The HCl solution taken 20mL 0.1M
The no. Of moles of HCl in this solution
The NaOH solution required for neutralisation of excess acid is 7.5mL 0.2M
The no. Of moles of NaOH in this solution
The equation of the acid base reaction is
This equation reveals that acid and base neutralises in 1:1 mole ratio.
Now equation of the reaction of Mg with HCl is
This equation reveals that HCl and Mg reacts completely with each other in mole ratio 2:1.
Hence the mass of Mg added to HCl solution was
where atomic mass of Mg