Thermo
dynamics and Solubility
dynamics and Solubility
What is the solubility product expression for Fe(OH)2(s) in equilibrium with its ions in a saturated aqueous solution?
Dissolution: Fe(OH)₂(s) ⇌ Fe²⁺(aq) + 2 OH⁻(aq)
Ksp=[Fe2+][OH−]2
What is the conjugate base of HNO2?
NO2-
What is the pH of orange juice in which the hydronium ion concentration is 8.3 x 10-5 M?
4.1
Which of the following salts forms aqueous solutions with pH = 7?
a. SrF2
b. Sr(CHO2)2
c. Sr(CN)2
d. SrCO3
e. Sr(NO3)2
e. Sr(NO3)2
Use the given Ka and Kb values to rank the following solutions in order of increasing pH: 0.1 M C5H5NHBr, 0.1 M BaCl2, 0.1 M KCN, 0.1 M NaNO2
Nitrous acid (HNO2) Ka= 4.5 x 10-4
Hydrocyanic acid (HCN) Ka= 4.9 x10-10
Pyridine (C5H5N) Kb= 1.7 x 10-9
Methylamine (CH3NH2) Kb= 4.4 x 10-4
C5H5NHBr < BaCl2 < NaNO2 < KCN
The solubility of Ni(OH)2 in water at 25 C is 4.9 x 10-4 g/L. What is its Ksp value?
1. Convert to molar solubility s: MNi(OH)2 ≈ 92.7 g mol−1
s=4.9 × 10−4 / 92.7 ≈ 5.3×10−6 mol L−1
2. Ni(OH)₂(s) ⇌ Ni²⁺ + 2OH⁻
[Ni2+]=s, [OH−]=2s
Ksp=[Ni2+][OH−]2= s(2s)2 = 4s3
Ksp≈4(5.3×10−6)3≈5.9×10−16
Which of the following is a strong acid?
a. phosphoric acid H3PO4
b. carbonic acid H2CO3
c. perchloric acid HClO4
d. nitrous acid HNO2
e. acetic acid CH3COOH
c. Perchloric acid, HClO4
What is the pH of a 4.2 x 10-3 M solution of LiOH?
11.6
Which of the following statements is not true about a solution that is initially 0.36 M in hydrocyanic acid (HCN) and 0.40 M in sodium cyanide (NaCN)?
a. The presence of the cyanide ion will inhibit the dissociation of HCN.
b. [HCN]eq = 0.36 -x, [CN-]eq = 0.40 +x, [H3O+] = x
c. The conjugate base of HCN is the cyanide ion, CN-
d. The pH of this solution is lower than the pH of a 0.36 M HCN solution
e. The pH of this solution is higher than the pH of a 0.36 M HCN solution
d. The pH of this solution is lower than the pH of a 0.36 M HCN solution
An aqueous solution at 25 C has a H3O+ concentration of 5.9 x 10-10. Calculate the OH- concentration.
1.7 x 10-5
A reaction has ΔH = +45 kJ and ΔS = +125 J/K.
At 298 K, is the reaction spontaneous?
Use: ΔG=ΔH−TΔS
Convert ΔS: 125 J/K = 0.125 kJ/K
ΔG = 45 -(298)(0.125) = +7.75 kJ
ΔG > 0 → Not spontaneous at 298 K
How can I describe the pH of a basic solution?
pH > 7
What volume of concentrated 8.0 M hydrochloric acid (HCl) is required to produce a 250 mL hydrochloric acid solution with pH = 1.2?
2.0 mL
4.45
Given that hydrocyanic acid (HCN) has an acid dissociation constant, Ka= 6.17 x 10-10, what is pKa for hydrocyanic acid?
9.21
A reaction has ΔH < 0 and ΔS < 0.
At what temperatures will the reaction be spontaneous?
(a) All temperatures
(b) Low temperatures
(c) High temperatures
(d) Never
(b) Low temperatures
(When both ΔH and ΔS are negative, spontaneity only occurs at low T.)
The stronger the acid, the ____________.
a. stronger its conjugate base
b. weaker its conjugate base
c. more concentrated the acid
d. less concentrated the conjugate base
e. more concentrated the conjugate base
b. weaker its conjugate base
What mass of solid potassium hydroxide (KOH) is required to make a 500.0 mL potassium hydroxide solution with pH = 13.80 ?
17.7 g
Which of the following can be mixed together in water to produce a buffer solution?
a. HNO2 and NaNO2
b. HClO4 and NaClO4
c. HNO3 and NaNO3
d. H2SO4 and NaHSO4
e. HBr and NaBr
a. HNO2 and NaNO2
What is the correct expression for the base protonation constant, Kb, for the reaction of dimethylamine (C5H13N), a weak base, with water?
Kb= [C5H13NH+][OH-] / [C5H13N]
Which sample has the largest number of microstates (W) and therefore the highest entropy?
(a) 1 mol CO₂(s)
(b) 1 mol CO₂(l)
(c) 1 mol CO₂(g)
(d) 1 mol CO₂(g) at 2 atm
(e) 1 mol CO₂(g) at 0.5 atm
Correct Answer: (e) CO₂(g) at 0.5 atm
(Lowest pressure → largest volume → greatest number of accessible microstates → highest entropy.)
9.3
The acid dissociation constant, Ka, of boric acid (H3BO3) is 5.8 x 10-10. What is the pH of a 1.2 M solution of boric acid?
4.6
A chemistry student is given 125.0 mL of a 1.60 M hydrocyanic acid (HCN) solution. HCN is a weak acid with Ka= 4.9 x 10-10. What mass of NaCN (MM=49.01 g/mol) should the student dissolve in the HCN solution to turn it into a buffer with pH = 9.18?
7.3 g
9.8