WEEK ONE

TOPIC: REVISION/ACIDS

CONTENT

 Definition.
 Properties.

 Preparation and uses.

 pH.

ACIDS

Definition: An acid is substance which in aqueous solution produces hydroxonium ion (H3O+) or
hydrogen ion (H+) as the only positive ion. Also, acids can be referred to as proton donor.

CLASSES OF ACIDS

There are two classes of acids:

(1). Organic acids occur as natural products in plants and animal material.

Organic acids Source

Ethanoic acids Vinegar
Lactic acids Milk
Citric acids Lime, Lemon
Amino acids Proteins
Fatty acids Fats and oils
Ascorbic acids (Vitamin C). Oranges

(2). Inorganic acid: Inorganic acid can be prepared from mineral elements or inorganic matter.

Inorganic acid Formula Constituents

Hydrochloric acid HCl Hydrogen, Chlorine
Tetraoxosulphate(VI) acid H2SO4 Hydrogen, Sulphur & Oxygen
Trioxonitrate(VI) acid HNO3 Hydrogen, Nitrogen & Oxygen

An acid is also defined as a substance which produces hydroxonium ion as the only positive ion when
dissolved in water.

H+(aq) + H2O(l) H3O+(aq)

Acid can be dilute or concentrated depending on the amount of water added. A dilute acid is acid
produced when a large amount of water is added to a small amount of acid. A concentrated acid is acid
produced when only a little amount of water is added to a relatively large amount of acid.

STRENGTH OF AN ACID

The strength of an acid can either be weak or strong.

(1) Strong acids: are acids which ionize completely in aqueous solution and such acid solution having a
high concentration of H+. Examples are HCl, H2SO4 and HNO3.

H2SO4 2H+ + SO42-

HNO3 H+ + NO3-

HCl H+ + Cl-

(2) Weak acids: are acids which ionize or dissociate slightly or partially in
aqueous solution and such acid solution have a low concentration of hydrogen ions. Examples are
ethanoic acid (CH3COOH), H2CO3, H3PO4, H2SO3.

H2CO3 2H+ + CO32-

H3PO4 3H+ + PO43-

CH3COOH H+ + CH3COO-

H2SO3 2H+ + SO32-

BASICITY OF AN ACID

The basicity of an acid is the number of replaceable hydrogen ions, H+, in one molecule of the acid.

Acid Basicity
Hydrochloric acid Monobasic
Tetraoxosulphate (vi) acid Dibasic
Tetraoxophosphate(v) acid Tribasic
Ethanoic acid Monobasic

EVALUATION

1. Define the term acid

 2. Differentiate between strong acid and concentrated acid

3. What is the basicity of the following acids: HCl, HNO3, H2SO4

PHYSICAL PROPERTIES OF ACID

1. They have a sour taste.

2. They turn blue litmus paper to red.

3. They are corrosive in nature especially the strong acid.

4. In aqueous solution, they conduct electricity.

CHEMICAL PROPERTIES OF ACID

1. Reaction with metals: They react with metals to liberate hydrogen gas and salt of metal i.e

Acid + Metal  Salt + Hydrogen gas.

e.g. 2HCl(aq) + Zn(s) ZnCl2(aq) + H2(g)

H2SO4(aq) + Mg(s) MgSO4(aq) + H2(g)

2. They react with soluble bases to form salt and water only. This reaction is known as
neutralization.

Acid + Base  Salt + Water

E.g H2SO4(aq) + 2KOH(aq) K2SO4(aq) + 2H2O(l)

2HCl(aq) + CaO(s) CaCl2(aq) + H2O(l)

3. They react with trioxocarbonates (iv) salts to liberate carbon (iv) oxide, salt and water i.e. Acid
+ trioxocarbonate (iv)  Salt + Water + CO2

E.g 2HCl (aq) + Na2CO3(aq)  2NaCl(aq) + H2O(l) + CO2(g)

PREPARATION OF ACIDS

Acid can be prepared by using the following methods:

 1. Dissolving an acid anhydride in water: Acid anhydride is oxides of non-metal that dissolve in
water to produce the corresponding acids e.g SO2, CO2, CO, NO2, SO3.

