Q: A student is asked to prepare 1.0 L of a 0.25 M NaCl solution. How many grams of NaCl ($$M_{NaCl} = 58.44\ g/mol) $$are required?

$$0.25\ mol \times 58.44\ g/mol = 14.61\ g$$

Q: A reaction requires 28 mmol of $$H_2O. $$How many grams of water is this? ($$M_{H_2O} = 18.02\ g/mol)$$

$$28\ mmol \times \frac{18.02\ g}{1000\ mmol} = 0.50456\ g$$

Q: Which of the following is the correct formula for calculating the molarity ($$M) of a $$solution?

$$M = \frac{\text{moles of solute}}{\text{liters of solution}}$$

Question 1

Which of the following best describes a buffer solution and its primary function in a chemical system?

Accepted Answer

A buffer is a solution that resists changes in pH when small amounts of acid or base are added.

Question 2

Given a buffer solution containing 0.50 mol of acetic acid ($$CH_3COOH) $$and 0.50 mol of sodium acetate ($$CH_3COONa) in 1.0 L of $$solution, what will happen to the pH if 0.01 mol of HCl is added?

Accepted Answer

The pH will decrease only slightly due to the buffer's action.

Question 3

A student is asked to prepare 1.0 L of a 0.25 M NaCl solution. How many grams of NaCl ($$M_{NaCl} = 58.44\ g/mol) $$are required?

Accepted Answer

$$0.25\ mol 	imes 58.44\ g/mol = 14.61\ g$$

Question 4

Which of the following best explains why water ($$H_2O) is $$considered a polar molecule?

Accepted Answer

Water has a bent molecular geometry and an uneven distribution of electron density.

Question 5

A reaction requires 28 mmol of $$H_2O. $$How many grams of water is this? ($$M_{H_2O} = 18.02\ g/mol)$$

Accepted Answer

$$28\ mmol 	imes \frac{18.02\ g}{1000\ mmol} = 0.50456\ g$$

Question 6

Which of the following statements about acids and bases is correct according to the Brønsted-Lowry theory?

Accepted Answer

An acid is a proton donor and a base is a proton acceptor.

Question 7

A solution is prepared by dissolving 23 mmol of a compound in enough water to make 1.0 L of solution. What is the molarity of the solution?

Accepted Answer

$$\frac{23\ mmol}{1000\ mmol/mol} = 0.023\ mol$$, so $$0.023\ M$$

Question 8

Which of the following best describes the process of neutralization?

Accepted Answer

A reaction in which an acid and a base react to form water and a salt.

Question 9

A buffer solution is made by mixing 0.10 mol of $$NH_4Cl$$ and 0.10 mol of $$NH_3 in 1.0 L of $$water. If $$K_b$$ for $$NH_3 is$$ $$1.8 	imes 10^{-5}$$, what is the pH of the buffer? ($$pK_b = -\log K_b$$, $$pK_w = 14$$, $$pH + pOH = 14)$$

Accepted Answer

$$pOH = pK_b + \log \left(\frac{[NH_4^+]}{[NH_3]}\right) = 4.74 + \log(1) = 4.74$$, so $$pH = 14 - 4.74 = 9.26$$

Question 10

Which of the following is the correct formula for calculating the molarity ($$M) of a $$solution?

Accepted Answer

$$M = \frac{	ext{moles of solute}}{	ext{liters of solution}}$$

Question 11

A 250 mL sample of a 0.40 M solution contains how many moles of solute?

Accepted Answer

$$0.40\ M 	imes 0.250\ L = 0.10\ mol$$

Question 12

Which of the following best explains why sodium chloride ($$NaCl) $$dissolves readily in water?

Accepted Answer

The polar water molecules surround and stabilize the $$Na^+$$ and $$Cl^-$$ ions, overcoming the ionic lattice.

Question 13

A solution is labeled as 1.0 M. What does this mean in terms of concentration?

Accepted Answer

There is 1.0 mole of solute per liter of solution.

Question 14

Which of the following is a correct net ionic equation for the neutralization of hydrochloric acid ($$HCl) $$with sodium hydroxide ($$NaOH$$)?

Accepted Answer

$$H^+ (aq) + OH^- (aq) \rightarrow H_2O (l)$$

Question 15

A student mixes 50.0 mL of 0.10 M $$HCl$$ with 50.0 mL of 0.10 M $$NaOH. $$What is the pH of the resulting solution?

Accepted Answer

The solution is neutral, so $$pH = 7.$$

Question 16

Which of the following is the correct relationship between $$pH$$ and $$[H^+]$$ concentration?

Accepted Answer

$$pH = -\log [H^+]$$

Question 17

A solution has a $$[H^+]$$ concentration of $$1.0 	imes 10^{-3} M. $$What is its pH?

Accepted Answer

$$pH = -\log(1.0 	imes 10^{-3}) = 3$$

Question 18

Which of the following best describes the role of a conjugate base in a buffer system?

Accepted Answer

It reacts with added acids to minimize changes in pH.

Question 19

A patient receives an intravenous solution containing 0.9% NaCl (normal saline). What is the primary reason for using this concentration in medical practice?

Accepted Answer

It is isotonic with human blood, preventing cell lysis or crenation.

Quantities in Chemical Reactions and Chemical Composition: Study Notes

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