Question

HELP ASAP PLEASE!!

1) Determine the hydronium and hydroxide ion concentrations in a solution that is 2.0 × 10-2 M NaOH
2) Determine the pH of a solution that is 5.0 × 10-4 M HNO3+
3) Determine the pH of a 3.45 × 10-2 M Sr(OH)2 solution.
4) The pH of a solution is determined to be 7.0. What is the hydronium ion concentration of this solution?
5) The pH of an aqueous solution is measured as 5.00 Calculate the [H3O+] and the [OH-].

I've got the answers for each but I don't know if I'm correct and if I used correctly significant figures. Please, help!

Answer 1

Answer: -

1) Concentration of NaOH = 2.0 x 10⁻² M

Since NaOH is a monoacidic base,

The Hydroxide OH⁻ concentration will be the same as concentration of NaOH.

Concentration of hydroxide = [OH⁻] = 2.0 x 10⁻² M

We know the ionic product of water = 1.0 x 10⁻¹⁴

[H₃O⁺][OH⁻] = 1.0 x 10⁻¹⁴

Thus hydronium ion concentration [H₃O⁺] =
`(1.0 x 10^-14)/(2.0 x 10^ -2)`

= 5.0 x 10⁻¹³ M

2) Concentration of HNO₃ = 5.0 x 10⁻⁴ M

Since HNO₃ is a monobasic acid,

[H₃O⁺] = 5.0 x 10⁻⁴ M

pH = - log [H₃O⁺] = - log [5.0 x 10⁻⁴]

= 3.3

3) Concentration of Sr(OH)₂ = 3.45 x 10⁻² M

Since Sr(OH)₂ is a diacidic base,

Concentration of OH⁻ = [OH⁻] = 2 x 3.45 x 10⁻² M

We know the ionic product of water = 1.00 x 10⁻¹⁴

[H₃O⁺][OH⁻] = 1.0 x 10⁻¹⁴

Thus hydronium ion concentration [H₃O⁺] =
`(1.00 x 10^-14)/(2 x 3.45 x 10⁻² )`

= 1.45 x 10 ⁻¹³ M

pH = - log [H₃O⁺] = - log [1.45 x 10 ⁻¹³]

= 12.8

4) pH = 7.0

We know that [H₃O⁺] =
`10^(-pH)`

= 1.0 x 10⁻⁷ M

5) pH = 5.00

We know that [H₃O⁺] =
`10^(-pH)`

= 1.00 x 10⁻⁵ M

We know the ionic product of water = 1.0 x 10⁻¹⁴

[H₃O⁺][OH⁻] = 1.00 x 10⁻¹⁴

[OH⁻] =
`(1.00x10-14)/(1.00x10-5)`

= 1.00 x 10⁻⁹ M