Question

calculate the pH of 0.4g of NaOH dissolved in water to give 200 ml of solution.

Answer 1

pH=14-log(concentraiionOH)
but concentration of OH is moles/liters
OH concentration= (.4g/40g/mole)/.2liters = 50 mol / m^3
now,14- log(50)=12.3010299957

Answer 2

Answer: pH is 12.7

Explanation: To calculate the moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\textMolar mass}}$

For NaOH

Mass  given = 0.4 g

Molar mass = 40 g/mol

Putting values in above equation, we get:

$\text{Moles of} NaOH=\frac{0.4g}{40g/mol}=0.01mol$

$Molarity=\frac{\text {no of moles}}{\text {Volume of solution in L}}$

$Molarity=\frac{0.01}{0.2 L}=0.05M$

$NaOH\rightarrow Na^++OH^-$

0.05 moles of NaOH gives 0.05 moles of $OH^-$ ions.

$pOH=-log[OH^-]=-log[0.05]=1.30$

$pH = 14 - 1.30= 12.7$