It is a good idea to review these topics by reading the following articles:
How to Calculate Mass Percent
Molecular Formula and Empirical Formula
Simplest Formula from Percent Composition Example Problem
Answers to each question appear after the end of the test.
Question 1The simplest formula of a substance shows:
A. the actual number of atoms of each element in one molecule of a substance.
B. the elements that make up one molecule of the substance and the simplest whole number ratio between the atoms.
C. the number of molecules in a sample of the substance.
D. the molecular mass of the substance.
Question 2A compound is found to have a molecular mass of 90 atomic mass units and simplest formula of C2H5O. The molecular formula of the substance is:
**Use atomic masses of C = 12 amu, H = 1 amu, O = 16 amu**
Question 3A substance of phosphorus (P) and oxygen (O) is found to have a mole ratio 0.4 moles of P for every mole of O.
The simplest formula for this substance is:
Question 4Which sample contains the greatest number of molecules?
**Atomic masses are given in parentheses**
A. 1.0 g of CH4 (16 amu)
B. 1.0 g of H2O (18 amu)
C. 1.0 g of HNO3 (63 amu)
D. 1.0 g of N2O4 (92 amu)
Question 5A sample of potassium chromate, KCrO4, contains 40.3% K and 26.8% Cr. The mass percent of O in the sample would be:
A. 4 x 16 = 64
B. 40.3 + 26.8 = 67.1
C. 100 - (40.3 + 26.8) = 23.9
D. The mass of the sample is needed to finish the calculation.
Question 6How many grams of oxygen are in one mole of calcium carbonate, CaCO3?
**Atomic mass of O = 16 amu**
A. 3 grams
B. 16 grams
C. 32 grams
D. 48 grams
Question 7The ionic compound containing Fe3+ and SO42- would have the formula:
Question 8A compound with molecular formula Fe2(SO4)3 would be called:
A. ferrous sulfate
B. iron(II) sulfate
C. iron(III) sulfite
D. iron(III) sulfate
Question 9The compound with molecular formula N2O3 would be called:
A. nitrous oxide
B. dinitrogen trioxide
C. nitrogen(III) oxide
D. ammonia oxide
Question 10Copper sulfate crystals are actually crystals of copper sulfate pentahydrate. The molecular formula for copper sulfate pentahydrate is written as:
A. CuSO4 · 5 H2O
B. CuSO4 + H2O
D. CuSO4 + 5 H2O
Answers to Questions1. B. the elements that make up one molecule of the substance and the simplest whole number ratio between the atoms.
2. C. C4H10O2
3. D. P2O5
4. A. 1.0 g of CH4 (16 amu)
5. C. 100 - (40.3 + 26.8) = 23.9
6. D. 48 grams
7. C. Fe2(SO4)3
8. D. iron(III) sulfate
9. B. dinitrogen trioxide
10. A. CuSO4 · 5 H2O
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