A) Be neutral
B) Be basic
C) Turn phenolphthalein solution pink
D) Turn methyl orange red
Correct Answer: C
Solution :
(i) \[20mL\]of \[0.5\,N\,HCl\] \[0.5N\] \[\Rightarrow \] \[1000mL\text{ }0.5\text{ }mol\text{ }HCl\]is present in \[20mL\] \[=\frac{20\times 0.5}{100}=1.0\times {{10}^{-2}}\] (ii) \[35ml\]of \[0.1N\text{ }NaOH\] \[0.1N\]\[\Rightarrow \] \[1000mL\]of \[0.1mol\]of \[NaOH\] \[\Rightarrow \] \[NaOH\]present in \[35mL=\frac{35\times 0.1}{1000}\] \[=0.35\times {{10}^{-2}}\] Total Volume \[=20+35=55mL\] \[\Rightarrow \]Resulting mole in solution, \[(1.0-0.35){{10}^{-2}}=0.65\times {{10}^{-2}}mol\,HCl\] \[HCl={{H}^{+}}+C{{l}^{-}}\] \[[HCl]=[{{H}^{+}}]+[C{{l}^{-}}]\] \[55mL\]contains \[0.65\times {{10}^{-2}}mole\]of \[{{H}^{+}}\] ions \[1000mL=\frac{0.65\times {{10}^{-2}}\times {{10}^{3}}}{55}=\frac{6.5}{55}\] \[pH=-\log [{{H}^{+}}]=-\log (6.5/55)\] \[=\log 55-\log 6.5=0.92\] Due to acidic nature of solution the colour of phenolphthalein becomes pink.
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