Question

1.49 M 0.054M 18.42M Question 18 1 pts What will be the weight of KOH (in grams/liter) required to make a solution of pH 10? (First determine the OH concetration needed and then the amount of KOH to add) 0.0056 g/L O 0.112 g/L 0.056 g/L 0.56 g/L Question 19 1 pts What is the concentration of [OH-] in a solution whose pH 3 is

Answer 1

18)
Given:
pH = 10

use:
pH = -log [H+]
10 = -log [H+]
[H+] = 1*10^-10 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)/(1*10^-10)
[OH-] = 1*10^-4 M

So,
[KOH] = 1*10^-4 M

Consider 1 L of solution

volume , V = 1 L


use:
number of mol,
n = Molarity * Volume
= 1*10^-4*1
= 1*10^-4 mol

Molar mass of KOH,
MM = 1*MM(K) + 1*MM(O) + 1*MM(H)
= 1*39.1 + 1*16.0 + 1*1.008
= 56.108 g/mol

use:
mass of KOH,
m = number of mol * molar mass
= 1*10^-4 mol * 56.11 g/mol
= 5.611*10^-3 g
Answer: option 1