Question

what volume of hcl solution of density 1.2g/cm3 and containing 36.5% by weight hcl, must be allowed to react with zinc in order to liberate 4g of hydrogen

I know this calculate this part, but I do not get the answer 333.3ml

1.2g/ml x 1000 x 0.365/36.5 = 12M
or other calculation
0.365x 1200/36.5 =12M
But I do not understand to get 333.3ml answer Pls step by step for me

Answer 1

I did it step by step. Here it is again with more explanation. Write and balance the equation.
Zn + 2HCl ==> H2 + ZnCl2

How many mols H2 do you want to generate. mols = grams/molar mass
g H2 = 4g. molar mass H2 = 1*2 = 2 g/mol.
mol H2 = 4g/2 = 2 mols H2 in 4g H2.

Now convert mols H2 to mols HCl. That is done with the coefficient in the balanced equation.
2 mols H2 x (2 mols HCl/1 mol H2) = 4 mols HCl To obtain 4g H2 (2 mol) you will need 4 mols HCl.

How much 12 M HCl does it take to get 4 mol HCl? M HCl = mols HCl/L HCl or rearrange to L HCl = mols HCl/M HCl.
mols HCl = 4
M HCl = 12
L HCl = 4/12 = .3333L = 333.3 mL.

Answer 2

How 12 M came