SO2(g) + H2O(l) H2SO3(aq)

CO2(g) + H2O(l) H2CO3(aq)

SO3(g) + H2O(l) H2SO4(aq)

2. Combination of constituent elements.

(a).Burning hydrogen in chlorine, in the presence of activated charcoal as the catalyst, yields HCl gas
which dissolves readily in water to give HCl acid.

H2(g) + Cl2(g)  activated charcoal + 2HCl(g)

(b)Heating hydrogen gas and bromine vapour, in the presence of platinum as the catalyst, produces
hydrogen bromide which dissolves readily in water to form hydrobromic acid.

H2(g) + Br2(g)  Platinum + 2HBr(g)

(3)By displacement of a weak or more volatile acid from it salt by a stronger or less

volatile acid. For example

(a)Displacement of the more volatile hydrogen chloride from metallic chloride by the less volatile
concentrated tetraoxosulphate (vi) acid.

NaCl(s) + H2SO4(aq) NaHSO4(aq) + HCl(aq)

(b)Displacement of weaker trioxoborate (iii) acid from ‘borax’ by tetraoxosulphate (vi) acid.

Na2B4O7(s) + H2SO4(aq) + 5H2O(l)  Na2SO4(aq) + 4H3BO3(aq)

Borax Trioxoborate (iii) acid

(4)By precipitating an insoluble sulphide from a metallic salt by hydrogen sulphide

Pb (CH3COO)2(aq) + H2S(g) PbS(s) + CH3COOH(aq)

Uses of acid

(1) Acids are useful chemicals which are used in many industries to make other consumer chemicals
such as fertilizers, detergent and drugs.
(2) They are used in industrial process as drying agents, oxidizing agents and catalysts.

USES OF ORGANIC AND INORGANIC ACID

Name Uses
Needed by industries to make chemicals used to remove rust.
HCl
Used to clean the surface of metals before electroplating.
Needed by industries to make chemicals used as a drying and
dehydrating agent.
H2SO4
Used as an electrolyte in lead-acid accumulators

Required in oil refineries.

HNO3 Needed by industries for making fertilizers, explosives etc.
Boric acid Used as mild antiseptic or germicide.
Tartaric acid Used in making baking soda, soft drinks and health salts
Used in preserving food.
Acetic acid (ethanoic acid)
Used in dyeing silk and other textiles.
Citric acid Used in making fruits juice.
Used in the manufacture of soap. This process is known as
Fatty acid (palmitic and stearic saponification.
acid)
Fatty acid + Caustic soda Soap + H2O.

EVALUATION

1. Mention three physical properties of acids

2. Using balanced equations, state the chemical properties of acids

3. State two methods of preparing acids

4. Outline the uses of acids

pH SCALE

All acidic solution contains H+ and all alkaline solution contains OH- ions. The PH scale measure the
concentration of H+ ions present in a solution and start from 0 to 14

DEFINITION OF pH

This is the measure of the degree of acidity and alkalinity of a solution.

pH is defined as the negative logarithms of the hydrogen ion [H+] concentration to the base of 10.

i.e. pH = -log [H+].

Thus: If [H+] = 0.00001 or 10-5.

log [H+] = log10-5 = -5

pH= -log [H+] = - (-5) = 5.

If [H+] =10-x

Therefore, pH= -log10-x = - (-x) = x

If [H+] = 10-2, PH = 2

DEFINITION OF pOH

POH is defined as the negative logarithms of the hydroxide ion [OH-] concentration to the base of 10.

i.e. pOH= -log [OH-].

PH is the degree of acidity. A solution with PH 7 is neutral. A solution with PH less than 7, i.e. PH 6,5,4,
e.t.c, indicate acidity increasing as the numbers decreases. A solution with PH greater than 7, i.e. PH
8,9,10, e.t.c, indicate alkalinity increasing as the numbers increase.

