Question

100ml of 0.2 N naoh is mixed with 100 ml 0.1N hcl and the solution is made 1litre.the ph of solution is

Answer 1

Answer: 12.7

Explanation: $Molarity =\frac{\text{Normality}}{n}}$

n= acidity (no of $OH^-$ ions)  or basicity  (no of $H^+$ ions)

${\text {Molarity of }NaOH}=\frac{0.2}{1}=0.2M$

${\text {Molarity of }HCl}=\frac{0.1}{1}=0.1M$

${\text{moles of solute}=\text{molarity}\times\text{Volume of solution in liters}}$

${\text{moles of NaOH}=\text{0.2M}\times\text{0.1L}}$ =0.02 moles

${\text{moles of HCl=\text{0.1M}\times\text{0.1L}}$ =0.01 moles

$HCl+NaOH\rightarrow NaCl+H_2O$

As 1 mole of HCl neutralizes 1 mole of NaOH, 0.01 moles of HCl will neutralise 0.01 mole of NaOH.

Moles of NaOH left unused= 0.01

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

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

$pOH=-log[OH^-]$

$pOH=-log[0.05]=1.30$

pH+pOH=14

pH=14-1.3=12.7