Question

PH is a logarithmic scale used to indicate the hydrogen ion concentration, [H+], of a solution: pH=−log[H+] Due to the autoionization of water, in any aqueous solution, the hydrogen ion concentration and the hydroxide ion concentration, [OH−], are related to each other by the Kw of water: Kw=[H+][OH−]=1.00×10−14 where 1.00×10−14 is the value at approximately 297 K. Based on this relation, the pH and pOH are also related to each other as 14.00=pH+pOH.
The temperature for each solution is carried out at approximately 297 K where Kw=1.00×10−14.

a. 0.40 g of hydrogen chloride (HCl) is dissolved in water to make 4.5 L of solution. What is the pH of the resulting hydrochloric acid solution?
b. 0.80 g of sodium hydroxide (NaOH) pellets are dissolved in water to make 2.0 L of solution. What is the pH of this solution?

Answer 1

Answer:

a. 2.6

b. 12.0

Explanation:

a.

First, we will calculate the molar concentration of HCl.

M = mass of HCl / molar mass of HCl × liters of solution

M = 0.40 g / 36.46 g/mol × 4.5 L

M = 2.4 × 10⁻³ M

HCl is a strong monoprotic acid, so [H⁺] = 2.4 × 10⁻³ M. The pH is:

pH = -log [H⁺]

pH = -log 2.4 × 10⁻³ = 2.6

b.

First, we will calculate the molar concentration of NaOH.

M = mass of NaOH / molar mass of NaOH × liters of solution

M = 0.80 g / 40.00 g/mol × 2.0 L

M = 0.010 M

NaOH is a strong base with 1 OH⁻, so [OH⁻] = 0.010 M. The pOH is:

pOH = -log [OH⁻]

pOH = -log 0.010 = 2.0

The pH is:

14.00 = pH + pOH

pH = 14.00 - pOH = 14.00 - 2.0 = 12.0