Question

Question 8 A chemist dissolves of pure potassium hydroxide in enough water to make up of solution. Calculate the pH of the solution. (The temperature of the solution is .) Round your answer to significant decimal places.

Answer 1

The question is incomplete, here is the complete question:

A chemist dissolves of 716. mg pure potassium hydroxide in enough water to make up 130. mL of solution. Calculate the pH of the solution. (The temperature of the solution is 25°C.) Round your answer to 2 significant decimal places.

Answer: The pH of the solution is 13.14

Explanation:

To calculate the molarity of solution, we use the equation:

$\text{Molarity of the solution}=\frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}$

Given mass of NaOH = 716 mg = 0.716 g    (Conversion factor:  1 g = 1000 mg)

Molar mass of NaOH = 40 g/mol

Volume of solution = 130 mL

Putting values in above equation, we get:

$\text{Molarity of NaOH}=\frac{0.716\times 1000}{40\times 130}\\\\\text{Molarity of NaOH}=0.138M$

1 mole of NaOH produces 1 mole of $Na^+$ ions and 1 mole of $OH^-$ ions

To calculate the pOH of the solution, we use the equation:

$pOH=-\log[OH^-]$

We are given:

$[OH^-]=0.138M$

Putting values in above equation, we get:

$pOH=-\log(0.138)\\\\pOH=0.86$

To calculate pH of the solution, we use the equation:

$pH+pOH=14\\pH=14-0.86=13.14$

Hence, the pH of the solution is 13.14