CHEM 1412 Practice Problems

Chapters 16, 17, & 19

1.Define the following:

a) Bronsted acidb) Bronsted base

c) Lewis acidd) Lewis base

e) strong acidf) strong base

g) weak acidh) weak base

i) autoionization of waterj) ion-product constant for water

k) hydronium ionl) conjugate acid, base, & pair

m) common ion effectn) end point

2.Complete the following table:

Compound / Conjugate Base / Conjugate Acid
H2O
----- / HI
NH4+
HSO4-
S2-
CH4 / -----
HNO3
OH-

3.Calculate the hydrogen ion concentration in the following solutions:

a) a rainwater sample with a pH of 6.3

b) an ammonia solution with a pH of 13.4

c) a solution of NaOH with pOH = 1.5

4.Calculate the pH of the following solutions:

a) a 0.0250 M solution of HBr

b) a 15.0 M solution of KOH

c) a 0.0175 M solution of Ca(OH)2

d) 50.0 mL of 0.150 M HNO3 mixed with 200 mL of 0.0750 M NaOH

e) 2.50 g of solid Ca(OH)2 added to 75.0 mL of 3.00 M HCl

5.Will aqueous solutions of the following compounds be acidic, basic, or neutral?

a) KNO3b) Ba(OH)2c) NaC2H3O2

d) NaCle) NaFf) ZnCl2

g) NH3h) NH4Bri) KNO2

6.Write a) the net ionic chemical equation for either the weak acid dissociation or the weak

base hydrolysis, and b) the equilibrium constant expression, for the following aqueous

solutions:

a) HF (aq)b) NaF (aq)c) NH3 (aq)

d) NH4Cl (aq)e) NaC7H5O2 (aq)e) Fe(NO3)3 (aq)

7.What is the pH of a 0.100 M solution of the weak acid phenol, C6H5OH? Ka for phenol is

1.3 X 10-10.

8.What is the pH of a 0.250 M solution of sodium butanoate, NaC4H7O2? Ka for butanoic

acid is 1.5 X 10-5.

9.Did you know that hydrogen peroxide, H2O2, is a very weak acid (Ka = 2.4 X 10-12)? The

labelon a bottle ofhousehold peroxide reads,"ACTIVE INGREDIENT: HYDROGEN

PEROXIDE 3%,INERT INGREDIENTS 97%". What is the pH of this solution? The

density of the solution will be very close to that of pure water.

10.Calculate the pH of a solution prepared by mixing 100 mL of 0.250 M acetic acid with 400

mL of 0.05 M NaOH. Ka for acetic acid = 1.8 X 10-5.

11.A solution of 0.15 M in NH3 and 0.25 M inammonium chloride, NH4Cl. What is the pH of

the solution? Ka for ammonium ion is 5.6 X 10-10.

12.Strong acids are 100% dissociated in aqueous solution. What is the percent dissociation of

a 0.01 M solution of a weak acid such as acetic acid in water? Compare this value to the

percent dissociation ofa 1.0 Msolution. Would you expect the percent dissociation to

change with concentration? Ka for acetic acid = 1.8 X 10-5.

13.What is the pH of a 1.0 X 10-9 M solution of a strong acid like HCl? Does taking the log of

the H+ ion concentration give an answer that makes any sense? Explain.

14.Calculate the molar solubility of iron(III) hydroxide, Fe(OH)3, in water.

Ksp for Fe(OH)3= 4.0X 10-38.

15.a) What is the molar solubility of calcium hydroxide, Ca(OH)2? What is the pH of this

solution? b) What is the molar solubility of Ca(OH)2 if the pH of the solution is adjusted

to a value of 13 at equilibrium? Ksp for Ca(OH)2 = 5.5 X 10-6.

16.100 mL of 0.020 M BaCl2 is mixed with 100 mL of 0.010 M NaF. Will a precipitate of

BaF2 form? Ksp for BaF2 = 1.0 X 10-6.

17.An unknown solution of H3PO4 was titrated with 0.100 M NaOH. If 50.0 mL of the acid

solution required 27.5 mL of the NaOH solution to reach the end point, what is the

molarity ofthe H3PO4 solution?

18.Define the following:

a) entropyb) enthalpy

c) free energyd) the first, second, and third laws of thermodynamics

19.Which of the following will have the higher molar entropy?

a) H2O (l) or H2O (s)

b) N2 (g) at 1 atm pressure or N2(g) at 0.1 atm pressure

c) Fe (s) at 25oC or Fe (s) at 100oC

d) ice at a temperature of 0oC or ice at a temperature of -50 oC

20.Is S positive or negative for the following reactions?

a) N2(g) + 3H2 (g)  2NH3 (g)

b) 2Mg (s) + O2 (g)  2MgO (s)

c) CO2 (g) + H2O (l)  H2CO3 (aq)

d) 2CuO (s)  2Cu (s) + O2 (g)

21.Given the following entropies:

So for SO2 (g) = 0.249 kJ/mole K

So for O2 (g) = 0.205 kJ/mole K

So for SO3 (g) = 0.256 kJ/mole K,

Calculate So for the reaction 2SO2 (g) + O2 (g)  2SO3 (g)

22.From the following standard enthalpies of formation and entropies:

KClO3 (s)Hof= -391.2 kJ/moleSo = 0.143 kJ/mole K

KCl (s)Hof= -435.9 kJ/moleSo = 0.0827 kJ/mole K

O2 (g)Hof= 0So = 0.205 kJ/mole K

Calculate Gofor the reaction 2KClO3 (s)  2KCl (s) + 3O2 (g)

23.Knowing that Ka for acetic acid = 1.8 X 10-5, calculate Gofor the dissociation of this

substance in aqueous solution at 25oC.

24.Given that Go= -33.32 kJ for the reaction N2 (g) + 3H2 (g)  2NH3 (g), calculate G

for the reaction if we start with N2 gas at an initial pressure of 2.0 atm, H2 gas at

pressure of 2.0 atm, and NH3 (g) at an initial pressure of 1.0 atm.

25.Given Goffor H2O (l) = -236.81 kJ/mole, calculate the equilibrium constant Keq for the

reaction 2H2O (l)  2H2 (g) + O2 (g) at 25oC.

26.Given that Go= -213.9 kJ for the reaction

Cu2S (s) + O2 (g)  2 Cu (s) + SO2(g)

and Go= -300.1 kJ for the reaction

S (s) + O2 (g)  SO2 (g)

Calculate Gofor the reaction

Cu2S (s)  2Cu (s) + S (s)