Question

what is the concentration of hydrogen ions in 0.05 mol/dm3 sulfuric acid

Answer 1

0.05mol H2SO4/dm^3 * 2mol H+/mol H2SO4 * 1g H+/mol H+ = 0.10g/dm^3 

It's just a matter of converting units. For every mole of sulfuric acid, there are 2 moles of hydrogen ions, and for every mole of hydrogen ions, there is one gram of hydrogen ions.