Q: A student wants to prepare 250 mL of a 0.5 M NaCl solution. What mass of NaCl is required? ($M = \frac{\text{mol}}{\text{L}}$; molar mass NaCl = 58.5 g/mol)

$0.5 \times 0.25 \times 58.5 = 7.31$ g

Q: How many molecules are present in 2 moles of $CO_2$? ($N_A = 6.022 \times 10^{23}$)

$2 \times 6.022 \times 10^{23} = 1.2044 \times 10^{24}$ molecules

Q: A solution is prepared by dissolving 25.5 g NaCl in 425 g water. What is the percent by mass of NaCl in the solution?

$\frac{25.5}{25.5 + 425} \times 100 = 5.7\%$

Q: If 2 mol of $H_2$ react with 1 mol of $O_2$ to produce water, how many grams of $H_2O$ are formed? (Molar mass $H_2O = 18$ g/mol)

$2 \text{ mol} \times 18 \text{ g/mol} = 36$ g

Question 1

Which of the following best describes the role of coefficients in a balanced chemical equation?

Accepted Answer

They represent the ratio of reactants and products involved in the reaction.

Question 2

According to Avogadro's Hypothesis, which of the following statements is correct?

Accepted Answer

Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Question 3

A student wants to prepare 250 mL of a 0.5 M NaCl solution. What mass of NaCl is required? ($M = \frac{	ext{mol}}{	ext{L}}$; molar mass NaCl = 58.5 g/mol)

Accepted Answer

$0.5 	imes 0.25 	imes 58.5 = 7.31$ g

Question 4

Which of the following is the correct balanced equation for the combustion of propane ($C_3H_8$) in oxygen?

Accepted Answer

$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$

Question 5

How many molecules are present in 2 moles of $CO_2$? ($N_A = 6.022 	imes 10^{23}$)

Accepted Answer

$2 	imes 6.022 	imes 10^{23} = 1.2044 	imes 10^{24}$ molecules

Question 6

A solution is prepared by dissolving 25.5 g NaCl in 425 g water. What is the percent by mass of NaCl in the solution?

Accepted Answer

$\frac{25.5}{25.5 + 425} 	imes 100 = 5.7\%$

Question 7

Which of the following statements about stoichiometry is correct?

Accepted Answer

Stoichiometry is used to calculate the mass of reactants and products in a chemical reaction.

Question 8

If 2 mol of $H_2$ react with 1 mol of $O_2$ to produce water, how many grams of $H_2O$ are formed? (Molar mass $H_2O = 18$ g/mol)

Accepted Answer

$2 	ext{ mol} 	imes 18 	ext{ g/mol} = 36$ g

Question 9

Which of the following is NOT a correct step in solving a stoichiometry problem?

Accepted Answer

Change subscripts in chemical formulas to balance atoms.

Question 10

A chemist needs to prepare 430 g of a 4.85% NaOH solution by mass. How many grams of NaOH are required?

Accepted Answer

$430 	imes 0.0485 = 20.9$ g

Question 11

Which of the following best describes a solute in a solution?

Accepted Answer

The substance that is dissolved.

Question 12

What is the molarity of a solution containing 3.50 mol NaCl in 2.00 L of solution?

Accepted Answer

$\frac{3.50}{2.00} = 1.75$ M

Question 13

Which of the following is the correct formula for percent by volume?

Accepted Answer

$\frac{	ext{volume solute}}{	ext{total volume}} 	imes 100$

Question 14

If you have 1 mole of $O_2$ gas at STP, what is its volume?

Accepted Answer

$22.4$ L

Question 15

Which of the following is a correct statement about mass conservation in chemical reactions?

Accepted Answer

Mass is conserved in every chemical reaction.

Question 16

A chemical equation is balanced when:

Accepted Answer

The number of atoms of each element is the same on both sides of the equation.

Question 17

Which of the following is the correct formula for converting mass to moles?

Accepted Answer

$	ext{Moles} = \frac{	ext{Mass (g)}}{	ext{Molar Mass (g/mol)}}$

Question 18

A solution contains 120 mL of ethanol in 4.0 L of fuel. What is the percent by volume of ethanol?

Accepted Answer

$\frac{120}{4000} 	imes 100 = 3.0\%$

Question 19

Which of the following is NOT a way to describe concentration in solutions?

Accepted Answer

Density

Chemical Accounting: Chapter 5 Study Notes

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