PH: 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Increasing acidity Neutral Increasing alkalinity

A solution with PH 1 is very acidic [with high concentration of H+]. A solution with pH 13 is very alkaline
[with low concentration of H+, but high concentration of OH-].

Note that: If pH is 1, it has concentration of H+ 10 times greater than pH 2 and 100 times greater than PH
3 e.t.c.

pH 1 > pH 2 > pH 3.

Concentration of H+ 10-1 10-2 10-3.

0.1 0.01 0.001.

Relationship between pH and pOH.

H2O  H+ + OH-
From conductivity measurement, [H+] = 10-7moldm-3, [OH-]=10-7moldm-3.

[H+] [OH-] = Kw=10-7 x 10-7=10-14mol2dm-6.

Taking logarithm of both sides

log ([H+] [OH-]) = logKw

log [H+] + log[OH-] =logKw

Subtracting both sides

-(log[H+] + [OH-]) = -logKw

-log [H+] – log[OH-] = -logKw

-log [H+] + (-log [OH-]) = -logKw

pH + pOH = PKw

pKw = -log10-14 = -(-14) = 14

Therefore, pH + pOH = 14.

Worked examples

1. Find the hydrogen and hydroxide ion concentrations in

(a) 0.01moldm-3 tetraoxosulphate (vi) acid solution.

(b) 0.001moldm-3 potassium hydroxide solution.

Solution

(a). H2SO4(aq)  2H+(aq) + SO42-(aq)

From the equation, 1 moldm-3 H2SO4 ionizes to give 2moldm-3 H+

Therefore, 0.01moldm-3 H2SO4 would ionize to give (2x0.01) moldm-3 H+

[H+] = 2x10-2moldm-3

[H+] [OH-] = 10-14

(2x10-2) [OH-] = 10-14

[OH-] = 10-14

2x 10-2

[OH-] = 0.5x (10-14- -2)

[OH-] =0.5 x10-14+2

[OH-] =0.5x10-12moldm-3.

(b). KOH(aq)  K+(aq) + OH-(aq)

From the equation,

1moldm-3 of KOH ionizes to give 1moldm-3 of OH-

10-3moldm-3 of KOH would ionize to give 10-3moldm-3 of OH-

[OH-]=10-3moldm-3.

[H+] [OH-]=10-14

[H+] (10-3) = 10-14.

[H+] = 10-14

10-3

[H+] = 10-14+3

[H+] = 10-11moldm-3

2. A glass cup of orange juice is found to have a POH of 11.40. Calculate the concentration of the
hydrogen ions in the juice.

Solution

pH + pOH = 14.

pH = 14 – 11.4.

pH = 2.6.

pH = -log [H+]

2.6 =-log [H+].

[H+] = Antilog (-2.6)

[H+] = 0.0025moldm-3

[H+] = 2.5x10-3moldm-3.

Measuring pH of a solution.

We use pH meter and a universal indicator to detect PH of a solution.

Universal indicator is a mixture of indicator and can change to several colours corresponding to a
particular PH and compared with the standard colour provided by the manufacturer of the universal
indicator. Universal indicator measures PH between 3 and 11.

Process:-

Put 10cm3 of test solution in a test tube, add 2 drops of universal indicator and compare with the colour
chart or place 2 drops of test solution on universal indicator paper and compare the colour with the chart.

EVALUATION

1. Define the term pH.

2. What is the pH of a solution having hydrogen ion concentration of 6x 10-9

mol/dm3

GENERAL EVALUATION/REVISION

1. Give the chemical formula of the following acids (a) Tetraoxosulphate (vi) acid

(b) Trioxonitrate (v) acid (c) Oxochlorate (i) acid

2. What is the IUPAC nomenclature of the following (a) HNO2 (b) HOBr (c) H3PO4 (d) H2S
3. Determine the oxidation number of Cl and C in each of the following (a) KClO3

(b) HOCl (c) H2CO3 (d) CO2

4. Mention the laboratory apparatus that are used in for an acid-base titration

What can be used to determine the acidity or alkalinity of a solution?

