratio in the balanced • Calculate the moles.of balance
chemical equation? What is each metal and the rnole distilled water hot plate
the percent yield? ratio. stirring rod beaker tongs
150-mL beaker

Safety Precautions
Always wear safety glasses and a lab apron.
Hot objects will not appear to be hot,
Do not heat broken, chipped, or cracked glassware.
Turn off the hot plate when not in use.

Pre-Lab Procedure
1. Read the entire CHEMLAB. 1. Measure and record the mass of a clean, dry
2. Prepare all written materials that you will take 150-mL beaker.
into the laboratory. Be sure to include safety 2. Place approximately 12 g of copper(II) sulfate
precautions and procedure notes. Use the data pentahydrate into the 150-mL beaker and meas-
table on the next page. ure and record the combined mass.
3. Is it important that you know you are using the hy- 3. Add 50 mL of distilled water to the copper(H)
drated form of copper(H) sulfate? Would it be poss- sulfate pentahydrate and heat the mixture on the '
ible to use the anhydrous form? Why or why not? hot plate at a medium setting. Stir until all of the
solid is dissolved, but do not boil. Using tongs,
remove the beaker from the hot plate.
4. Measure approximately 2 g of iron metal filings
onto a piece of weighing paper. Measure and
• record the'exact-mass of the firings.
5. While stirring, slowly add the iron filings to the
hot copper(H) sulfate solution.
6. Allow the reaction mixture to stand, without stir-
ring, for 5 minutes to ensure complete reaction.
The solid copper metal will settle to the bottom
of the beaker.

46 Chemistry: Matter and Change • Chapter 12 ChemLab.and MiniLab Worksheets

-55-
 Name Date Class

7. Use the stirring rod to decant (pour off) the liq- Cleanup and Disposal
uid into a 400-mL beaker. Be careful to decant
only the liquid. 1. Make sure the.hot plate is off.
8. Add 15 mL of distilled water to the copper 2. The dry copper can be placed in a waste con-
solid and carefully swirl the beaker to wash the tainer. Wet any residue that sticks to the beaker
copper. Decant the liquid into the 400-mL and wipe it out using a paper towel. Pour the
beaker. unreacted copper(H) sulfate and iron(II) sulfate
9. Repeat step 8 two more times. solutions into a large beaker in the fume hood.
10. Place the 150-mL beaker containing the wet 3. Return all lab equipment to its proper place.
copper on the hot plate. Use low heat to dry the 4. Wash your hands thoroughly after all lab work
copper. and cleanup is complete.
11. Remove the beaker'from the hot plate and allow
it to cool.
12. Measure and record the mass of the cooled
150-mL beaker and the copper.

Mass of empty 150-mL beaker

Mass of 150-rnL beaker + CuSO4-5H2O

Mass of CuSO4-5H20

Mass of iron filings

Mass of 150-rnL beaker and dried copper

Mass, of dried copper

Observations

Analyze and Conclude

1. Observing and Inferring What evidence did you observe that confirms that a chemi-
cal reaction occurred?

2, Applying Concepts Write a balanced chemical equation for the single-replacement

reaction that occurred.

| 3, Interpreting Data From your data, determine the mass of copper produced.

4. Using Numbers Use the mass of copper to calculate the moles of copper produced.

ChemLab and MiniLab Worksheets Chemistry: Matter and Change • Chapter 12 47

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Name Date. _ Class

5, Using Numbers Calculate the moles of iron used in the reaction.

6. Using Numbers Determine the whole number ratio of moles of iron to moles of
copper.

7. Comparing and Contrasting Compare the ratio of moles of iron to moles of copper
from the balanced chemical equation to the mole ratio calculated using your data.

8. Evaluating Results Use the balanced chemical equation to calculate the mass of cop-
per that should have been produced from the sample of iron you used. Use this number
and the mass of copper yon actually obtained to calculate the percent yield.

9, | ^yffljjy *f?M i!M H What was the source of any deviation from the mole ratio calculated
from the chemical equation? How could you improve your results?

i
10. Drawing a Conclusion "Which reactant is the limiting reactant? Explain.

Real-World Chemistry _
1. A furnace that provides heat by brirning methane gas (CH4) must have the correct mix-
ture- of air and fuel to operate efficiently. "What is the mole ratio of air to methane gas. in
the combustion of methane? Hint: Air is 20% oxygen.

2, 'Automobile air bags inflate on impact because a series of gas-producing chemical'reactions

are triggered. To be effective in saving lives, the bags must not overinfLate or underirrflate.
"What factors must automotive engineers take into account hi the design of air bags?

Chemistry: Matter arid-Change • Chapter 12. ChemLab and MiniLab Worksheets

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