Acids and Bases

1

UNIT 4: ACIDS & BASES OUTCOMES

All important vocabulary is in Italics and bold.

Outline the historical development of acid base theories.

Include: Arrhenius, Bronsted-Lowry, Lewis.

Write balanced acid/base chemical equations.Include: conjugate acid/base pairs, amphoteric behavior.

Distinguish between strong and weak acids and bases.

Include: electrolytes and non-electrolytes

Describe the relationship between the hydronium and hydroxide ion concentrations in water

Include: the ion product of water, Kw

Formulate an operational definition of pH.

Solve problems involving pH.

Describe how an acid-base indicator works in terms of colour shifts and Le Chatelier’s Principle.

Write the equilibrium expression (Ka or Kb) from a balanced chemical equation.

Use Ka or Kb to solve problems for pH, percent dissociation and concentration.

Predict whether an aqueous solution of a given ionic compound will be acidic, basic or neutral given the

formula.

Write balanced neutralization reactions involving strong acids and bases.

Calculate the concentration or volume of an acid or base from the concentration and volume of an acid or

base required for neutralization.

Using a standardized acid or base, determine the concentration of an unknown base or acid.

Additional KEY Terms

diprotic amphoteric monoprotic

salt hydrolysis concentrated dilute standard solution end point equivalence point

titration

2

Relative Strengths of Acids

*Acids 1.0 mol/L in water at 25ºC

Acid Reaction K a

Perchloric acid HClO4 + H2O → H3O+ + ClO4¯ very large

Hydriodic acid HI + H2O → H3O+ + I¯ very large

Hydrobromic acid HBr + H2O → H3O+ + Br¯ very large

Hydrochloric acid HCl + H2O → H3O+ + Cl¯ very large

Nitric acid HNO3 + H2O → H3O+ + NO3¯ very large

Sulfuric acid H2SO4 + H2O → H3O+ + HSO4¯ very large

Oxalic acid H2C2O4 + H2O → H3O+ + HC2O4¯ 5.4 x 10¯

2

Sulfurous acid H2SO3 + H2O → H3O+ + HSO3¯ 1.7 x 10¯

2

Hydrogen sulfate ion HSO4¯ + H2O → H3O+ + SO4

2¯ 1.3 x 10¯

2

Phosphoric acid H3PO4 + H2O → H3O+ + H2PO4¯ 7.1 x 10¯

3

Ferric ion Fe(H2O)63+

+ H2O → H3O+ + Fe(H2O)5(OH)

2+ 6.0 x 10¯

3

Hydrogen telluride H2Te + H2O → H3O+ + HTe¯ 2.3 x 10¯

3

Hydrofluoric acid HF + H2O → H3O+ + F¯ 6.7 x 10¯

4

Nitrous acid HNO2 + H2O → H3O+ + NO2¯ 5.1 x 10¯

4

Hydrogen selenide H2Se + H2O → H3O+ + HSe¯ 1.7 x 10¯

4

Chromic ion Cr(H2O)63+

+ H2O → H3O+ + Cr(H2O)5(OH)

2+ 1.5 x 10¯

4

Benzoic acid C6H5COOH + H2O → H3O+ + C6H5COO¯ 6.6 x 10¯

5

Hydrogen oxalate ion HC2O4¯ + H2O → H3O+ + C2O4

2¯ 5.4 x 10¯

5

Acetic acid HC2H3O2 + H2O → H3O+ + C2H3O2¯ 1.8 x 10¯

5

Aluminum ion Al(H2O)63+

+ H2O → H3O+ + Al(H2O)5(OH)

