By adding 20 mL of 0.1 N HCI to 20 mL of 0.001 N KOH, the pH of the obtained solution will be

We know that, 20 mL of 0.1 N HCI containsH+=201000×0.1=2×10−3mol Similarly, 20 mL of 0.001 N KOH contains OH−=201000×0.001=2×10−5mol H+in the mixture =2×10−3−2×10−5 =1.98×10−3 H+=1.98×10−340×10−3=4.950×10−5 pH=−log⁡H+ =−log⁡4.950×10−5 =−log⁡4.950−log⁡10−5 =−log⁡4.950−(−5)log⁡10 pH=−3.6946+5=1.3