A) Be neutral
B) Be basic
C) Turn phenolphthalein solution pink
D) Turn methyl orange red
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.
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