2+ 1.4 x 10¯

5

Carbonic acid H2CO3 + H2O → H3O+ + HCO3¯ 4.4 x 10¯

7

Hydrogen sulfide H2S + H2O → H3O+ + HS¯ 1.0 x 10¯

7

Dihydrogen phosphate ion H2PO4¯ + H2O → H3O+ + HPO4

2¯ 6.3 x 10¯

8

Hydrogen sulfite ion HSO3¯ + H2O → H3O+ + SO3

2¯ 6.2 x 10¯

8

Ammonium ion NH4+

+ H2O → H3O+ + NH3 5.7 x 10¯

10

Hydrogen carbonate ion HCO3¯ + H2O → H3O+ + CO3

2¯ 4.7 x 10¯

11

Hydrogen telluride ion HTe¯ + H2O → H3O+ + Te

2¯ 1.0 x 10¯

11

Hydrogen peroxide H2O2 + H2O → H3O+ + HO2¯ 2.4 x 10¯

12

Monohydrogen phosphate HPO42¯ + H2O → H3O

+ + PO4

3¯ 4.4 x 10¯

13

Hydrogen sulfide ion HS¯ + H2O → H3O+ + S

2¯ 1.2 x 10¯

15

Water H2O + H2O → H3O+ + OH¯ 1.8 x 10¯

16

Hydroxide ion OH¯ + H2O → H3O+ + O

2¯ < 10¯

36

Ammonia NH3 + H2O → H3O+ + NH2¯ very small

3

POLYATOMIC IONS

NAME FORMULA CHARGE

ACETATE CH3COO- -1

AMMONIUM NH4 + +1

HYDROGEN CARBONATE (BICARBONATE) HCO3 - -1

CARBONATE CO3 -2 -2

CHLORATE ClO3 - -1

CHLORITE ClO2 - -1

CHROMATE CrO4 -2 -2

DICHROMATE Cr2O7 -2 -2

DIHYDROGEN PHOSPHATE H2PO4 - -1

HYDROGEN PHOSPHATE HPO4 -2 -2

PHOSPHATE PO4 -3 -3

HYDROGEN SULFATE (BISULFATE) HSO4 - -1

SULFATE SO4 -2 -2

HYDROGEN SULFITE (BISULFITE) HSO3 - -1

SULFITE SO3 -2 -2

HYDRONIUM H3O+ +1

HYDROXIDE OH- -1

PERCHLORATE ClO4 - -1

HYPOCHLORITE ClO- (OCl-) -1

NITRATE NO3 - -1

NITRITE NO2 - -1

PERMANGANATE MnO4 - -1

THIOCYANATE SCN- -1

Patterns for Naming Polyatomic Ions

‘-ate’ ending is the general (base) form. The ending changes depending on the

number of oxygen atoms – notice the charge remains the same in these cases.

ClO3 - chlorate base oxygen atoms

ClO4 - perchlorate base + 1 oxygen atom

ClO2 - chlorite base – 1 oxygen atom

ClO- hypochlorite base – 2 oxygen atoms

4

*FOLLOW THE MOVING HYDROGEN ION*

1. Identify the acid, base, conjugate acid and conjugate base for each of the following.

a) HClO4 (aq) + H2O (l) H3O+(aq) + ClO4¯ (aq)

b) H2SO3 (aq) + H2O (l) H3O+(aq) + HSO3¯ (aq)

c) HC2H3O2 (aq) + H2O (l) H3O+ (aq) + C2H3O2¯ (aq)

d) H2S (g) + H2O (l) H3O+ (aq) + HS¯ (aq)

e) HSO3-

(aq) + H2O (l) H3O+

(aq) + SO3¯2 (aq)

f) NH3 (g) + H2O (l) NH4+ (aq) + OH¯ (aq)

g) HF (aq) + HSO3¯ (aq) F¯ (aq) + H2SO3 (aq)

h) HNO2 (aq) + HS¯ (aq) NO2¯ (aq) + H2S (aq)

2. Predict which reactant will accept a hydrogen ion and complete the products for each equation. Label each reactant as an acid or base.

List under the first reactant whether it falls under the Arrhenius (A) and/or Bronsted-Lowry (B-L) definition of an acids/bases

E.g. HBr (aq) + H2O (l) H3O+ (aq) + Br¯ (aq)

Acid Base

(A and B-L)

a) HI (aq) + H2O (l)

b) HF (aq) + H2O (l)

c) H2CO3 (g) + H2O (l)

d) CO3-2

(aq) + H2O (l)

e) O-2 (aq ) + H2O (l)

f) HSO3¯ (aq) + H2O (l)

5

Write the dissociation of each of the following in water. Predict whether each of

the following will be an electrolyte or non-electrolyte.

