# 15.E: Exercises

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#### 15.4:  Acids and Bases Defined

1. Write equations showing H2PO4 acting as both a Brønsted-Lowry acid and as a base with water.

acid:  H2PO4 + H2O ⇌ HPO42− + H3O+; base:  H2PO4 + H2O ⇌ H3PO4 + OH

1. Write the equation for the chemical reaction that occurs when caffeine (C8H10N4O2) acts as a Brønsted-Lowry base in water.

C8H10N4O2 + H2O ⇌ HC8H10N4O2+ + OH

1. Citric acid (C6H8O7) is the acid found in citrus fruits. It can lose a maximum of three H+ ions in the presence of a base. Write the chemical equations for citric acid acting stepwise as a Brønsted-Lowry acid in water.

C6H8O7 + H2O ⇌ C6H7O7 + H3O+; C6H7O7 + H2O ⇌ C6H6O72− + H3O+; C6H6O72− + H2O ⇌ C6H5O73− + H3O+

1. What is the conjugate acid of each of the following?
1. OH
2. H2O
3. HCO3
4. NH3
5. HSO4
6. H4N2
1. H2O
2. H3O+
3. H2CO3
4. NH4+
5. H2SO4
6. H5N2+

1. What is the conjugate base of each of the following?
1. H2PO4
2. HS
3. H3O2+
4. H4N2
5. H2S
6. CH3OH
1. HPO42−
2. S2−
3. H2O2
4. H3N2
5. HS
6. CH3O

1. Identify and label the Brønsted-Lowry acid, its conjugate base, the Brønsted-Lowry base, and its conjugate acid in each of the following equations:
1. HNO3 + H2O ⇌ H3O+ + NO3
2. CN + H2O ⇌ HCN + OH
3. H2SO4 + Cl ⇌ HCl + HSO4
4. HSO4 + OH ⇌ SO42 + H2O
1. BL acid = HNO3; conjugate base = NO3; BL base = H2O; conjugate acid = H3O+
2. BL acid = H2O; conjugate base = OH; BL base = CN; conjugate acid = HCN
3. BL acid = H2SO4; conjugate base = HSO4; BL base = Cl; conjugate acid = HCl
4. BL acid = HSO4; conjugate base = SO42−; BL base = OH; conjugate acid = H2O

1. Identify and label the Brønsted-Lowry acid, its conjugate base, the Brønsted-Lowry base, and its conjugate acid in each of the following equations:
1. NO2 + H2O ⇌ HNO2 + OH
2. HBr + H2O ⇌ H3O+ + Br
3. HS + H2O ⇌ H2S + OH
4. H2PO4 + HCl ⇌ H3PO4 + Cl
1. BL acid = H2O; conjugate base = OH; BL base = NO2; conjugate acid = HNO2
2. BL acid = HBr; conjugate base = Br; BL base = H2O; conjugate acid = H3O+
3. BL acid = H2O; conjugate base = OH; BL base = HS; conjugate acid = H2S
4. BL acid = HCl; conjugate base = Cl; BL base = H2PO4; conjugate acid = H3PO4

#### 15.5:  Strong and Weak Acids and Bases

1. Identify each of the following acids or bases as strong or weak:
1. HC2H3O2
2. Ba(OH)2
3. HClO4
4. CH3NH2
1. weak acid
2. strong base
3. strong acid
4. weak base

1. Identify each of the following acids or bases as strong or weak:
1. NaOH
2. C17H21NO4 (cocaine)
3. H2SO3
4. HBr
1. strong base
2. weak base
3. weak acid
4. strong acid

#### 15.6:  Water as an Acid and as a Base

1. Are the concentrations of hydronium ion and hydroxide ion in a solution of an acid or a base in water directly proportional or inversely proportional? Explain.

Inversely proportional. As the concentration of one increases, the concentration of the other will decrease.

