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

$$\frac{2 \times 16}{14 + 2 \times 16} \times 100\%$$

Question 1

Which of the following best describes the term 'mass percent' in the context of a chemical compound?

Accepted Answer

The percentage of the total mass of a compound that is contributed by a specific element.

Question 2

Given the formula for mass percent: $$	ext{Mass Percent} = \frac{	ext{grams element}}{	ext{grams compound}} 	imes 100\%$$, what is the mass percent of sodium in sodium carbonate ($$\mathrm{Na_2CO_3}$$)? (Molar masses: Na = 23 g/mol, C = 12 g/mol, O = 16 g/mol)

Accepted Answer

$$\approx 43.4\%$$

Question 3

A student calculates the mass percent of carbon in $$\mathrm{Na_2CO_3} as$$ $$11.3\%. $$Which of the following best explains the steps they should have taken?

Accepted Answer

Divide the mass of carbon in one mole of $$\mathrm{Na_2CO_3} by $$the total molar mass of $$\mathrm{Na_2CO_3}$$, then multiply by 100%.

Question 4

Which of the following is the correct mass percent of nitrogen in nitrogen dioxide ($$\mathrm{NO_2$}$$)? (Molar masses: N = 14 g/mol, O = 16 g/mol)

Accepted Answer

$$30.4\%$$

Question 5

If a compound has a mass percent of oxygen of $$53.3\%$$, which of the following could be the compound? (Molar masses: N = 14 g/mol, O = 16 g/mol)

Accepted Answer

$$\mathrm{NO_2$}$$

Question 6

A chemist needs to prepare 100 g of a compound that is $$30\%$$ carbon by mass. How many grams of carbon are required?

Accepted Answer

$$30 g$$

Question 7

Which of the following statements about mass percent is FALSE?

Accepted Answer

Mass percent changes if the amount of compound changes.

Question 8

A sample of $$\mathrm{Na_2CO_3}$$ weighs 53 g. How many grams of carbon are present in the sample? (Molar mass of $$\mathrm{Na_2CO_3} = 106 g/$$mol)

Accepted Answer

$$6.0 g$$

Question 9

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

Accepted Answer

$$\frac{2 	imes 16}{14 + 2 	imes 16} 	imes 100\%$$

Question 10

A patient is given a medication containing 250 mg of a compound that is $$40\%$$ active ingredient by mass. How many milligrams of the active ingredient does the patient receive?

Accepted Answer

$$100 mg$$

Question 11

If the mass percent of sodium in $$\mathrm{Na_2CO_3} is$$ $$43.4\%$$, what is the mass of sodium in a 25 g sample of $$\mathrm{Na_2CO_3}$$?

Accepted Answer

$$10.85 g$$

Question 12

Which of the following best explains why mass percent is useful in the medical field?

Accepted Answer

It allows precise calculation of the amount of an active ingredient in a medication.

Question 13

A compound contains $$20 g of $$element X and $$80 g of $$element Y. What is the mass percent of element X?

Accepted Answer

$$25\%$$

Question 14

Which of the following is the correct mass percent of oxygen in $$\mathrm{NO_2$}$$? (Molar masses: N = 14 g/mol, O = 16 g/mol)

Accepted Answer

$$53.3\%$$

Question 15

A 10 g sample of a compound contains 2 g of hydrogen. What is the mass percent of hydrogen in the compound?

Accepted Answer

$$20\%$$

Calculating Mass Percent in Chemical Compounds

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