1.

A certain mixture of HCl and CH_3-COOH is 0.1 M in each of the acids.20 ml of this solution is titrated against 0.1M NaOH.By how many units does the pH changes form the start to the stage when the HCl is almost completely neutralised ? K_a for acetic acid=1.8xx10^(-5).

Answer»

2.03
0.775
2.325
3.175

Solution :INITIAL `[H^+]`=0.1 (`H^+` from weak acid can neglect )
After NEUTRALISATION of HCl volume would double, HENCE concentration of `CH_3COOH=(0.1xx20)/40=0.05`
`[H^+]=sqrt(K_aC)`
`[H^+]=sqrt(1.8xx10^(-5)xx0.05)=9.48xx10^(-4)`
pH=3.03
change in pH unit =3.03-1=2.03


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