1. NaOH (s)

2. Na2CO3 (s)

3. Mg(OH)2 (s)

4. C6H12O6 (s)

5. HCl (g)

6. K3PO4 (s)

7. H2SO4 (aq)

8. NaC2H3O2 (s)

9. (NH4)2SO4 (s)

10. C2H5OH (l)

11. H3PO4 (aq)

12. CaCl2 (s)

6

1. In each case:

i. Complete the acid-base equation with the help of tables if needed.

ii. ii. Label the acid, base, CA, CB.

iii. Explain whether the reactants or products are favored at equilibrium.

a) H3PO4 + C2H3O2–

b) C2H3O2– + HSO4

–

c) SO32–

+ NH4+

d) HO2– + H2CO3

e) Al(H2O)63+

+ HSe–

2. List the following in decreasing (strongest to weakest) order of strength as bases.

a. CO32–

b. HCO3– c. HPO4

2– d. CH3COO

– e. HSO3

–

3. List the following substances in increasing order (weakest to strongest) of strength as acids and

bases. Some may be used more than once.

F– , H2PO4

– , HSO4

– , H2S , C2H3O2

– , HNO2 , HTe

–

7

ANSWER THE FOLLOWING QUESTIONS ABOUT Kw AND ION CONCENTRATION:

1. What is the hydroxide ion concentration in a solution with an hydronium concentration of 6.80×10–

10 mol/L?

2. What is the [H3O+] in a solution with [OH

–] of 5.67×10

–3?

3. If the [H3O+] in a nitric acid solution is 0.0020 mol/L, what is the [OH

–]?

4. If the [OH¯] in a sodium hydroxide solution is 0.050 mol/L, what is [H3O+]?

5. 0.25 moles of hydrogen chloride gas is dissolved in 2.0 L of water. Write the dissociation equation for this

gas and calculate both [H3O+] and [OH

–].

6. 10.0 g of lithium hydroxide is dissolved in 750 mL of water. Write the dissociation equation and calculate

both [H3O+] and [OH

–].

7. 10.0 g of calcium hydroxide is dissolved in 400.0 mL of solution. Write the dissociation equation and

calculate both [H3O+] and [OH

–].

8. If the [H3O+] of a barium hydroxide solution is 1.0×10

–13 mol/L, calculate the [OH

–]. How many grams

of barium hydroxide must have been used to make a Litre of this solution?

9. Calculate the [H3O+] in milk of magnesia (magnesium hydroxide) that has an [OH

–] of 1.43×10

–4 mol/L.

Answer Key

1) 1.47 x 10-5

M, 2) 1.76 x 10-12

M, 3) 5.0 x 10-12

M, 4) 2.0 x 10-13

M, 5) 0.125 M, 8.0 x 10-14

M

6) 1.79 x 10-14

M, 0.559 M 7) 1.48 x 10-14

M, 0.675 M 8) 8.6 g, 9) 6.99 x 10 -11

M

8

ANSWER THE FOLLOWING QUESTIONS ON pH and pOH:

