Amount of pure HCl = 0.42×1000=420kg.
Assumed reaction equation: 2NaCl+H₂SO₄➝2HCl+Na₂SO₄.
Approx atomic weights: Na=23, S=32, H=1, O=16, Cl=35.5.
Molecular weights: HCl=36.5, 2HCl=73, H₂SO₄=2+32+64=98, NaCl=58.5, 2NaCl=117, Na₂SO₄=46+32+64=142.
Reaction masses: 117+98➝73+142=215 for balance.
So 73/215 in the product is pure HCl and 98/215 in the reagents is pure H₂SO₄.
The ratio of the two acids is 73:98=HCl:H₂SO₄.
We know how much pure HCl there is so 73/98=420/x where x is the amount of pure H₂SO₄.
From this x=98×420/73=563.84kg approx.
But the H₂SO₄ solution is 90% pure acid, therefore 563.84 = 0.9y where y is the amount of acid solution.
y=563.84/0.9=626.48kg approx.