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Q.
$ pH $ or $ 1L\,0.1\,M\,HCl $ when $5\, g$ of $HF$ is added:
Delhi UMET/DPMTDelhi UMET/DPMT 2006
Solution:
$pH$ of mixture of strong and weak acid depends only upon strong acid concentration.
$0.1 \,M \,HCl=0.1 \,NHCl$ its $\left[H^{+}\right]=0.1$
$ p H=-\log \left[H^{+}\right]=\log \frac{1}{\left[H^{+}\right]}$
$=\log \frac{1}{[0.1]} =\log 10=1$