What volumes of 12 N HCl and 3 N HCl must be mixed to form one litre 6 N HCl ?

Explanation

Let x mL of 12 N HCl and y mL of 3 N HCl be mixed to form one litre 6 N HCl.
So, x+y=1000.
Applying the formula `N_(1)V_(1)+N_(2)V_(2)=N_(3)V_(3)`,
`N_(1)=12 N, V_(1)=x, N_(2)=3 V_(2)=y, N_(3)=6, V_(3)=1000`
SO, `12x+3y=6xx1000`
Putting the value of y=(1000-x) from eq. (i) in eq. (ii),
12x+3(1000-x)=6000
or 12x-3x+3000=6000
or 9x=3000
`x=(3000)/(9)=333.3`mL
So, y=(1000-x)=(1000-333.3)=666.7 mL
i.e., 333.3 mL 12 N HCl and 666.7 mL 3 N HCl are mixed.