Question

1) The pOH of a solution is related to pH using the formula pOH = 14.00 − pH.

If a solution has a pH of 7.74, what is the pOH at 25^oC?

2) If an aqueous solution at 25^oC has a hydroxide concentration equal to 0.000047M, what is the concentration of hydronium ion in the solution?

Report your answer in scienftic notation.

3) What is the pH of a 0.033M HNO₃ solution?

4) What is the pH of a 0.046M KOH solution?

5) What is the pH of a 0.047M Mg(OH)₂ solution?

HINT: What is the total concentration of hydroxide if 1 mol of magnium hydroxide yields 2 moles of hydroxide?

Answer 1

1)

we know that

pOH = 14 - pH

so

pOH = 14 - 7.74

pOH = 6.26

so

pOH is 6.26

2)

we know that

[H30+] [OH-] = 10-14

given

[OH-] = 0.000047

so

[H30+] [0.000047] = 10-14

[H30+] =2.128 x 10-10

3)

HN03 ---> H+ + N03-

[H+] = [HN03-] = 0.033

so

pH = -log [H+]

pH = -log 0.033

pH = 1.48

4)

KOH ---> K+ + OH-

[OH-] = [KOH]

so

[OH-] = 0.046

pOH = -log [OH-]

pOH = -log 0.046

pOH = 1.34

pH = 14 - pOH

pH = 14 - 1.34

pH = 12.66

5)

Mg(OH)2 ---> Mg+2 + 2OH-

so

[OH-] = 2 x 0.047 = 0.094

pOH = -0.094 = 1.027

so

pH = 14 - pOH

pH = 14 - 1.027

pH = 12.973