1. The hydronium ion concentration in a sample of rainwater is found to be 1.7 × 10−6 M. What is the concentration of hydroxide ions in the rainwater?

[OH] = 5.9 × 10−9 M

1. The hydroxide ion concentration in household ammonia is 3.2 × 10−3 M. What is the concentration of hydronium in the solution?

[H3O+] = 3.1 × 10−12 M

1. Calculate the hydroxide ion concentration for each of the following solutions. Is the solution acidic, basic, or neutral?
1. [H3O+] = 3.5 × 10−4 M
2. [H3O+] = 8.1 × 10−8 M
3. [H3O+] = 7.0 × 10−3 M
1. [OH] = 2.9 × 10−11 M; acidic
2. [OH] = 1.2 × 10−7 M; basic
3. [OH] = 1.4 × 10−12 M; acidic

1. Calculate the hydronium ion concentration for each of the following solutions. Is the solution acidic, basic, or neutral?
1. [OH] = 1.0 × 10−7 M
2. [OH] = 9.3 × 10−11 M
3. [OH] = 2.5 × 10−2 M
1. [H3O+] = 1.0 × 10−7 M; neutral
2. [H3O+] = 1.1 × 10−4 M; acidic
3. [H3O+] = 4.0 × 10−13 M; basic

1. Calculate the hydronium and hydroxide ion concentrations of the following solutions:
1. 0.200 M HCl
2. 0.0143 M NaOH
3. 3.0 M HNO3
4. 0.0031 M Ca(OH)2
1. [H3O+] = 0.200 M; [OH] = 5.0 × 10−14 M
2. [H3O+] = 6.99 × 10−13 M; [OH] = 0.0143 M
3. [H3O+] = 3.0 M; [OH] = 3.3 × 10−15 M
4. [H3O+] = 1.6 × 10−12 M; [OH] = 0.0062 M

1. Calculate the hydronium and hydroxide ion concentrations of each of the following solutions:
1. 0.000259 M HClO4
2. 0.21 M NaOH
3. 0.000071 M Ba(OH)2
4. 2.5 M KOH
1. [H3O+] = 0.000259 M; [OH] = 3.86 × 10−11 M
2. [H3O+] = 4.8 × 10−14 M; [OH] = 0.21 M
3. [H3O+] = 7.1 × 10−11 M; [OH] = 0.00014 M
4. [H3O+] = 4.0 ×10−15 M; [OH] = 2.5 M

#### 15.7:  An Introduction to pH

1. Identify each of the following solutions as acidic, basic, or neutral.
1. pH = 8.2 (baking soda)
2. pH = 2.54 (vinegar)
3. pH = 9.4 (laundry detergent)
1. basic
2. acidic
3. basic

1. Identify each of the following solutions as acidic, basic, or neutral.
1. pH = 7.44 (human tears)
2. pH = 3.4 (white wine)
3. pH = 4.85 (coffee)
1. basic
2. acidic
3. acidic

1. Normal clean rain has a pH of 5.0 to 5.5. Typical acid rain has a pH of 4.0. How much more acidic is acid rain than normal rain with a pH of 5.0?

One pH unit corresponds to a factor of 10. So typical acid rain is 10 times more acidic than normal rain.

1. When a sparkling water was first opened, it had a pH of 3.7. Tap water was found to have a pH of 6.7. Which water is more basic? How much more basic is it?

The tap water has a higher pH, so it is more basic. The tap water's pH is 3 pH units greater. This means that the tap water is 103 or 1000 times more basic.

#### 15.8:  pH and pOH Calculations

1. What is the pOH range for an acidic solution?

The pOH is greater than 7 for an acidic solution (typically up to 14).

1. What is the pOH range for a basic solution?

The pOH is less than 7 for a basic solution (typically down to 0).

