Worksheet (Mole Concept 2) Page 1 of 2

NSS F.4 1st Term Mole Concept Homework 2 (Percentage by Mass / Chemical Formula) Short Questions Regular 1.   A metal oxide MO contains 79.9% by mass of metal M. Find the relative

atomic mass of M. 2.   26.88 g of a Group I chloride contains 5.68 g of chlorine. Find the

relative atomic mass of the metal M. 3.   19.85 g of phosphorus combine with 25.61 g of oxygen to form an oxide.

Deduce the empirical formula for this oxide. 4.   5.0 g of sulphur, after combination, give 10.0 g its oxides. Find the

empirical formula of this oxide. 5.   2.48 g of Na2CO3 • nH2O, on heating, left 2.12 g of the anhydrous salt.

Find the value of n. 6.   If the formula of a hydrate is MgSO4 • xH2O and the percentage by mass

of water of crystallization is 51.22, what is the value of x? 7.   A colourless organic liquid L contains 40.00% of carbon, 6.67% of

hydrogen and 53.3% of oxygen. If the molar mass of L is 60.0 g mol–1, calculate the empirical and molecular formula of L.

8.   A 23.2 g sample of an organic compound containing carbon, hydrogen,

and oxygen was burnt in excess oxygen and yielded 52.8 g of carbon dioxide and 21.6 g of water. Determine the empirical formula of the compound.

Challenging 9.   0.166 mole of a hydrated salt, on strong heating, gave 17.94 g of water.

Find the number moles of water of crystallization in one mole of hydrated salt.

10.   A hydrate contain 16.08% sodium, 4.20% carbon, 6.99% hydrogen and

72.73% oxygen by mass. If all the hydrogen atoms of the hydrate are in the form of water of crystallization, determine its empirical formula.

Worksheet (Mole Concept 2) Page 2 of 2

Multiple Choice Regular 1.   [01-26]

What is the percentage by mass of chromium in potassium dichromate? A. 17.7 B. 25.1 C. 35.4 D. 40.8

2.   [95-06]

Which of the following fertilizers contains the largest percentage by mass of nitrogen? A. ammonium chloride B. ammonium sulphate C. potassium nitrate D. sodium nitrate

3.   [02-03]

An oxide of element X has the formula X2O3. 10.2 g of this oxide contains 5.4 g of X. What is the relative atomic mass of X? A. 12.0 B. 18.0 C. 27.0 D. 36.0

4.   [99-17]

The compound X2S contains 58.9 % of X by mass. What is the relative atomic mass of X? A. 11.5 B. 23.0 C. 39.0 D. 46.0

5.   [00-04]

Metal X forms an oxide. 27.53 g of this oxide contains 24.96 g of X. What is the mole ratio of X to oxygen in the oxide? Given that the relative atomic mass of X is 207. A. 1 : 1 B. 1 : 2 C. 2 : 3 D. 3 : 4

6.   [03-11]

A sample of MgSO4 • xH2O of mass 123.2 g contains 63.0 g of water of crystallization. What is the value of x? A. 4 B. 5 C. 6 D. 7

7.   [94-18]

The formula of hydrated magnesium sulphate crystals is MgSO4 • xH2O. When 3.80 g of the hydrated crystals are heated, 2.00 g of anhydrous magnesium sulphate are produced. What is the value of x? A. 3 B. 4 C. 5 D. 6

8.   [98-10]

The formula for hydrated iron(II) sulphate is FeSO4 • xH2O. On strong heating, 20.1 g of the sulphate produces 9.1 g of water. What is the value of x? A. 5 B. 6 C. 7 D. 8