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

$$\frac{\text{mass of element in 1 mol compound}}{\text{molar mass of compound}} \times 100\%$$

Question 1

The FDA recommends consuming less than 2.3 g of sodium per day. If sodium chloride (NaCl) is 39% sodium by mass, what is the maximum mass of NaCl you can consume in a day and still stay within the FDA sodium guideline?

Accepted Answer

$$5.9\ \mathrm{g}$$

Question 2

Which of the following statements about the mole is correct?

Accepted Answer

A mole of any element contains $$6.022\$$times10^{23}$$ atoms.

Question 3

How many aluminum atoms are present in a $$16.2\ \mathrm{g}$$ aluminum can? (Molar mass of Al = $$26.98\ \mathrm{g/mol})$$

Accepted Answer

$$3.61\$$times10^{23}$$ atoms

Question 4

What is the mass percent of chlorine in carbon tetrachloride ($$\mathrm{$$CCl_4$$}$$)? (Atomic masses: C = $$12.01$$, Cl = $$35.45)$$

Accepted Answer

$$92.20\%$$

Question 5

A sample of a compound contains $$3.0\ \mathrm{g} of $$hydrogen and $$24.0\ \mathrm{g} of $$oxygen. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{H_2O}$$

Question 6

If you have $$1.75\ \mathrm{mol} of $$water ($$\mathrm{H_2O}$$), what is its mass in grams? (Molar mass of $$\mathrm{H_2O}$$ = $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$31.5\ \mathrm{g}$$

Question 7

Which conversion factor would you use to convert from moles of a compound to grams of that compound?

Accepted Answer

Molar mass of the compound

Question 8

A $$0.58\ \mathrm{g}$$ diamond is pure carbon. How many moles of carbon does it contain? (Molar mass of C = $$12.01\ \mathrm{g/mol})$$

Accepted Answer

$$4.8\$$times10^{-2}$$\ \mathrm{mol}$$

Question 9

What is the empirical formula of a compound that is $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 10

A compound has an empirical formula of $$\mathrm{CH_2O}$$ and a molar mass of $$180.2\ \mathrm{g/mol}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$}$$

Question 11

How many moles of oxygen atoms are present in $$1.7\ \mathrm{mol} of$$ $$\mathrm{$$CaCO_3$$}$$?

Accepted Answer

$$5.1\ \mathrm{mol}$$

Question 12

What is the mass of sodium in $$15\ \mathrm{g} of $$sodium chloride ($$\mathrm{NaCl}$$)? (Molar mass Na = $$22.99\ \mathrm{g/mol}$$, NaCl = $$58.44\ \mathrm{g/mol})$$

Accepted Answer

$$5.9\ \mathrm{g}$$

Question 13

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 14

A $$0.523\ \mathrm{g}$$ sample of a chromium oxide contains $$0.358\ \mathrm{g} of $$chromium. What is the mass percent of chromium in the oxide?

Accepted Answer

$$68.5\%$$

Question 15

If you have $$4.78\$$times10^{22}$$ molecules of $$\mathrm{$$NO_2$$}$$, what is the mass in grams? (Molar mass of $$\mathrm{$$NO_2$$}$$ = 46.01$$\ \mathrm{g/mol}$$)

Accepted Answer

$$3.65\ \mathrm{g}$$

Question 16

What is the mass percent of fluorine in sodium fluoride ($$\mathrm{NaF}$$)? (Na = $$22.99$$, F = $$19.00)$$

Accepted Answer

$$45.25\%$$

Question 17

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

Accepted Answer

$$\frac{	ext{mass of element in 1 mol compound}}{	ext{molar mass of compound}} 	imes 100\%$$

Question 18

A compound is found to contain $$70.0\%$$ iron and $$30.0\%$$ oxygen by mass. What is the empirical formula? (Fe = $$55.85$$, O = $$16.00)$$

Accepted Answer

$$\mathrm{Fe_2O_3}$$

Chemical Composition and Calculations in Introductory Chemistry (Chapter 6 Study Notes)

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