Q: Which of the following statements about Avogadro’s number is correct?

One mole of any substance contains $$6.022 \times 10$$^{23}$$ particles.

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

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

Question 1

Which of the following best describes why coefficients are used to balance chemical equations instead of changing subscripts?

Accepted Answer

Changing subscripts would alter the identity of the substances involved.

Question 2

Which of the following is the correct balanced equation for the combustion of methane ($$\mathrm{CH_4$}) in $$oxygen?

Accepted Answer

$$\mathrm{CH_4$} + 2\mathrm{O_2$} \rightarrow \mathrm{CO_2$} + 2\mathrm{H_2O}$$

Question 3

A student heats $$10.0\ \mathrm{g} of $$calcium carbonate ($$\mathrm{$$CaCO_3$$}). $$What is the theoretical yield of carbon dioxide ($$\mathrm{CO_2$}) $$produced? ($$\mathrm{$$CaCO_3$$} \rightarrow \mathrm{CaO} + \mathrm{CO_2$}$$; molar masses: $$\mathrm{$$CaCO_3$$} = 100.1\ \mathrm{g/mol}$$, $$\mathrm{CO_2$} = 44.0\ \mathrm{g/mol})$$

Accepted Answer

$$4.40\ \mathrm{g}$$

Question 4

Which of the following statements about Avogadro’s number is correct?

Accepted Answer

One mole of any substance contains $$6.022 	imes 10$$^{23}$$ particles.

Question 5

A compound is found to contain $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 6

Which of the following best describes a limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed.

Question 7

If $$2.00\ \mathrm{mol} of $$hydrogen gas reacts with $$1.00\ \mathrm{mol} of $$oxygen gas to form water, what is the limiting reactant? ($$2\mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\mathrm{H_2O})$$

Accepted Answer

Oxygen gas

Question 8

A sample of glucose ($$\mathrm{C_6H_{12}O_6$}) $$weighs $$18.0\ \mathrm{g}. $$How many moles of glucose are present? (Molar mass $$= 180.0\ \mathrm{g/mol})$$

Accepted Answer

$$0.100\ \mathrm{mol}$$

Question 9

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

Accepted Answer

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

Question 10

A reaction has a theoretical yield of $$5.00\ \mathrm{g}$$ and an actual yield of $$4.00\ \mathrm{g}. $$What is the percent yield?

Accepted Answer

$$80.0\%$$

Question 11

Which of the following is a decomposition reaction?

Accepted Answer

$$2\mathrm{$$KClO_3$$} \rightarrow 2\mathrm{KCl} + 3\mathrm{O_2$}$$

Question 12

How many molecules are present in $$0.250\ \mathrm{mol} of $$water?

Accepted Answer

$$1.51 	imes 10$$^{23}$$

Question 13

Which of the following is true about the relationship between empirical and molecular formulas?

Accepted Answer

The molecular formula is a whole-number multiple of the empirical formula.

Question 14

A $$5.00\ \mathrm{g}$$ sample of a compound containing only C, H, and O is combusted, producing $$7.33\ \mathrm{g} of$$ $$\mathrm{CO_2$}$$ and $$3.00\ \mathrm{g} of$$ $$\mathrm{H_2O}. $$What is the mass of oxygen in the original sample?

Accepted Answer

$$0.67\ \mathrm{g}$$

Question 15

Which of the following is a combination reaction?

Accepted Answer

$$2\mathrm{Na} + \mathrm{Cl_2$} \rightarrow 2\mathrm{NaCl}$$

Question 16

What is the formula weight of sulfuric acid ($$\mathrm{H_2SO_4}$$)? (Atomic weights: H = 1.0, S = 32.1, O = 16.0)

Accepted Answer

$$98.1$$

Question 17

Which of the following best describes a combustion reaction?

Accepted Answer

A rapid reaction with oxygen that produces a flame.

Question 18

If $$3.00\ \mathrm{g} of $$copper contains how many atoms? (Atomic mass of Cu = $$63.5\ \mathrm{g/mol}$$, Avogadro’s number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$2.85 	imes 10$$^{22}$$

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