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Q.
If pH of the solution is one, what weight of $HCl$ present in one litre of solution?
Equilibrium
Solution:
$pH =1$
$pH=-\log \left[H^{+}\right] \Rightarrow\left[H^{+}\right]=10^{-pH}$
$10^{-1} M =10^{-1}$ moles/lit
The mass of $1$ mole of a substance in grams is called its molar mass.
Hence, (molar mass of $HCl$ is $36.5) 1$ mole $HCl =36.5\, g$
$1\, mole HCl =36.5 \times .1=3.65\, g$