Please help. And for #8 please explain why. Farmers who raise cotton once used a
ID: 966475 • Letter: P
Question
Please help. And for #8 please explain why.
Farmers who raise cotton once used arsenic acid, H_3ASO_4, as a defoliant at harvest time. Arsenic acid is a polyprotic acid with K_a1 = 2.5 times 10^-4, K_a2 = 5.6 times 10^-8, and K_a3 = 3 times 10^-13. What is the pH of a 0.500 M solution of arsenic acid? SmallCircle 0.85 SmallCircle 1.95 SmallCircle 3.90 SmallCircle 4.51 SmallCircle 3.14 What is the value of K_b for the cyanide anion, CN ? k_a(HCN) = 6 times 10^-10 SmallCircle5 times 10^-3 SmallCircle 2 times 10^-5 SmallCircle.4 times 10^-5 SmallCircle.4times10^-10 SmallCircle.4 times 10^-24 A solution is prepared by adding 0.10 mol of sodium sulfide, Na2S, to 1.00 L of water. Which statement about the solution is correct? The solution is basic. The solution is neutral. The solution is acidic. The concentration of sodium ions and sulfide ions will be identical. The concentration of sulfide ions will be greater than the concentration of sodium ions.Explanation / Answer
6. pH of 0.5 M H3AsO4
Ka1 = [H+][H2AsO4-]/[H3AsO4]
2.5 x 10^-4 = x^2/0.5
x = [H+] = 0.011 M
pH = -log[H+] = 1.95
So the answer is,
(B) 1.95
7. Kb for CN-,
Kb = Kw/Ka = 1 x 10^-14/6 x 10^-10 = 2 x 10^-5
So the answer is,
(B) 2 x 10^-5
8. Dissolved 0.1 mol of Na2S in 1 L water
molarity of solution = 0.1/1 = 0.1 M
S^2- + H2O <==> HS- + OH-
So the solution has excess OH- in it, which makes the solution basic.
A. The solution is basic