1) The document discusses chemical formulas and their uses in determining percent composition of elements in compounds.
2) Chemical formulas show the ratio of elements in a compound at the molecular level and can be used to calculate percent composition by mass.
3) The empirical formula gives the simplest whole number ratio of elements in a compound and is determined from percent composition data. The molecular formula may contain multiple units of the empirical formula to match the actual molar mass.
1) The document discusses chemical formulas and their uses in determining percent composition of elements in compounds.
2) Chemical formulas show the ratio of elements in a compound at the molecular level and can be used to calculate percent composition by mass.
3) The empirical formula gives the simplest whole number ratio of elements in a compound and is determined from percent composition data. The molecular formula may contain multiple units of the empirical formula to match the actual molar mass.
1) The document discusses chemical formulas and their uses in determining percent composition of elements in compounds.
2) Chemical formulas show the ratio of elements in a compound at the molecular level and can be used to calculate percent composition by mass.
3) The empirical formula gives the simplest whole number ratio of elements in a compound and is determined from percent composition data. The molecular formula may contain multiple units of the empirical formula to match the actual molar mass.
1) The document discusses chemical formulas and their uses in determining percent composition of elements in compounds.
2) Chemical formulas show the ratio of elements in a compound at the molecular level and can be used to calculate percent composition by mass.
3) The empirical formula gives the simplest whole number ratio of elements in a compound and is determined from percent composition data. The molecular formula may contain multiple units of the empirical formula to match the actual molar mass.
CHEMICAL FORMULAS Information from the chemical formula: a. The compound is made up of two elements, namely carbon and oxygen. b. One molecule of CO2 is made up of one atom of carbon and two atoms of oxygen. c. One mole of CO2 molecules will have one mole of C atoms and two moles of O atoms. d. The ratio of the moles of C to the moles of O in CO2 is 1:2. e. CO2 is composed of 27.29% carbon and 72.71% oxygen. The chemical formula provides the percent composition of CO2. PERCENT COMPOSITION BY MASS PERCENT COMPOSITION BY MASS
is the percent by mass of each element in a compound
n = the number of atoms of the element
Therefore, CO2 is composed of 27.29% C atom and 72.71% O atom. 1. Calculate the percent composition of NaCl.
%Na = 1 x 22.99g/mol Na x 100 = 39.34% Na
58.44 g/mol NaCl
% Cl = 1 x 35.45g/mol x 100 = 60.66% Cl
58.44 g/mol NaCl The chemical formula of glucose is C6H12O6. Determine its percent composition. %C = 6 x 12.01g/mol C x 100 = 39.99% C 180.18 g/mol C6H12O6 %H = 12 x 1.01 g/mol H x 100 = 6.727% H 180.18 g/mol C6H12O6 %O = 6 x 16.0g/mol O x 100 = 53.28% O 180.18 g/mol C6H12O6 Which element comprising Mg(OH)2 has the highest percentage by mass? %Mg = 1 x 24.31g/mol Mg x 100 = 41.68% Mg 58.33 g/mol Mg(OH)2 %O = 2 x 16.00 g/mol O x 100 = 54.86% O 58.33 g/mol Mg(OH)2 %H = 2 x 1.01g/mol H x 100 = 3.46% H 58.33 g/mol Mg(OH)2 Therefore, oxygen has the highest percentage by mass. EMPIRICAL FORMULA EMPIRICAL FORMULA
Empirical formula of a compound can be calculated from the percent
composition. Because percentage is given, it is convenient to assume 100.00 grams of the compound. Example. A compound is found to consist of 7.81% C and 92.19% Cl. What is the empirical formula of the compound? Assume 100.00 grams of the compound. The sample will therefore contain 7.81 g C and 92.19 g Cl. The grams are converted to moles to get the ratios of the moles of the elements in the compound: The compound is C0.650Cl2.601. But chemical formulas are expressed in whole numbers. Empirical formulas are expressed as the lowest whole number ratio between the atoms. To convert to whole numbers, divide the number of moles by the smallest value (that is 0.650).
The empirical formula is C1Cl4 or CCl4.
Example. A compound is found to consist of 43.64% P and 56.36% O. The molar mass for the compound is 283.88 g/mol. What is the empirical formula and molecular formula of the compound? Assume 100.00 grams of the compound. What is the mass of each element in 100.00 grams of compound? P = 43.64g 0 = 56.36g Divide the mole values by the smallest value to get
The compound is PO2.5.
But the subscripts are still not whole numbers. Multiply the subscripts by a factor to get the smallest whole number. When multiplied by 2, the empirical formula is P2O5. MOLECULAR FORMULA Formula which describes the composition of compounds. It gives the information of how many atoms are in each molecule. Example: Compare the mass of the empirical formula to the molar mass; Mass of the Empirical Formula P2O5 = 141.94 g/mol Molar Mass of P2O5 = 283.88 g/mol n=2 is the whole number multiple
Therefore, the molecular formula is (P2O5)2 or P4O10.
Example:
Naphthalene has a molecular formula of C8H10.
One molecule of naphthalene is made up of two elements, Carbon and Hydrogen. Molecular mass of naphthalene is 106.16 amu.