Q: Which of the following best describes Avogadro’s number and its significance in chemistry?

It is the number of particles in one mole, $$6.022 \times 10$$^{23}$$.

Q: A chemist has 23.0 g of mercury (Hg). How many moles of Hg does this represent? (Molar mass of Hg = 200.6 g/mol)

$$1.15 \times 10$$^{-1}$$ mol Hg

Q: How many titanium (Ti) atoms are contained in 7.80 g of Ti? (Molar mass of Ti = 47.87 g/mol)

$$2.25 \times 10$$^{26}$$ atoms Ti

Q: What is the mass of $$1.28 \times 10$$^{8}$$ atoms of neon (Ne)? (Molar mass of Ne = 20.18 g/mol)

$$4.29 \times 10$$^{-15}$$ g Ne

Q: How many hydrogen atoms are present in 7.53 g of $$\mathrm{H_2S}$$? (Molar mass $$\mathrm{H_2S} = 34.08 g/$$mol)

$$2.66 \times 10$$^{23}$$ atoms H

Q: How many sulfur atoms are in 1.00 mol of $$\mathrm{S_8$}$$ molecules?

$$4.82 \times 10$$^{24}$$ atoms S

Question 1

Which of the following best describes Avogadro’s number and its significance in chemistry?

Accepted Answer

It is the number of particles in one mole, $$6.022 	imes 10$$^{23}$$.

Question 2

A chemist has 23.0 g of mercury (Hg). How many moles of Hg does this represent? (Molar mass of Hg = 200.6 g/mol)

Accepted Answer

$$1.15 	imes 10$$^{-1}$$ mol Hg

Question 3

How many titanium (Ti) atoms are contained in 7.80 g of Ti? (Molar mass of Ti = 47.87 g/mol)

Accepted Answer

$$2.25 	imes 10$$^{26}$$ atoms Ti

Question 4

What is the mass of $$1.28 	imes 10$$^{8}$$ atoms of neon (Ne)? (Molar mass of Ne = 20.18 g/mol)

Accepted Answer

$$4.29 	imes 10$$^{-15}$$ g Ne

Question 5

What is the molar mass of aluminum hydroxide, $$\mathrm{Al(OH)_3}$$?

Accepted Answer

78.00 g/mol

Question 6

How many moles of $$\mathrm{$$TiCl_4$$}$$ are there in 12.5 g of titanium(IV) chloride? (Molar mass = 189.68 g/mol)

Accepted Answer

0.0659 mol

Question 7

Calculate the percent composition of oxygen in $$\mathrm{H_2O_2} ($$hydrogen peroxide). (Molar mass H = 1.008 g/mol, O = 16.00 g/mol)

Accepted Answer

94.06 %

Question 8

A sample of zinc reacts with oxygen to form 2.03 g of ZnO. If 1.63 g of Zn was used, what is the percent composition of Zn in ZnO?

Accepted Answer

80.3 %

Question 9

A compound contains 56.68% K, 8.68% C, and 34.73% O by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{K_2CO_3}$$

Question 10

A compound with the empirical formula $$\mathrm{NO_2$}$$ has a molar mass of 92.00 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{N_2O_4}$$

Question 11

How many hydrogen atoms are present in 7.53 g of $$\mathrm{H_2S}$$? (Molar mass $$\mathrm{H_2S} = 34.08 g/$$mol)

Accepted Answer

$$2.66 	imes 10$$^{23}$$ atoms H

Question 12

A compound contains 80.0% C and 20.0% H by mass and has a molar mass of 30.00 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C_2H_6}$$

Question 13

Which of the following statements about empirical and molecular formulas is correct?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms in a compound.

Question 14

If you have 8.21 mol of potassium (K), what is the mass in grams? (Molar mass of K = 39.10 g/mol)

Accepted Answer

321 g

Question 15

How many sulfur atoms are in 1.00 mol of $$\mathrm{S_8$}$$ molecules?

Accepted Answer

$$4.82 	imes 10$$^{24}$$ atoms S

Question 16

A compound contains 2.233 g Fe and 1.926 g S. What is its empirical formula?

Accepted Answer

$$\mathrm{Fe_2S_3}$$

Question 17

Which of the following best explains why the mole is a useful unit in chemistry?

Accepted Answer

It allows chemists to count large numbers of tiny particles by weighing measurable amounts.

Question 18

What is the first step in calculating the percent composition of an element in a compound from its formula?

Accepted Answer

Calculate the molar mass of the compound.

Question 19

A compound with the empirical formula $$\mathrm{CH_2$}$$ has a molar mass of 42.08 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C_3H_6}$$

Quantitative Composition of Compounds: The Mole, Molar Mass, Percent Composition, Empirical and Molecular Formulas

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