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 \[HCl\] \[0.05\Rightarrow 1000\,mL\,0.5\,mol\,HCl\] is present in 20 mL \[=\frac{20\times 0.5}{100}=1.0\times {{10}^{-2}}\] (i) 35 ml of 0.1 N \[NaOH\] \[0.1\,N\Rightarrow 1000\,mL\] of 0.1 mol of \[NaOH\] \[\Rightarrow NaOH\] present in \[35\text{ }mL\text{ }=\frac{35\times 0.1}{1000}\] \[=0.35\times {{10}^{-2}}\] Total Volume = 20 + 35 = 55 mL \[\Rightarrow \] Resulting mole in solution, \[(1.0-0.35)\,{{10}^{-2}}=0.65\times {{10}^{-2}}mol\,HCl\] \[HCl={{H}^{+}}+C{{l}^{-}}\] \[[HCl]=[{{H}^{+}}]+[C{{l}^{-}}]\] 55 mL contains \[0.65\times {{10}^{-2}}\] 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 solution the colour of phenolphthalein becomes pink.
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