1. Determine the pH of each of the following values

a. [H+] = 1.0 x 10

-6 b. [H

+] = 1.0 x 10

-8

c. [OH¯] = 1.0 x 10-2

d. [OH¯] = 1.0 x 10-5

e. [H+] = 2.0 x 10

-3 f. [H

+] = 3.5 x 10

-4

g. [OH¯] = 7.50 x 10-7

h. [OH¯] = 9.0 x 10-9

2. Determine the concentration of [H+] of each of the following.

a. pH = 7.00 b. pOH = 5.00

c. pH = 13.00 d. pOH = 11.00

e. pH = 3.40 f. pOH = 6.10

g. pH = 8.90 h. pOH = 13.80

3. Determine the pOH of the following if the pH is given

a. pH = 5.40 b. pH = 8.60

c. pH = 2.90 d. pH = 12.60

4. Determine the concentration of the OH¯ ions in solutions with the following pH values.

a. pH = 4.10 b. pH = 5.10

c. pH = 1.60 d. pH = 9.20

5. Calculate pH of each of the following solutions.

a. 0.0020 mol/L HCl b. 0.050 M NaOH

c. 4.0 x 10-4

M Ba(OH)2 d. 0.50 mol/L HNO3

Answers a. 6.00 b. 8.00 c. 12.0 d. 9.00 e. 2.70 f. 3.46 g. 7.88 h. 5.95

a. 1e-7 b. 1e-9 c. 1e-13 d. 1e-3 e. 4e-4 f. 1.3e-8 g. 1.3e-9 h. 0.63

a. 8.60 b. 5.40 c. 11.10 d. 1.40 a. 1.3e-10 b. 1.3e-9 c. 4e-13 d. 1.6e-5

a. 2.70 b. 12.70 c. 10.90 d. 0.30

9

pH practice

1) What is the pH and pOH of a 1.2 x 10-3

M HBr solution?

2) What is the pH and pOH of a 2.34 x 10-5

NaOH solution?

3) What is the pH and pOH of a solution made by adding water to 15 grams of hydroiodic acid until the

volume of the solution is 2500 mL?

4) What is the pH and pOH of a solution that was made by adding 400 mL of water to 350 mL of 5.0 x 10-

3 M NaOH solution?

5) What is the pH and pOH of a solution with a volume of 5.4 L that contains 15 grams of hydrochloric

acid and 25 grams of nitric acid?

6) A swimming pool has a volume of one million liters. How many grams of HCl would need to be added

to that swimming pool to bring the pH down from 7 to 4? (Assume the volume of the HCl is negligible)

ANSWER KEY

1. pH: 2.9 pOH: 11.1 2. pOH: 4.6 pH: 9.4 3. pH: 1.3 pOH: 12.7

4. pOH: 2.7 pH: 11.3 5. pH: 0.82 pOH: 13.18 6. 3545 g

10

ANSWER THE FOLLOWING DISSOCIATION QUESTIONS:

1. Calculate the concentration of all species in a 0.70 mol/L HNO3 solution.

2. Determine the [H3O+] in 0.90 mol/L solution of weak acid H2S. (Ka = 1.0 x 10

-7) (3.0x 10

-4 M)

3. Find the concentration of all species in a 0.10 M solution of NaOH.

4. Determine the concentration of all species in a 0.65 mol/L solution of an ammonia, if the

base dissociation constant is 1.8 x 10-5

. (3.4 x 10-3

M)

5. Find the [H+] in a 0.86 M solution of the weak acid H2O2. (Ka = 2.4 x 10

-12) (1.4 x 10

-6 M)

6. If [H3O+] = 4.5 x 10

-6 mol/L in a 0.45 mol/L solution of the weak acid HX, calculate

percent dissociation. (0.001%)

7. Find the percent dissociation in 0.87 M solution of the weak base HPO42¯

if Kb

is 1.6 x 10-7

. (0.043%)

11

8. Calculate the [H+] of a 0.38 mol/L weak acid that is dissociated 0.12%. (4.56 x 10

-4 M)

9. Determine the Ka for an acid, HA, if a 0.45 M solution is dissociated 0.025%. (2.8 x 10-8

)

10. Calculate the the percent dissociation of a 0.60 mol/L aniline (C6H5NH2) solution (Kb = 3.8×10–10

) if

it dissociates according to the following equation: (0.0025%)

C6H5NH2 + H2O C6H5NH3+ + OH

–

11. Determine the Ka for an acid HA if a 0.750 mol/L solution is dissociated 0.015%. (1.7 x 10-8

)

12. If [H3O+] = 4.5 ×10

–10 mol/L, calculate the Ka for a weak acid in a solution of 0.80 mol/L of an acid HB.

