The hydronium-ion concentration of a 0.050 M solution of a weak acid is 4.3 × 10

Question

The hydronium-ion concentration of a 0.050 M solution of a weak acid is 4.3 × 10-3 M. The acid-dissociation constant is 1.37 × 10-4 at 25oC. What is the pH of this solution?
A) 2.37 B) 3.86 C) 5.45. D) 0.066 E) 1.30

Which of the following solutions is basic?
A) [OH-]=1.0x10-7 M D) [H3O+]>1.0x10-7 M

B) [H3O+]=1.0x10-10 M E) [OH-]<1.0x10-10 M

C) [OH-] = 1.0 x 10-10 M

What is the pH of a 0.32 M solution of methylamine (CH3NH2, Kb = 4.4x10–4) at 25oC?

A) 1.93 B) 12.07 C) 13.51 D) 5.57 E) 0.49

The rate constants for the first-order decomposition of a compound are 5.72 × 10–4 s-1 at 36°C and 1.83 × 10–3 s-1 at 62°C. What is the value of the activation energy for this reaction? (R = 8.31 J/(mol · K))

A) 0.830 kJ/mol D) 16.7 kJ/mol

B) 0.372 kJ/mol E) 38.5 kJ/mol

C) 0.360 kJ/mol

The solubility of CaSO4 in pure water at 0oC is 1.19 g/L. What is the value of the solubility product?

A) 7.65×10-5 B) 8.74×10-3 C) 1.19×10-3 D) 9.35×10-2

What is the boiling-point change for a solution containing 0.284 mol of naphthalene (a nonvolatile, nonionizing compound) in 250. g of liquid benzene? (Kb = 2.53°C/m for benzene)

A) 2.23°C B) 0.180°C C) 2.87°C D) 8.91°C E) 0.719°C

The equilibrium expression for the hydrolysis of a weak base, A–, in water is:

A) Kb = [OH–][HA]/[A–] D) Kb = [OH–][H3O+]/[A–]

B) Kb = [OH–][HA]/[A–][H3O+] E) Kb = [A–]/[OH–][H3O+]

C) Kb = [OH–][A–]/[HA]

What is the percent ionization of a 2.0 M HC2H3O2 solution (Ka = 1.8x10-5) at 25°C?

A) 0.18% B) 1.6% C) 0.60% D) 0.30% E) 0.21%

If 10.8 g of naphthalene, C10H8, is dissolved in 119.6 g of chloroform, CHCl3, what is the molality of the solution?
A) 10.8m B) 0.0844m C) 0.0842m D) 0.0828m E) 0.705m

A rate constant for a particular reaction is 0.0090 s–1. What is the overall order of this reaction?

A) 2 B) 4 C) 3 D) 1 E) 0

Arrange the following aqueous solutions in order of increasing boiling points: 0.300m C6H12O6, 0.110m K2CO3, and 0.050m Al(ClO4)3

A) C6H12O6 < Al(ClO4)3 < K2CO3 D) Al(ClO4)3 < C6H12O6 < K2CO3 B) K2CO3 < Al(ClO4)3 < C6H12O6 E) C6H12O6 < K2CO3 < Al(ClO4)3 C) K2CO3 < C6H12O6 < Al(ClO4)3

Explanation / Answer

The hydronium-ion concentration of a 0.050 M solution of a weak acid is 4.3 × 10-3 M. The acid-dissociation constant is 1.37 × 10-4 at 25oC. What is the pH of this solution?
A) 2.37 B) 3.86 C) 5.45. D) 0.066 E) 1.30

in equilibrium

HA <-> H+ + A-

then

[H+] = 4.3*10^-3

[A-] =[H+] =  4.3*10^-3 (due to stoichiometry)

[HA] = 0.05-4.3*10^-3 = 0.0457

Ka = [H+][A-]/[HA] = (4.3*10^-3)(4.3*10^-3)/0.0457)

Ka = 0.00040459518

Ka = 4.04*10^-4

pH = -log(H+) = -log(4.3*10^-3) = 2.3665

pH = 2.3665

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