$$\frac{1 \text{ mol}}{\text{molar mass (g)}}$$ then $$\frac{6.022 \times 10$$^{23}$$ \text{ particles}}{1 \text{ mol}}$$

$$\frac{1.222}{1.912} \times 100 = 63.93\%$$

$$\text{C}_6\text{H}_{12}\text{O}_2$$

$$\frac{8.323 \times 10$$^{22}$$}{6.022 \times 10$$^{23}$$} = 0.138$$ mol

Question 1

Which of the following samples shown in the first image contains exactly 1 mole of atoms?

Accepted Answer

65.4 g Zn

Question 2

Based on the mole road map (second image), which conversion factor would you use to convert from grams of a substance to number of particles?

Accepted Answer

$$\frac{1 	ext{ mol}}{	ext{molar mass (g)}}$$ then $$\frac{6.022 	imes 10$$^{23}$$ 	ext{ particles}}{1 	ext{ mol}}$$

Question 3

A sample contains 28.1 g of Si (see first image). How many atoms of silicon are present in this sample?

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 4

Which process is depicted in the third image, and what is its primary purpose in chemical analysis?

Accepted Answer

Combustion analysis; to determine the empirical formula of a compound

Question 5

A 1.912 g sample of calcium chloride is found to contain 0.690 g Ca and 1.222 g Cl. What is the mass percent of chlorine in the sample?

Accepted Answer

$$\frac{1.222}{1.912} 	imes 100 = 63.93\%$$

Question 6

If you have 8.25 g of potassium hydrogen sulfate ($$	ext{KHSO}_4$$), how many moles of $$	ext{KHSO}_4$$ are present? (Molar mass = 136.17 g/mol)

Accepted Answer

$$\frac{8.25}{136.17} = 0.0606$$ mol

Question 7

A compound contains 63.52% iron and 36.48% sulfur by mass. What is the empirical formula of this compound?

Accepted Answer

$$	ext{FeS}$$

Question 8

A 0.400 g sample of a white powder contains 0.141 g K, 0.115 g S, and 0.144 g O. What is the empirical formula of the compound?

Accepted Answer

$$	ext{K}_2	ext{SO}_4$$

Question 9

Pineapple oil has a molar mass of 116.16 g/mol and contains 62.04% C, 10.41% H, and 27.55% O. What is its molecular formula?

Accepted Answer

$$	ext{C}_6	ext{H}_{12}	ext{O}_2$$

Question 10

Which of the following best describes the relationship between empirical and molecular formulas?

Accepted Answer

The molecular formula is always a whole-number multiple of the empirical formula.

Question 11

A scientist has $$8.323 	imes 10$$^{22}$$ atoms of hydrogen in ammonium phosphate. How many moles of hydrogen atoms does this represent?

Accepted Answer

$$\frac{8.323 	imes 10$$^{22}$$}{6.022 	imes 10$$^{23}$$} = 0.138$$ mol

Question 12

Which sample from the first image would contain the greatest number of atoms?

Accepted Answer

118.7 g Sn

Question 13

A 2.241 g sample of nickel reacts with oxygen to form 2.852 g of the metal oxide. What is the empirical formula of the oxide?

Accepted Answer

$$	ext{NiO}$$

Question 14

Which of the following is NOT a representative particle as described in the mole concept?

Accepted Answer

Gram

Question 15

Silver(I) chloride contains 75.27% silver. How many grams of silver(I) chloride are needed to obtain 4.8 g of silver?

Accepted Answer

$$\frac{4.8}{0.7527} = 6.38 g$$

Question 16

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

Accepted Answer

It allows chemists to count atoms, molecules, or ions by weighing macroscopic amounts.

Chemical Composition and Stoichiometry: Study Notes

Study Guide - Practice Questions