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 water contains 16.0 g of oxygen and 2.0 g of hydrogen. What is the oxygen-to-hydrogen mass ratio in water?

Accepted Answer

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

Question 3

Which of the following is NOT a property of elemental sodium?

Accepted Answer

Forms a yellow gas with a pungent odor

Question 4

Why is sodium chloride (NaCl) safe to eat, even though its constituent elements are dangerous?

Accepted Answer

The properties of compounds are different from the properties of the elements that compose them.

Question 5

Which of the following best describes a chemical formula?

Accepted Answer

A representation of the elements present and the relative number of atoms of each in a compound.

Question 6

What is the correct chemical formula for a compound formed from magnesium ions ($$\mathrm{Mg$$^{2+}$$}) $$and chloride ions ($$\mathrm{Cl^-}$$)?

Accepted Answer

$$\mathrm{$$MgCl_2$$}$$

Question 7

Which of the following compounds contains a polyatomic ion?

Accepted Answer

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

Question 8

Given the ions $$\mathrm{Al$$^{3+}$$}$$ and $$\mathrm{SO_4$^{2-}}$$, what is the correct formula for the resulting ionic compound?

Accepted Answer

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

Question 9

Which of the following is a molecular compound?

Accepted Answer

$$\mathrm{CO_2$}$$

Question 10

If a compound contains 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms, what is its chemical formula?

Accepted Answer

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

Question 11

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

Accepted Answer

Subscripts indicate the number of atoms of each element, so changing them alters the identity and properties of the compound.

Question 12

What is the correct formula for a compound formed from potassium ions ($$\mathrm{K^+}) $$and phosphate ions ($$\mathrm{PO_4$^{3-}}$$)?

Accepted Answer

$$\mathrm{K_3PO_4}$$

Question 13

Which of the following is the empirical formula for hydrogen peroxide ($$\mathrm{H_2O_2}$$)?

Accepted Answer

$$\mathrm{HO}$$

Question 14

A compound is formed from aluminum ions ($$\mathrm{Al$$^{3+}$$}) $$and bromide ions ($$\mathrm{Br^-}). $$What is its chemical formula?

Accepted Answer

$$\mathrm{$$AlBr_3$$}$$

Question 15

Which of the following is true about the composition of compounds?

Accepted Answer

Compounds have elements combined in fixed, whole-number ratios.

Question 16

What is the correct formula for a compound formed from calcium ions ($$\mathrm{Ca$$^{2+}$$}) $$and nitrate ions ($$\mathrm{NO_3$^-}$$)?

Accepted Answer

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

Question 17

Which of the following is a correct statement about the order of elements in a chemical formula for a compound containing only nonmetals?

Accepted Answer

The more metal-like element is listed first.

Question 18

What is the correct formula for a compound formed from magnesium ions ($$\mathrm{Mg$$^{2+}$$}) $$and phosphate ions ($$\mathrm{PO_4$^{3-}}$$)?

Accepted Answer

$$\mathrm{Mg_3$(PO_4$)_2}$$

Question 19

Which of the following is the correct formula for a compound formed from aluminum ions ($$\mathrm{Al$$^{3+}$$}) $$and nitrogen ions ($$\mathrm{N$$^{3-}$$}$$)?

Accepted Answer

$$\mathrm{AlN}$$

Question 20

Which of the following best describes an ionic compound?

Accepted Answer

A compound composed of positive and negative ions held together by electrostatic forces.

Chemical Formulas, Compounds, and the Law of Constant Composition

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