Equilibrium Question 417
Question: $ 20ml $ of $ 0.5N,HCl $ and $ 35,ml $ of $ 0.1N,NaOH $ are mixed. The resulting solution will [KCET 2005]
Options:
A) Be neutral
B) Be basic
C) Turn phenolphthalein solution pink
D) Turn methyl orange red
Show Answer
Answer:
Correct Answer: C
Solution:
(i) 20 ml of 0.5 N HCl $ 0.5N\Rightarrow 1000,ml,0.5,mole,HCl $ is present in $ 20,ml $
$ =\frac{20\times 0.5}{1000}=1.0\times {10^{-2}} $ (ii) 35 ml of 0.1 N NaOH $ 0.1N\Rightarrow 1000ml $ of 0.1 mole $ NaOH $ is 35 ml $ =\frac{35\times 0.1}{1000}=0.35\times {10^{-2}} $ Total = 20 + 35 = 55 ml.
$ \Rightarrow $ (1.0-0.35)10-2=0.65 ´ 10-2mole HCl HCl = H++Cl-
$ \Rightarrow $ [HCl] = [H+]+[Cl-] 55 ml contains 0.65 ´ 10-2 mole of H+ ions $ 1000,ml-\frac{0.65\times {10^{-2}}\times 10^{3}}{55}=\frac{6.5}{55} $
$ pH=-\log [{H^{+}}]=-\log (6.5/55) $
$ =\log 55-\log 6.5=0.92 $ Due to acidic nature of solutions the colour of phenolphthalein becomes pink.
