Q: What is the percent composition of carbon in glucose ($$C_6H_{12}O_6$)? (C = 12.0 amu, H = 1.0 amu, O = 16.0 amu)

$$\frac{6 \times 12.0}{180.0} \times 100 = 40.0\%$$

Q: How many molecules are present in 2.00 moles of $$H_2O$$?

$$2.00 \times 6.02 \times 10$$^{23}$$ = 1.20 \times 10$$^{24}$$ molecules

Q: A sample contains 3.0 g of copper (Cu). How many atoms of Cu are present? (Atomic mass of Cu = 63.5 g/mol, Avogadro’s number = $$6.02 \times 10$$^{23}$$)

$$\frac{3.0}{63.5} \times 6.02 \times 10$$^{23}$$ = 2.85 \times 10$$^{22}$$ atoms

Q: In a combustion analysis, a 1.00 g sample of a compound containing C, H, and O produces 1.47 g $$CO_2$$ and 0.60 g $$H_2O. $$What is the mass of carbon in the sample? (Molar mass $$CO_2 = 44.0 g/$$mol, C = 12.0 g/mol)

$$\frac{1.47}{44.0} \times 12.0 = 0.401 g$$

Question 1

Which statement best describes the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 2

Which of the following is the correct balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 3

A student heats $$CaCO_3(s$$)$$ and collects the gas produced. Which type of reaction is this, and what are the products?

Accepted Answer

Decomposition reaction; $$CaO(s)$$ and $$CO_2(g$$)$$

Question 4

Which of the following best describes a combination reaction?

Accepted Answer

Two or more reactants combine to form a single product.

Question 5

Calculate the formula weight of $$H_2SO_4$$ using the following atomic weights: H = 1.0 amu, S = 32.1 amu, O = 16.0 amu.

Accepted Answer

$$2(1.0) + 1(32.1) + 4(16.0) = 98.1$$ amu

Question 6

What is the percent composition of carbon in glucose ($$C_6H_{12}O_6$)? (C = 12.0 amu, H = 1.0 amu, O = 16.0 amu)

Accepted Answer

$$\frac{6 	imes 12.0}{180.0} 	imes 100 = 40.0\%$$

Question 7

How many molecules are present in 2.00 moles of $$H_2O$$?

Accepted Answer

$$2.00 	imes 6.02 	imes 10$$^{23}$$ = 1.20 	imes 10$$^{24}$$ molecules

Question 8

A sample contains 3.0 g of copper (Cu). How many atoms of Cu are present? (Atomic mass of Cu = 63.5 g/mol, Avogadro’s number = $$6.02 	imes 10$$^{23}$$)

Accepted Answer

$$\frac{3.0}{63.5} 	imes 6.02 	imes 10$$^{23}$$ = 2.85 	imes 10$$^{22}$$ atoms

Question 9

A compound is found to contain 61.31% C, 5.14% H, 10.21% N, and 23.33% O by mass. What is its empirical formula?

Accepted Answer

$$C_7H_7NO_2$$

Question 10

A compound has an empirical formula of CH and a molar mass of 78 g/mol. What is its molecular formula?

Accepted Answer

$$C_6H_6$$

Question 11

In a combustion analysis, a 1.00 g sample of a compound containing C, H, and O produces 1.47 g $$CO_2$$ and 0.60 g $$H_2O. $$What is the mass of carbon in the sample? (Molar mass $$CO_2 = 44.0 g/$$mol, C = 12.0 g/mol)

Accepted Answer

$$\frac{1.47}{44.0} 	imes 12.0 = 0.401 g$$

Question 12

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

Accepted Answer

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

Question 13

If 4.0 g of $$H_2$$ reacts with 32.0 g of $$O_2 to $$form $$H_2O$$, what is the theoretical yield of $$H_2O in $$grams? ($$2H_2 + O_2$ \rightarrow 2H_2O$$; molar masses: $$H_2 = 2.0$ g/mol, O_2$ = 32.0 g/$$mol, $$H_2O = 18.0 g/$$mol)

Accepted Answer

36.0 g

Question 14

A reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is actually obtained. What is the percent yield?

Accepted Answer

$$\frac{7.5}{10.0} 	imes 100 = 75\%$$

Question 15

Which of the following is true about the coefficients in a balanced chemical equation?

Accepted Answer

They represent the relative numbers of molecules and moles of reactants and products.

Question 16

Which of the following is a correct sequence for converting grams of a substance to the number of formula units?

Accepted Answer

Grams $$\rightarrow$$ Moles $$\rightarrow$$ Avogadro's number $$\rightarrow$$ Formula units

Chemical Reactions and Reaction Stoichiometry: Study Notes

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