Empirical And Molecular Formulae

Empirical formula is the formula which shows the simplest whole number ratios of atoms present in a compound while molecular formula is the formula which shows the actual number of each kind of atoms present in the molecule. The molecular formula of a compound is a whole number multiple of its empirical formulae.

GENERAL EVALUATION/REVISION

1. An organic compound has the empirical formula CH2. If its molecular mass is 42gmol^-1,      what is the molecular formula?
2. Determine the relative molecular mass of calcium trioxocarbonate (v).
3. Define the term radical.
4. Write the formula of the following compounds

A. Mercury (i) dioxonitrate (iii)

            B.Sodium hydrogen trioxocarbonate (IV)

C. Oxochlorate (I) acid

READING ASSIGNMENT

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New School Chemistry for Senior Secondary School by O. Y. Ababio, Pg 31-32

WEEKEND ASSIGNMENT

1. The % by mass of carbon in CO2 is A.37% B. 27% C. 48% D. 52%
2. What is the molar mass of Na₂SO₄? A. 172 B.168 C.142 D.133
3. The empirical formula of a compound is CH, the molecular formula could be A. C₂H₄

B.CH₄C. C₇H₁₂D. C₆H₆

• An oxide of nitrogen contains 69.6% of oxygen by mass. Its empirical formula is A. N₂O₃      B. N₂O₂C. N₂O D. NO₂
• 5.0g of an oxide of a metal (M) gave 4.0g of the metal when reduced with hydrogen. What is the empirical formula of the oxide? [M=64, O=16] A. MO B. MO₂C. M₂O D. M₂0₃

THEORY

1. Calculate the % by mass of water of crystallization in Al₂(SO₄)₃.9H₂O
2. Two compounds X and Y have the same % composition by mass 92.3% carbon and 7.7% hydrogen. Calculate the:

A. Empirical  formula of X and Y

B. Molecular formula of each compound if the molar mass of X is 26gmol^-1 and Y is 78gmol^-1.

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