Q: What is the formula mass (in g/mol) of $$\mathrm{Ca(NO_3$)_2}$$? (Atomic masses: Ca = 40.08, N = 14.01, O = 16.00)

$$40.08 + 2 \times (14.01 + 3 \times 16.00) = 164.10\ \mathrm{g/mol}$$

Q: A sample contains $$2.7\ \mathrm{mol} of$$ $$\mathrm{CO_2$}. $$What is the mass of this sample in grams? (Molar mass of $$\mathrm{CO_2$} = 44.01\ \mathrm{g/mol})$$

$$2.7 \times 44.01 = 118.83\ \mathrm{g}$$

Q: What is the mass percent of oxygen in acetic acid ($$\mathrm{C_2H_4O_2}$$)? (Atomic masses: C = 12.01, H = 1.01, O = 16.00)

$$\frac{2 \times 16.00}{60.05} \times 100 = 53.28\%$$

Q: A tablet contains $$200.0\ \mathrm{mg} of $$ibuprofen ($$\mathrm{C$$_{13}$$H_{18}O_2$}). $$How many molecules of ibuprofen are present? (Molar mass = $$206.285\ \mathrm{g/mol}$$, $$N_A = 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$\frac{0.2000}{206.285} \times 6.022 \times 10$$^{23}$$ = 5.83 \times 10$$^{20}$$ molecules

Q: Calculate the mass percent composition of sodium in sodium oxide ($$\mathrm{Na_2O}). ($$Atomic masses: Na = 22.99, O = 16.00)

$$\frac{2 \times 22.99}{2 \times 22.99 + 16.00} \times 100 = 79.12\%$$

Q: If a person consumes $$22\ \mathrm{g} of $$sodium chloride per day, how many grams of sodium does this person consume? (Sodium chloride is 39% sodium by mass)

$$22 \times 0.39 = 8.6\ \mathrm{g}$$

Q: A sample of water contains $$3.55 \times 10$$^{24}$$ molecules. What is the mass of this sample in grams? (Molar mass of $$\mathrm{H_2O} = 18.015\ \mathrm{g/mol}$$, N_A = 6.022$$ \times $$10^{23}$$\ \mathrm{mol}^{-1}$$)

$$\frac{3.55 \times 10$$^{24}$$}{6.022 \times 10$$^{23}$$} \times 18.015 = 106.1\ \mathrm{g}$$

Question 1

Which of the following correctly gives the number of each type of atom in the compound $$\mathrm{Mg_3$(PO_4$)_2}$$?

Accepted Answer

Mg: 3, P: 2, O: 8

Question 2

What is the formula mass (in g/mol) of $$\mathrm{Ca(NO_3$)_2}$$? (Atomic masses: Ca = 40.08, N = 14.01, O = 16.00)

Accepted Answer

$$40.08 + 2 	imes (14.01 + 3 	imes 16.00) = 164.10\ \mathrm{g/mol}$$

Question 3

A sample contains $$2.7\ \mathrm{mol} of$$ $$\mathrm{CO_2$}. $$What is the mass of this sample in grams? (Molar mass of $$\mathrm{CO_2$} = 44.01\ \mathrm{g/mol})$$

Accepted Answer

$$2.7 	imes 44.01 = 118.83\ \mathrm{g}$$

Question 4

What is the mass percent of oxygen in acetic acid ($$\mathrm{C_2H_4O_2}$$)? (Atomic masses: C = 12.01, H = 1.01, O = 16.00)

Accepted Answer

$$\frac{2 	imes 16.00}{60.05} 	imes 100 = 53.28\%$$

Question 5

A tablet contains $$200.0\ \mathrm{mg} of $$ibuprofen ($$\mathrm{C$$_{13}$$H_{18}O_2$}). $$How many molecules of ibuprofen are present? (Molar mass = $$206.285\ \mathrm{g/mol}$$, $$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$\frac{0.2000}{206.285} 	imes 6.022 	imes 10$$^{23}$$ = 5.83 	imes 10$$^{20}$$ molecules

Question 6

Calculate the mass percent composition of sodium in sodium oxide ($$\mathrm{Na_2O}). ($$Atomic masses: Na = 22.99, O = 16.00)

Accepted Answer

$$\frac{2 	imes 22.99}{2 	imes 22.99 + 16.00} 	imes 100 = 79.12\%$$

Question 7

If a person consumes $$22\ \mathrm{g} of $$sodium chloride per day, how many grams of sodium does this person consume? (Sodium chloride is 39% sodium by mass)

Accepted Answer

$$22 	imes 0.39 = 8.6\ \mathrm{g}$$

Question 8

A sample of water contains $$3.55 	imes 10$$^{24}$$ molecules. What is the mass of this sample in grams? (Molar mass of $$\mathrm{H_2O} = 18.015\ \mathrm{g/mol}$$, N_A = 6.022$$ 	imes $$10^{23}$$\ \mathrm{mol}^{-1}$$)

Accepted Answer

$$\frac{3.55 	imes 10$$^{24}$$}{6.022 	imes 10$$^{23}$$} 	imes 18.015 = 106.1\ \mathrm{g}$$

Question 9

Which of the following steps is NOT necessary when calculating the formula mass of a compound?

Accepted Answer

Dividing the total mass by Avogadro's number

Question 10

A $$128\ \mathrm{kg}$$ sample of carbon tetrabromide ($$\mathrm{$$CBr_4$$}) is $$used in an industrial process. How many moles of $$\mathrm{$$CBr_4$$}$$ are present? (Molar mass = $$331.63\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{128,000}{331.63} = 386.0\ \mathrm{mol}$$

Question 11

Which of the following best describes the process for finding the mass percent of an element in a compound?

Accepted Answer

Divide the total mass of the element in one mole of the compound by the molar mass of the compound, then multiply by 100

Question 12

A $$112.7\ \mathrm{mmol}$$ sample of sulfur hexafluoride ($$\mathrm{SF_6$}) is $$used in a laboratory. What is the mass of this sample in grams? (Molar mass = $$146.06\ \mathrm{g/mol})$$

Accepted Answer

$$0.1127 	imes 146.06 = 16.46\ \mathrm{g}$$

Question 13

Which of the following is the correct formula mass for $$\mathrm{H_2SO_4}$$? (Atomic masses: H = 1.01, S = 32.07, O = 16.00)

Accepted Answer

$$2 	imes 1.01 + 32.07 + 4 	imes 16.00 = 98.09\ \mathrm{g/mol}$$

Question 14

A $$38.6\ \mathrm{g}$$ sample of nitrogen dioxide ($$\mathrm{NO_2$}) $$contains how many moles? (Molar mass = $$46.01\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{38.6}{46.01} = 0.839\ \mathrm{mol}$$

Question 15

Which of the following best explains why the mass percent of sodium in sodium chloride is less than 50%?

Accepted Answer

Chlorine has a much higher atomic mass than sodium, so it contributes more to the total mass of the compound

Question 16

If you have $$41.009\ \mathrm{g} of$$ $$\mathrm{CO_2$}$$, how many moles of $$\mathrm{CO_2$} do $$you have? (Molar mass = $$44.01\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{41.009}{44.01} = 0.932\ \mathrm{mol}$$

Formula Mass and Mass Percent Composition

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드