The concentration of H_3O^+ in a solution is 3 times 10^-4 M at 25 degree C. Wha

Question

The concentration of H_3O^+ in a solution is 3 times 10^-4 M at 25 degree C. What is its hydroxide-ion concentration? A) 3 times 10^-10 M B) 5 times 10^-10 M C) 6 times 10^-10 M D) 3 times 10^-11 M E) 3 times 10^-4 M A 1.0 M solution of a weak monoprotic acid is 0.40% ionized. What is the acid-ionization constant, K_a, of the weak acid? A) 1.6 times 10^-7 B) 4.0 times 10^-1 C) 4.0 times 10^-3 D)1.6 times 10^-5 E)1.6 times 10^-6 If 500 mL of 1.1 times 10^-6 M AgNO_3 is mixed with 500 mL of 1.1 times 10^-6 M NaBr, what will occur? For AgBr, K_sp = 5 times 10^-13. A) Sodium bromide will precipitate. B) Silver(I) bromide will precipitate. C) The concentration of Ag^+ will be 1.1 times 10^-6 M. D) No precipitation will occur. E) 5.5 times 10^-7 mol of AgBr will form.

Explanation / Answer

4)

[H3O+] = 3*10^-4 M

use:

[OH-] = 10^-14 / [H3O+]

= 10^-14 / (3*10^-4)

= 3*10^-11 M

Answer: D

5)

Let the acid be HA

HA        <—> H+   +   A-

1.0            0           0   (initial)

1.0-x          x           x   (at equilibrium)

% ionized = x*100/c

0.40 = x*100/1.0

x = 0.004 M

Ka = x*x / (1.0-x)

Ka = (0.004 *0.004)/(1.0-0.004)

   = 1.6810^-5

Answer: D

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