Question 1

Which statement best describes the Law of Constant Composition?

Accepted Answer

A compound always contains the same elements in the same ratio by mass.

Question 2

Who is credited with formulating the Law of Constant Composition?

Accepted Answer

Joseph Proust

Question 3

Which of the following is a correct empirical formula for a compound containing two phosphorus atoms for every five chlorine atoms?

Accepted Answer

$$\mathrm{P_2Cl_5}$$

Question 4

Which element is listed first in a chemical formula?

Accepted Answer

The more metallic element

Question 5

What is the difference between a molecular formula and an empirical formula?

Accepted Answer

A molecular formula shows the actual number of atoms of each element in a molecule, while an empirical formula shows the simplest whole-number ratio of the elements.

Question 6

Which of the following elements exists as a diatomic molecule under standard conditions?

Accepted Answer

Oxygen

Question 7

Identify the block in the periodic table that contains metals that tend to form more than one type of ion.

Accepted Answer

Transition metals (d-block)

Question 8

Which of the following compounds contains a polyatomic ion?

Accepted Answer

$$\mathrm{Ba(NO_3$)_2}$$

Question 9

Two samples of sodium chloride are decomposed into their constituent elements. One sample produces 4.65 g of sodium and 7.16 g of chlorine, and the other sample produces 2.57 g of sodium and 4.11 g of chlorine. Are these results consistent with the law of constant composition? Explain your answer.

Accepted Answer

Yes, because the ratio of sodium to chlorine by mass is approximately the same in both samples: $$\frac{4.65}{7.16} \approx \frac{2.57}{4.11}.$$

Question 10

Upon decomposition, one sample of magnesium fluoride produced 1.65 g of magnesium and 2.57 g of fluorine. A second sample produced 3.32 g of magnesium and 5.17 g of fluorine. According to the law of constant composition, what is the ratio of the masses of the two elements in both samples?

Accepted Answer

$$\frac{1.65}{2.57} = 0.642$$ and $$\frac{3.32}{5.17} = 0.642$$; the ratio is the same in both samples.

Question 11

Which of the following is the correct formula for the compound containing potassium and chromate?

Accepted Answer

$$\mathrm{K_2CrO_4}$$

Question 12

Classify each element as atomic or molecular: chlorine, argon, cobalt, hydrogen.

Accepted Answer

Chlorine: molecular; Argon: atomic; Cobalt: atomic; Hydrogen: molecular

Question 13

Classify each compound as ionic or molecular: $$\mathrm{CS_2$}$$, $$\mathrm{CuO}$$, $$\mathrm{KI}$$, $$\mathrm{$$PCl_3$$}.$$

Accepted Answer

$$\mathrm{CS_2$}$$: molecular; $$\mathrm{CuO}$$: ionic; $$\mathrm{KI}$$: ionic; $$\mathrm{$$PCl_3$$}$$: molecular

Question 14

Which of the following is the correct formula for the compound formed from potassium and acetate?

Accepted Answer

$$\mathrm{KC_2H_3O_2}$$

Question 15

Name the ionic compound $$\mathrm{$$NaClO_4$$}.$$

Accepted Answer

Sodium perchlorate

Question 16

Write the formula for carbon monoxide.

Accepted Answer

$$\mathrm{CO}$$

Question 17

Which of the following is a molecular compound?

Accepted Answer

$$\mathrm{$$PCl_3$$}$$

Question 18

Which of the following substances is composed of formula units?

Accepted Answer

$$\mathrm{$$CCl_4$$}$$

Question 19

Which of the following is the correct formula for diphosphorus pentasulfide?

Accepted Answer

$$\mathrm{P_2S_5}$$

Fundamental Concepts in Introduction to Chemistry: Law of Constant Composition, Chemical Formulas, and Classification of Compounds

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