Grade
Subject
Topic
: AP
: Chemistry
: Percentage, Molecular & Empirical formula
Percentage, Molecular & Empirical formula
Instructions:- The atomic masses of the elements may be taken from the
periodic table.
(1) The formula, which gives the actual number of atoms of various elements
presents in a molecule, is called as ___
(2)The formula which gives the simplest whole number ratio of atoms of various elements
present in a molecule is called as_____
(3) Molecular formulae of some compounds are given below. What will be their empirical
formula?
(a) N2O4 (b) B2H6 (c) C2H4
(4) The formula of table salt is NaCl. Calculate the percentage composition of each of its
elements.
(5) Which of the following compound has higher percentage of oxygen?
a) C2H4O2 or (b) CH4O
(6) A compound contains only carbon and hydrogen. The percentage composition
of Carbon is 75% and that of hydrogen is 25%. Calculate the empirical formula of
the compound.
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(7) Laughing gas has two elements, nitrogen and oxygen. The percentage
composition of these elements is 63.6% and 36.4% respectively. The molar mass
of the gas is 44. Calculate the molecular formula of laughing gas.
(8) A compound containing carbon, hydrogen and oxygen gave the following data
on analysis. Carbon = 57.82%, H= 3.6% .The molar mass of the compound is 166.
Calculate the molecular formula of the compound.
(9) A compound has an empirical formula of C4H4O and a molar mass of 136 grams per
mole. What is its molecular formula?
(10) Calculate the percentage of oxygen in each of the following compounds
(a) K2Cr2O7 (b) H2O (c) Fe2 (SO4)3
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Answer Key:(1) Molecular formula
(2) Empirical Formula
(3) (a) NO2 (b) BH3 (c) CH2
(4) % of Na in NaCl = 39.31, % of Cl in NaCl = 60.68
(5) C2H4O2 has higher percentage of oxygen
(6) Empirical formula = CH4
(7) Molecular formula = N2O
(8) Molecular formula -C8 H 6 O4
(9) Molecular formula - C8H8O
(10) (a) % Of oxygen in K2Cr2O7 = 38.09%
(b) % of oxygen in H2O = (16/18) x 100 = 88.88%
(c)% of oxygen in Fe2 (SO4)3 = (192/400) x 100 = 48%
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