(2.5 x 10-19

)

13. Calculate the pH of a 0.10 mol/L solution of hypochlorous acid, HOCl (Ka = 3.5 ×10–8

) (4.2)

12

14. A 0.20 mol/L solution of the weak base HPO42–

has a pH of 9.00. Find the Kb. (5.0 x 10-10

)

15. Calculate the Ka of a weak acid, HX, if a 0.25 mol/L solution has a pH of 4.40. (6.3 x 10-9

)

16. At 25°C, a 0.010 mol/L ammonia solution is 4.3% ionized. Calculate the pOH and pH. (3.4, 10.6)

17. Hydrazine (N2H4) is a weak base with a Kb of 3.0×10–6

. The reaction of hydrazine in water

is H2NNH2 + H2O H2NNH3+ + OH

–

Calculate the the pH of a 2.0 mol/L solution of hydrazine. (11)

18. Calculate the percent dissociation of a 0.20 mol/L solution of the weak acid, HNO2, if the pH of

the solution is 4.20. (0.032%)

13

ANSWER THE FOLLOWING DISSOCIATION QUESTIONS:

1. Calculate the original concentration of the weak base, C2H3O2¯ (acetate ion), if [OH¯] = 1.5 x 10

-5

and Kb = 5.6 x 10-10

. (0.4 M)

2. Calculate percent dissociation of a 0.60 M aniline (C6H5NH2) solution (Kb = 3.8 x 10-10

) if it

dissociates according to the following equation: (0.0025%)

C6H5NH2 + H2O C6H5NH3+ + OH¯

3. Determine the Ka for an acid HA if a 0.750 M solution is dissociated 0.015%. (1.7 x 10-8

)

4. Compute the concentration of [OH¯] in a 0.75 mol/L solution of Mg(OH)2.

5. If [H3O+] = 4.5 x 10

-10 mol/L, calculate Ka in a solution of 0.80 mol/L of an acid HB. (2.5 x 10

-19)

6. Determine the concentration of all species plus the percent dissociation in a 0.60 mol/L

ammonia solution. (Kb = 1.8 x 10-5

) (3.3 x 10-3

M, 3.3 x 10-3

M, 0.6 M, 0.55%)

7. Calculate the concentration of a solution of acetic acid (Ka = 1.8 x 10-5

) with pH = 3.00.

(0.056)

14

Are each of the following salts acidic, basic or neutral in water? Explain why.

1. Sodium sulfate

2. Potassium phosphate

3. Sodium nitrate

4. Sodium sulfide

5. Potassium chloride

6. Magnesium nitrate

7. Iron (III) Nitrate

8. Sodium carbonate

9. Potassium oxalate

10. Ammonium iodide

11. Potassium acetate

12. Chromium (III) bromide

13. Potassium dihydrogen phosphate

14. Sodium nitrite

15. Calcium oxide

15

ANSWER THE FOLLOWING NEUTRALIZATION QUESTIONS:

1. Write the complete reaction that occurs when the following acid and bases are reacted. a) Hydrochloric acid and sodium hydroxide.

b) Sulfuric acid and potassium hydroxide.

c) Nitric acid and calcium hydroxide.

d) Phosphoric acid and lithium hydroxide.

e) Sulfuric acid and aluminum hydroxide. 2. Calculate the concentration of a solution of KOH if 140.0 mL of the base is needed to neutralize 22.5

mL of 0.175 mol/L acid HNO3.

3. Determine the volume of 0.750 mol/L LiOH required to neutralize 56.0 mL of 0.350 mol/L H2SO4.

4. What volume of 0.240 mol/L H2SO4 can be neutralized by 50.0 mL of 0.360 M NaOH?

5. Calculate the concentration of the acid, if 25.0 mL of H3PO4 is required to neutralize 19.0 mL of

0.830 mol/L KOH. 6. What volume of 0.100 mol/L HCl is required to just neutralize 10.0 g of solid NaOH?

7. What volume of 0.250 mol/L nitric acid is needed to just neutralize 25.0 g of magnesium hydroxide?

8. What mass of calcium hydroxide is needed to just neutralize 250.0 mL of 0.100 mol/L HCl? Assume

the volume does not change.