READING ASSIGNMENT
New School Chemistry for Senior Secondary School by O. S. Ababio, pp97-99, 102-107

WEEKEND ASSIGNMENT

1. The following acids are monobasic except (a) HNO2 (b) HBr (c) HOCl (d) H2SO3
2. Which of the following ions is acidic? (a) K+ (b) NO3- (c) S2- (d) H3O+.

3. The number of hydroxonium ions produced by one molecule of an acid in aqueous solution is it
(a) acidity (b) basicity (c) concentration (d) pH.

4. The basicity of ethanoic acid CH3COOH is: (a) 0 (b) 1 (c) 2 (d) 3

5. A solution with pH 7 is (a) Acidic (b) dilute (c) neutral (d) saturated

THEORY

1. 1. What is (i) an acid (ii) basicity of an acid?

2. What is the basicity of tetraoxophosphate (V) acid.

3. The concentrations of H+ in two solutions are (a) 1 x10-4moldm-3and (b) 5 x 10-9moldm-3 . What
is the PH of each solution?

Bases
Bases: These are substance that produces hydroxide ions (OH) as the only positive ion when dissolved
in water. They are mostly oxides or hydroxides of metals.

Alkalis are bases which are soluble in water

Laboratory Alkalis Potassium Hydroxide, KOH Sodium Hydroxide, NaOH Aqueous Ammonia, NH4OH
Calcium Hydroxide, Ca(OH)2

They do not behave as bases in the absence of water.

Alkalis are therefore substances that produce hydroxide ions, OH-(aq) in water.

Physical Properties of Alkalis

1. Alkalis have a slippery and soap feel

 2. Alkalis are hazardous as well

3. Dilute alkalis are irritants

4. Concentrated alkalis are corrosive and burn skin ( caustic (i.e. burning)alkalis)-

5. Alkalis turn common indicator red litmus to blue

Chemical properties of Alkalis

1. Alkalis react with acids. The reaction is called neutralization reaction

2. Alkalis react with ammonium compounds

They react with heated solid ammonium compounds to produce ammonia gas

(NH4)2SO4(s) + Ca(OH)2(aq)  CaSO4(aq) + 2NH3g) +

2H2O(l)

3. Alkalis are precipitating agent. Alkalis react with salt solution to precipitate metallic hydroxides

e.g

BaSO4 (aq), contains Ba2+(aq) ions

2NaOH(aq) + CaCl2(aq)  Ca(OH)2(aq) + 2NaCl(aq) The solid formed is a precipitate

And the reaction is called precipitation reaction

Strong and Weak Alkalis

Strong Alkalis- are base that completely ionizes in water to form OH-(aq) ions. Their reactions are
irreversible. E.g. NaOH, KOH, Ca(OH)2

Ca(OH)(s) Ca2+(aq) + 2OH-(aq)

Weak Alkalis base that partially ionize in water. The remaining molecules remain unchanged as base.
Their reactions are reversible.

E.g. NH3

NH3 (g) + H2(l) ⇌ NH4+(aq) + OH-(aq)

USES OF ALKALIS

1. Alkalis neutralize acids in teeth (toothpaste) and stomach (indigestion)

2. Soap and detergents contain weak alkalis to dissolve grease

3. Floor and oven cleaners contain NaOH (strong alkalis)

4. Ammonia (mild alkalis) is used in liquids to remove dirt and grease from glass

INDICATORS

Indicators are substances that has different colours in acidic and alkaline solutions

Common indicators:

a. Litmus solution from where paper is made

b. Methyl orange

c. Phenolphthalein

IONIC EQUATION

This is an equation involving ions in aqueous solution, showing formation and changes of ions during the
reaction

Rule to develop ionic equations:

1. Only formulae of ions that changed in oxidation number is included

2. Aqueous solutions are written as ions.
3. liquids, solids and gases written in full

Reaction between Metals and Acids.

