Q: Which of the following best describes Avogadro’s number and its use in chemistry?

Avogadro’s number is $$6.022 \times 10$$^{23}$$ and is used to convert between moles and number of particles.

Q: Which of the following is the correct setup to convert $$10.0 g of $$NaCl to number of formula units?

$$10.0\ \text{g NaCl} \times \frac{1\ \text{mol NaCl}}{58.44\ \text{g NaCl}} \times \frac{6.022 \times 10$$^{23}$$\ \text{units}}{1\ \text{mol NaCl}}$$

Q: How many atoms are present in $$2.00$$ moles of magnesium?

$$1.20 \times 10$$^{24}$$ atoms

Q: Which conversion factor would you use to convert from moles of a substance to number of particles?

$$\frac{6.022 \times 10$$^{23}$$\ \text{particles}}{1\ \text{mol}}$$

Question 1

Which of the following best describes Avogadro’s number and its use in chemistry?

Accepted Answer

Avogadro’s number is $$6.022 	imes 10$$^{23}$$ and is used to convert between moles and number of particles.

Question 2

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of CO_2$. How many moles of CO_2$ are present?

Accepted Answer

$$0.500$$ mol

Question 3

What is the molar mass of calcium nitrate, Ca(NO$$_3$$)$$_2$$?

Accepted Answer

$$164.10 g/$$mol

Question 4

Which of the following is the correct setup to convert $$10.0 g of $$NaCl to number of formula units?

Accepted Answer

$$10.0\ 	ext{g NaCl} 	imes \frac{1\ 	ext{mol NaCl}}{58.44\ 	ext{g NaCl}} 	imes \frac{6.022 	imes 10$$^{23}$$\ 	ext{units}}{1\ 	ext{mol NaCl}}$$

Question 5

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

CH$$_2O$$

Question 6

If the empirical formula of a compound is CH$$_2$$ and its molar mass is 56 g/mol, what is its molecular formula?

Accepted Answer

C$$_4H$_8$$

Question 7

A $$25.0 g $$sample of a compound contains $$10.0 g of $$nitrogen. What is the percent composition of nitrogen in the compound?

Accepted Answer

$$40.0\%$$

Question 8

Which of the following statements about empirical and molecular formulas is correct?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms, while the molecular formula shows the actual number of atoms in a molecule.

Question 9

A sample of iron oxide contains $$69.94 g Fe $$and $$30.06 g O. $$What is the empirical formula of the compound?

Accepted Answer

Fe$$_2O$_3$$

Question 10

How many atoms are present in $$2.00$$ moles of magnesium?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 11

Which of the following is the correct percent composition by mass of hydrogen in H$$_2O$$?

Accepted Answer

$$11.2\%$$

Question 12

A compound has an empirical formula of NO$$_2$$ and a molar mass of $$92.0 g/$$mol. What is its molecular formula?

Accepted Answer

N$$_2O$_4$$

Question 13

Which conversion factor would you use to convert from moles of a substance to number of particles?

Accepted Answer

$$\frac{6.022 	imes 10$$^{23}$$\ 	ext{particles}}{1\ 	ext{mol}}$$

Question 14

A $$50.0 g $$sample of glucose (C$$_6H$_{12}O$_6) $$contains how many moles of glucose? (Molar mass = $$180.16 g/$$mol)

Accepted Answer

$$0.278$$ mol

Question 15

Which of the following best describes the process for determining an empirical formula from percent composition data?

Accepted Answer

Convert percent to grams, grams to moles, divide by smallest number of moles, and adjust to whole numbers.

Mole Quantities, Percent Composition, and Empirical/Molecular Formulas

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