Question

UTILIT In this solution is a. 2.6 x 10-1° M b. 3.8 x 10 M c. 9.58 d. 4.42 e. none of these 21. How many moles of pure NaOH must be used to prepare 1.0 L of a solution that has pH = 12.26? a. 8.2 x 10-16 mol b. 0.018 mol c. 5.5 x 10-13 mol d. 1.74 mol e. none of these 22. Calculate the pH of a 0.045 M HCl solution. K a. 1.23 b. 1.35 c. 12.65 d. 12.29 e. none of these 23. Which statement is true for a strong base solution with a concentration greater than 1.0 M? a. POH > pH b. pH > POH C. pH <0 d. pH<14 e. Two of these (a-d) are true. 24. A solution is prepared by dissolving 111.9 g HCl(g) in enough water to make 160.0 L of solution. The pH of this solution is a. 1.72 b.12.28 c. 0.155 d. 3.07 e. none of these

explain 21,22,23

Answer 1

21)

use:

pH = -log [H+]

12.26 = -log [H+]

[H+] = 5.495*10^-13 M

use:

[OH-] = Kw/[H+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

[OH-] = (1.0*10^-14)/[H+]

[OH-] = (1.0*10^-14)/(5.495*10^-13)

[OH-] = 1.82*10^-2 M

SO,

Mol of NaOH = [NaOH] * volume in L

= 1.82*10^-2 M * 1 L

= 1.82*10^-2 mol

Answer: 1.82*10^-2 mol

22)

Given:

[H+] = 0.045 M

use:

pH = -log [H+]

= -log (4.5*10^-2)

= 1.35

Answer: 1.35

23)

[OH-] > 1.0

POH = -log [OH-]

pOH will be less than 0

So,

pH will be greater than 14 since pH + pOH = 14

B is correct

C is correct

Answer: e