For example, reaction of sodium with hydrochloric acid

2Na(s) + 2HCl(aq) 2NaCl(aq) + H2(g)

Its ionic equation is written as:
2Na(s) + 2H+(aq) + 2Cl-(aq) 2Na+(aq) + 2Cl-(aq) + H2(g)
Since 2 Cl (aq) ions did not have a change in its oxidation number, they are not involved in chemical
-

reaction .
As ionic equation is used to show changes in reactions, we omit Cl-(aq) ions. So we are left with:

2Na(s) + 2H+(aq)→ 2Na+(aq) + H2(g)

Reaction between Soluble Ionic Compounds and Acids

e.g. Reaction of sodium hydrogentrioxocargbonate (IV) with hydrochloric acid

NaHCO3(aq) + HCl(aq) NaCl(aq) + CO2(g) + H2O (l)

The ionic equation is:
Na+(aq) + H+(aq) + CO32-(aq)+H+(aq)+Cl-(aq) Na+(aq) +
(aq) +CO2(g)+H2O(l)
Since Na+(aq) and Cl-(aq) ions do not change, we omit them, leaving

H+(aq) + Co32-(aq) + H+(aq) CO2(g) + H2O(l)

CO32-(aq) + 2H+(aq) CO2(g) + H2O(l)

Reaction between Insoluble Ionic Compounds and Acids

e.g. Reaction between iron(II) oxide and Tetraoxosulphate (VI) acid

FeO(s) + H2SO4(aq) FeSO4(aq) + H2O(g)

Its ionic equation is : FeO(s) + 2H+(aq) + SO42-(aq)
SO42-(aq)+H2O(g)

Note: FeO is written in full as its solid (although it’s an ionic compound)

Since SO42-(aq) ions do not change, we omit SO42-ions, leaving:

FeO(s) + 2H+(aq) Fe2+(aq) + H2O(g)

E.g. Reaction between calcium carbonate and hydrochloric acid

CaCO3(s) + 2HCl (aq) CaCl2(aq) + CO2(g) + H2O(l)

Its ionic equation is:

CaCO3(s) + 2H+(aq) + 2Cl-(aq) Ca2+(aq) + 2Cl-(aq) + CO2(g)

+H2O(l)

Since 2 Cl-(aq) ions do not change, we omit Cl-ions, leaving:

CaCO3(s) + 2H+(aq) Ca2+(aq) + CO2(g) + H2O(l)

Reactions Producing Precipitate

E.g. Reaction between calcium hydroxide and barium sulphate

Ca(OH)2(aq) + BaSO4(aq) Ba(OH)2(s) + CaSO4(aq)

Its ionic equation is written as:
Ca2+(aq) + 2OH-(aq) + Ba2+(aq) + SO42-(aq)
Ca2+(aq) + SO42-(aq)

Since Ca2+(aq) and SO42-(aq) ions don’t change, we omit them, leaving:

Ba2+(aq) + 2OH-(aq) Ba(OH)2(s)

Displacement Reactions
E.g. Reactions between magnesium with zinc sulphate
Mg(s) + ZnSO4(aq) MgSO4(aq) + Zn(s)
Its ionic equation is written as:
Mg(s) + Zn2+(aq) + SO42 (aq) Mg2+(aq) + SO42-(aq) + Zn(s)

Since SO42-(aq) ions do not change, we omit them, leaving:

Mg(s) + Zn2+(aq) Mg2+(aq) + Zn(s)

EVALUATION: 1. Define

a. acid
b. base

2. Explain strong and weak acids giving two examples of each

3. Explain strong and weak bases giving two examples of each

4. State three physical and chemical properties each of acids and bases

5. Outline three uses each of acids and bases

6. Define Ionic equations. List three examples of ionic equations