1. Calculate the pH of each solution and classify it as acidic or basic.
1. pOH = 5.18
2. pOH = 9.26
3. pOH = 2.84
1. pH = 8.82; basic
2. pH = 4.74; acidic
3. pH = 11.16; basic

1. Calculate the pOH of each solution and classify it as acidic or basic.
1. pH = 8.31
2. pH = 5.20
3. pH = 7.43
1. pOH = 5.69; basic
2. pOH = 8.80; acidic
3. pOH = 6.57; basic

1. The concentration of commercial HCl is about 12 M. What is its pH and pOH?

pH = −1.08; pOH = 15.08

1. The concentration of concentrated H2SO4 is about 18 M. Assuming only one H+ comes off the H2SO4 molecule, what is its pH and pOH?

pH = −1.26; pOH = 15.26

1. Calculate the pH and pOH of each of the following solutions:
1. 0.200 M HCl
2. 0.0143 M NaOH
3. 3.0 M HNO3
4. 0.0031 M Ca(OH)2
1. pH = 0.699; pOH = 13.301
2. pH = 12.155; pOH = 1.845
3. pH = −0.48; pOH = 14.48
4. pH = 11.79; pOH = 2.21

1. Calculate the pH and pOH of each of the following solutions:
1. 0.000259 M HClO4
2. 0.21 M NaOH
3. 0.000071 M Ba(OH)2
4. 2.5 M KOH
1. pH = 3.587; pOH = 10.413
2. pH = 13.32; pOH = 0.68
3. pH = 10.15; pOH = 3.85
4. pH = 14.40; pOH = −0.40

1. What are the hydronium and hydroxide ion concentrations in a solution whose pH is 6.52?

[H3O+] = 3.0 × 10−7 M; [OH] = 3.3 × 10−8 M

1. What are the hydronium and hydroxide ion concentrations in a solution whose pH is 9.20?

[H3O+] = 6.3 × 10−10 M; [OH] = 1.6 × 10−5 M

1. What are the hydronium and hydroxide ion concentrations in a solution whose pOH is 2.18?

[H3O+] = 1.5 × 10−12 M; [OH] = 6.6 × 10−3 M

#### 15.9:  Reactions of Acids and Bases

1. Write the balanced chemical equation between Zn metal and HCl(aq). The other product is ZnCl2.

Zn(s) + 2 HCl(aq) ⇌ ZnCl2(aq) + H2(g)

1. Write the neutralization reaction in which ZnCl2, also found in Exercise 32, is the salt product.

Zn(OH)2 + 2 HCl ⇌ ZnCl2 + 2 H2O

1. Write the balanced chemical equation between aluminum hydroxide and sulfuric acid.

2 Al(OH)3 + 3 H2SO4 ⇌ Al2(SO4)3 + 6 H2O

1. Write the balanced chemical equation between phosphoric acid and barium hydroxide.

2 H3PO4 + 3 Ba(OH)2 ⇌ Ba3(PO4)2 + 6 H2O

1. Complete and balance the following acid-base reactions:
1. HCl solution reacts with solid Ca(OH)2(s)
2. a solution of Sr(OH)2 is added to a solution of HNO3
1. 2 HCl(aq) + Ca(OH)2(s) ⇌ CaCl2(aq) + 2 H2O(l)
2. Sr(OH)2(aq) + 2 HNO3(aq) ⇌ Sr(NO3)2(aq) + 2 H2O(l)

1. Complete and balance the following acid-base reactions:
1. aqueous H2SO4 reacts with NaOH
2. Ba(OH)2 reacts with HF gas
1. H2SO4(aq) + 2 NaOH(aq) ⇌ Na2SO4(aq) + 2 H2O(l)
2. Ba(OH)2(aq) + 2 HF(g) ⇌ BaF2(aq) + 2 H2O(l)

1. Gastric juice, the digestive fluid produced in the stomach, contains hydrochloric acid, HCl. Milk of Magnesia, a suspension of solid Mg(OH)2 in an aqueous medium, is sometimes used to neutralize excess stomach acid. Write a complete balanced equation for the neutralization reaction.