Determine the pH of a KOH solution made by mixing 0.251 g KOH (s) with enough wa

Question

Determine the pH of a KOH solution made by mixing 0.251 g KOH (s) with enough water to make 1.00 times 10^2 mL of solution. Assume 100% purity for the KOH (s). A. 1.35 B. 2.35 C.7.00 D. 11.65 E. 12.65 Predict the direction in which the equilibrium will lie for the following reaction: H_3PO_4(aq) + HSO_4 (aq) H_2PO_4 (aq) + H_2SO_4(aq). K_a1(H_3PO_4) = 7.5 times 10^3; K_a(H_2SO_4) = very large A. to the right B. to the left C. in the middle For H_3PO_4, K_a2 = 7.3 times 10^6, K_a3 = 62 times 10^6, and K_a3 = 4.8 times 10^13. An aqueous solution of Na_3PO_4 therefore would be A. neutral B. basic C. acidic Calculate the pH of a solution of 0.10 M HA (aq). The acid H_2A has K_a1 = 6.5 times 10^2 and K_a2 = 6.1 times 10^-5. A. 1.19 B.2.70 C.4.21 D.5.40 E. 8.61 Calculate the pH of a solution of 0.10 M A^2 (aq). The acid H_2A has K_a1 = 6.5 times 10^2 and K_a_2 = 6.1 times 10^-5 A. 1.19 B.2.70 C.421 D.5.40 E. 8.61 A solution is formulated that contains 3 times 10^-8 M KOH at 50 degree C (K_w = 8.0 timesw 10^14). The pH of this solution is expected to be: A. Exactly 6.55 B. Exactly 6.00 C. Exactly 7.00 D. In the range 7.00-7.10 E. In the range 655 - 6.65 A solution is prepared that contains 0.10 M KOH (aq) at 25 degree C. Considering activity coefficients, the pH of this solution will be: A. Exactly 13.00 B. Slightly higher than 13.00 C. Slightly lower than 13.00 D. There is no way to ascertain the pH of this solution using activity coefficients.

Explanation / Answer

6)
mass of KOH = 0.251 g
molar mass of KOH = 56.1 g/mol

number of moles of KOH = mass/molar mass
=0.251/56.1
=4.474*10^-3 mol

volume = 1.00*10^2 mL = 0.100 L

[KOH] = number of mol / volume
= (4.474*10^-3)/(0.100)
=0.04474 M

so,
[OH-] = 0.04474 M

[H+] = 10^-14 /[OH-]
=10^-14/(0.04474 )
= 2.235*10^-13 M

pH = -log [H+]
= -log (2.235*10^-13)
=12.65

Answer: E

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