Question

What is the pH of a 8.6 x 10^-8 M solution of HCl(aq) at 25 °C? 

Report your answer to the hundredths place. 

Assuming complete dissociation, what is the pH of a 3.98 mg/L Ba(OH)₂ solution?

Arrange the aqueous solutions from the most acidic to the most basic, at 25 °C. 

Each value represents a different aqueous solution at 25°C. Acidic Basic each solution as acidic, basic, or neutral. 

Answer 1

1) The pH is calculated:

pH = - log [HCl] = - log 8.6x10 ^ -8 = 7.07

2) The OH- molar concentration is calculated:

[OH-] = 3.98 mg / L * (1 g / 1000 mg) * (1 mol Ba (OH) 2 / 171.34 g) * (2 mol OH- / 1 mol Ba (OH) 2) = 4.6x10 ^ - 5M

The pOH and the pH are calculated:

pOH = - log 4.6x10 ^ -5 = 4.34

pH = 14 - 4.34 = 9.66

3) Substances are ordered:

i) [H3O +] = 1x10 ^ -3 M

ii) [OH-] = 1x10 ^ -9 M

iii) pH = 7

iv) pH = 10

4) Substances are classified:

Acids: [H +] = 3.1x10 ^ -3

pOH = 11.21

pH = 3.14

[OH-] = 3.6x10 ^ -10

Neutral: pH = 7

[H +] = 1x10 ^ -7

Basic: pH = 8.96

pOH = 4.79

[H +] = 7.5x10 ^ -12

[OH-] = 7x10 ^ -2