Q: Which formula is used to calculate the mass percent of an element in a compound?

$$\frac{\text{mass of element}}{\text{mass of compound}} \times 100\%$$

Q: If the molar mass of $$\mathrm{Na_2CO_3} is$$ $$106.0\ \mathrm{g/mol}$$, what is the mass percent of sodium in $$\mathrm{Na_2CO_3}$$? (Atomic mass of Na = $$23.0\ \mathrm{g/mol})$$

$$\frac{46.0}{106.0} \times 100\% = 43.4\%$$

Q: A chemist wants to find the mass percent of oxygen in $$\mathrm{NO_2$}. $$What is the correct calculation? (Atomic mass: N = $$14.01\ \mathrm{g/mol}$$, O = $$16.00\ \mathrm{g/mol})$$

$$\frac{32.00}{46.01} \times 100\% = 69.5\%$$

Q: Which calculation would you use to find the mass percent of nitrogen in $$\mathrm{NO_2$}$$?

$$\frac{14.01}{46.01} \times 100\%$$

Question 1

Which formula is used to calculate the mass percent of an element in a compound?

Accepted Answer

$$\frac{	ext{mass of element}}{	ext{mass of compound}} 	imes 100\%$$

Question 2

A student calculates the mass percent of carbon in sodium carbonate ($$\mathrm{Na_2CO_3}) $$and gets 11.3%. What is the mass of carbon in one mole of $$\mathrm{Na_2CO_3}$$?

Accepted Answer

$$12.01\ \mathrm{g}$$

Question 3

If the molar mass of $$\mathrm{Na_2CO_3} is$$ $$106.0\ \mathrm{g/mol}$$, what is the mass percent of sodium in $$\mathrm{Na_2CO_3}$$? (Atomic mass of Na = $$23.0\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{46.0}{106.0} 	imes 100\% = 43.4\%$$

Question 4

Which of the following best describes mass percent composition?

Accepted Answer

The ratio of the mass of each element to the total mass of the compound, expressed as a percentage.

Question 5

A chemist wants to find the mass percent of oxygen in $$\mathrm{NO_2$}. $$What is the correct calculation? (Atomic mass: N = $$14.01\ \mathrm{g/mol}$$, O = $$16.00\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{32.00}{46.01} 	imes 100\% = 69.5\%$$

Question 6

Why is it important to use the molar mass of the entire compound when calculating mass percent?

Accepted Answer

It ensures the percent reflects the contribution of the element to the whole compound.

Question 7

A sample of $$\mathrm{NO_2$}$$ weighs $$92.02\ \mathrm{g}. $$How many grams of oxygen are present in the sample?

Accepted Answer

$$63.98\ \mathrm{g}$$

Question 8

Which of the following is a common mistake when calculating mass percent composition?

Accepted Answer

Using the atomic mass of the element instead of the total mass of the compound in the denominator.

Question 9

If a compound contains 40% carbon by mass, how many grams of carbon are in a $$50\ \mathrm{g}$$ sample?

Accepted Answer

$$20\ \mathrm{g}$$

Question 10

A medication contains $$\mathrm{Na_2CO_3} as an $$active ingredient. If a tablet contains $$212\ \mathrm{mg} of$$ $$\mathrm{Na_2CO_3}$$, how many milligrams of carbon does it contain?

Accepted Answer

$$23.96\ \mathrm{mg}$$

Question 11

Which real-world scenario best illustrates the importance of mass percent composition?

Accepted Answer

Determining the nutritional content of food based on its chemical composition.

Question 12

A student is given a $$100\ \mathrm{g}$$ sample of $$\mathrm{NO_2$}. $$How many grams of nitrogen are present?

Accepted Answer

$$30.4\ \mathrm{g}$$

Question 13

If the mass percent of oxygen in $$\mathrm{NO_2$} is$$ $$69.5\%$$, what is the mass of oxygen in a $$250\ \mathrm{g}$$ sample?

Accepted Answer

$$173.75\ \mathrm{g}$$

Question 14

Which calculation would you use to find the mass percent of nitrogen in $$\mathrm{NO_2$}$$?

Accepted Answer

$$\frac{14.01}{46.01} 	imes 100\%$$

Question 15

A forensic scientist analyzes a white powder and determines it is $$\mathrm{Na_2CO_3}. $$What percent of the powder's mass is due to sodium?

Accepted Answer

$$43.4\%$$

Mass Percent Composition in Chemical Compounds

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