20 ml of 0.5 N HCl and 35 ml of 0.1 N NaOHare mixed. The resulting solution will

Options

A. be neutral
B. be basic
C. turn phenolphthalein solution pink
D. turn methyl orange red

Answer

c

Explanation

(i) 20 ml of 0.5 N HCI
`0.5 N implies` 1000 ml 0.5 mole HC l is present in`20ml=(20xx0.5)/(1000)=1.0xx10^(-2)`
(ii) 35 ml of 0.J N NaOH
0.1 N implies 1000 ml of 0.1 mole of NaOH
`implies35ml=(35xx0.1)/(1000)=0.35xx10^(-2)`
Total `= 20 + 35 = 55 ml`
` implies (1.0 - 0.35)10^(-2) = 0.65 xx 10^(-2) mole HCI`
`HCI = H^(+) + CI^(-)`
`implies[HCI] = [H\^(+)] + [CH^(-)]`
55 ml contains `0.65 xx 10^(-2)` mole of `H^(+)` ions
`1000ml-(0.65xx10^(-2)xx10^(3))/(55)=(6.5)/(55)`
`pH=-log[H^(+)]=-log(6.5//55)`
`=log55-log6.5=0.92`
Due to acidic nature of solution the colour of phenolphthalein becomes pink.