Question 1

Which statement best describes the Law of Constant Composition?

Accepted Answer

All samples of a given compound have the same proportions of their constituent elements by mass.

Question 2

A sample of pure water is found to contain 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$\frac{16.0\ \mathrm{g}\ O}{2.0\ \mathrm{g}\ H} = 8.0:1$$

Question 3

Which of the following best explains why sodium chloride (NaCl) has very different properties from its constituent elements, sodium and chlorine?

Accepted Answer

When sodium and chlorine chemically combine, they form a compound with new properties distinct from the original elements.

Question 4

Which of the following is a correct chemical formula for a compound containing magnesium ions and nitrate ions?

Accepted Answer

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

Question 5

If a compound is composed of 14.0 g of nitrogen and 3.0 g of hydrogen, what is the mass ratio of nitrogen to hydrogen?

Accepted Answer

$$\frac{14.0\ \mathrm{g}\ N}{3.0\ \mathrm{g}\ H} = 4.7:1$$

Question 6

Which of the following is the correct formula for a compound formed between potassium ions and oxide ions?

Accepted Answer

$$\mathrm{K_2O}$$

Question 7

What is the empirical formula for a compound with the molecular formula $$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$?

Accepted Answer

$$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$

Question 8

Which of the following best describes a polyatomic ion?

Accepted Answer

A group of atoms that act as a single unit with a net charge.

Question 9

Which of the following is the correct formula for aluminum sulfate, given that the sulfate ion is $$\mathrm{SO_4$^{2-}}$$ and the aluminum ion is $$\mathrm{Al$$^{3+}$$}$$?

Accepted Answer

$$\mathrm{Al_2$(SO_4$)_3}$$

Question 10

Which of the following statements is true regarding the order of elements in a chemical formula for a compound containing only nonmetals?

Accepted Answer

The more metal-like element (usually to the left on the periodic table) is listed first.

Question 11

Which of the following is the correct formula for a compound formed between calcium ions and phosphate ions ($$\mathrm{PO_4$^{3-}}$$)?

Accepted Answer

$$\mathrm{Ca_3$(PO_4$)_2}$$

Question 12

Which of the following best distinguishes a molecular compound from an ionic compound?

Accepted Answer

A molecular compound is composed of only nonmetals, while an ionic compound is composed of metals and nonmetals.

Question 13

A student is asked to write the formula for a compound containing lithium ions and bromide ions. Which is correct?

Accepted Answer

$$\mathrm{LiBr}$$

Question 14

Which of the following is the correct formula for iron(III) nitrate?

Accepted Answer

$$\mathrm{Fe(NO_3$)_3}$$

Question 15

Which of the following best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

The empirical formula gives the simplest whole-number ratio of atoms, while the molecular formula gives the actual number of atoms of each element in a molecule.

Question 16

Which of the following is the correct formula for a compound formed between aluminum ions and carbonate ions ($$\mathrm{CO_3$^{2-}}$$)?

Accepted Answer

$$\mathrm{Al_2$(CO_3$)_3}$$

Question 17

A compound is found to contain only magnesium and nitrogen. What is the correct formula for this compound?

Accepted Answer

$$\mathrm{Mg_3N_2}$$

Question 18

Which of the following is the correct formula for sodium hydroxide?

Accepted Answer

$$\mathrm{NaOH}$$

Question 19

Which of the following best explains why changing the subscript in a chemical formula changes the compound?

Accepted Answer

The subscript defines the number of atoms of each element; changing it alters the identity and properties of the compound.

Chemical Compounds, Formulas, and the Law of Constant Composition

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