2. 0.0281 mol/L 3. 52.3 mL 4. 37.5 mL 5. 0.210 mol/L 6. 2.50 L 7. 3.43 L 8. 0.926 g

16

Titrations Worksheet

1. I titrated 3.5 mL of NaOH with 25 mL of 5.0 x 10-2

M HCl. Find the concentration of this base

and determine its pH. (0.36 M, 13.6)

2. If it took me 25.4 mL of 5.0 mM HCl to titrate 50.0 mL of a strong basic solution with unknown

concentration, what were the concentration and pH of the basic solution? (2.54 x 10-3

M, 11.4)

3. How many mL of 0.010 M NaOH will be required to neutralize 10.0 mL of HCl with a pH of 1.0? (100 mL)

17

ANSWER THE FOLLOWING QUESTIONS ON TITRATIONS:

1. A sample of vinegar is titrated with a 0.990 mol/L sodium hydroxide solution, to determine

the concentration of acetic acid. Given the following data, a. Calculate the concentration of acetic acid in the vinegar for each trial.

b. Calculate the average concentration over the three trials. (0.830 mol/L)

2. The neutralization of 0.900 g of an unknown monoprotic solid acid required 30.00 mL of 0.150

mol/L NaOH. Calculate the molar mass of the acid. (200 g/mol)

3. A sample of a monoprotic acid (molar mass 97.09 g/mol) is dissolved in enough water to make 250.0 mL of

solution. A 12.00 mL aliquot of the acid solution is titrated with a 0.0850 mol/L solution of NaOH. If 17.55

mL is required to reach the endpoint, what is the mass of the original sample? (3.02 g)

18

4. Aspirin™ tablets are made of acetylsalicylic acid (ASA) and fillers. An Aspirin™ tablet with mass of

0.500 g was powdered, suspended in water and titrated with 0.150 mol/L NaOH solution. If it requires 11.80 mL of NaOH solution to reach the endpoint, how much ASA does the tablet contain? ASA is a

monoprotic acid with a formula of C9H8O4. (0.319 g)

5. A student pipetted 25.0 mL of an aqueous solution of an unknown monoprotic acid into an Erlenmeyer flask,

added about 25 mL of water and titrated with a standard 0.0985 mol/L sodium hydroxide solution. The pH

was measured after each addition. The graph below shows the graph obtained.

Use the graph to answer the following questions.

a. What was the concentration of the unknown acid? (0.104 mol/L)

b. What would be a suitable range for an indicator to change colour for this titration?

19

Acids and Bases Review

1. Explain how the Lewis definition of a base is different from that of the Arrhenius definition of a base. Are

Arrhenius bases also bases under the Lewis definition? Explain.

2. Determine the type of reaction occurring below. If possible label the conjugate acid-base pair in the

appropriate place (Think about what is taking place in the reaction).

a. H2SO4 + H2O HSO3-1

+ H3O

b. Ca(OH)2 + 2 HNO3 Ca(NO3)2 + 2 H2O

c. NaCl Na+ + Cl

-

3. What’s the pH of a 3.3 x 10-5

M NaOH solution?

4. Find the pH of a 0.0050 M acetic acid solution. Ka = 1.8 x 10-5

(3.5)

5. What is the pH of a solution that contains 2.4 x 10-5

moles of hydrobromic acid in 0.50 L of water? (4.3)

20

6. What is the pH of a solution that contains 25 moles of nitric acid dissolved in 5000 L of water? (2.30) 7. In a few steps, describe how you would titrate a base of unknown concentration with an acid with

concentration of 1 M.

8. I did a titration where it took 50 mL of 0.1 M hydrochloric acid to neutralize 500 mL of a base with

unknown concentration. Using this information, what was the concentration of the base? (0.01 M)

9. I did a titration where it took 25 mL of 5 M NaOH to neutralize 1000 mL of an acid with

unknown concentration. Using this information, what was the concentration of acid? (0.125 M)

10. If it takes 560 mL of 0.0050 M NaOH to neutralize 100.0 mL of H2SO4 solution with

unknown concentration, what was the original pH of the H2SO4 solution? ( 1.9)

21