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Chemical Formulas Practice Test Questions

Chemistry Test Questions

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This collection of ten multiple choice questions deals with the basic concepts of chemical formulas. Topics include simplest and molecular formulas, mass percent composition and naming compounds.

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 1

The 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 2

A 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**

A. C3H6O3
B. C4H26O
C. C4H10O2
D. C5H14O

Question 3

A 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:

A. PO2
B. P0.4O
C. P5O2
D. P2O5

Question 4

Which 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 5

A 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 6

How 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 7

The ionic compound containing Fe3+ and SO42- would have the formula:

A. FeSO4
B. Fe2SO4
C. Fe2(SO4)3
D. Fe3(SO4)2

Question 8

A 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 9

The compound with molecular formula N2O3 would be called:

A. nitrous oxide
B. dinitrogen trioxide
C. nitrogen(III) oxide
D. ammonia oxide

Question 10

Copper 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
C. CuSO4
D. CuSO4 + 5 H2O

Answers to Questions

1. 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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