A 0.21g sample of sulfuric acid is dissolved completely in sufficient water to make 0.25 litre of final solution. Calculate the hydrogen ion concentration in mol1-1 in this solution and show successive steps in the calculation: If 0.21g in 0.25l then 0.84g in 1l. Add together molar masses 2x1.01 for hydrogen and 96.06 giving 98.08g molar mass. Number of moles in 0.84g is 0.84 divided by 98.08 giving 0.0085 mol. Would concentration then be 0.0085 mol litre-1 in one litre, divide this by 4 to get 0.25l giving 0.0021mol? I have no idea if I have worked this out correctly so any help would be appreciated!

I'm not sure if I was supposed to use mass numbers for each one added together e.g 1.01 H, 32.1 for S and 16.0 for O. I looked up the mass number for SO4 and used that!

You are ok down to 0.0085 mols/L H2SO4 (although I would have rounded to 0.0086M). You have two H ions that ionize so 0.00856 x 2 = ?? then round to two places.

I used 98.08 for molar mass H2SO4.

Thanks so much

0.0086 x 2 = 0.0172, so I now need to divide 0.0172 by four to give total amount in 0.25 litre? This gives 4.3-03, or 0.0043. Should I make the answer 0.004?

No on both counts. You have ALREADY used the 0.25 L.

0.21g x 1 molH2SO4/98.08 g = ??mols H2SO4.
??mols H2SO4/0.25 L = ?? mol/L H2SO4 = M

??mols/L H2SO4 x 2H^+/mol = (H^+) in mol/L. = 0.01713 mols/L = 0.01713 M.

That needs to be rounded to the correct number of significant figures.

I can't see where in my calculations I have used the 0.25l already. I thought I had worked out the concentration for 1 litre and needed to divide by 4 to get 0.25l giving 0.00214 mol. Now I'm really stuck! I'm teaching myself so I don't have anyone to ask for help!

A 0.21g sample of sulfuric acid is dissolved completely in sufficient water to make 0.25 litre of final solution. Calculate the hydrogen ion concentration in mol1-1 in this solution and show successive steps in the calculation: If 0.21g in 0.25l then 0.84g in 1l.You multiplied 0.21 g x 1/0.25L (or 0.21g x 4) = 0.84 g in 1 L here. So you have already corrected for the fact that the 0.21 was not in a liter). Add together molar masses 2x1.01 for hydrogen and 96.06 giving 98.08g molar mass. Number of moles in 0.84g is 0.84 divided by 98.08 giving 0.0085 mol.Then you divided the 0.84/molar mass to convert g/L to mols/L. Would concentration then be 0.0085 mol litre-1 in one litre, divide this by 4 to get 0.25l giving 0.0021mol? I have no idea if I have worked this out correctly so any help would be appreciated! This last step beginning with "Would......" was incorrect and the only thing you didn't do was to multiply the 0.0085 x 2 to account for the 2H^+ that ionize. If you do it through and let the numbers stay in the calculator (not rounding between steps) and round at thr end, you get 0.21/0.25L x 1/98.08 x 2 =
and that is the same as
0.21 x 4 x 1/98.08 x 2 =
which gives 0.01713 mols/L.
I hope this helps.

Thank you so much, I was getting a bit confused!

You've added up the mass wrong, it should be 98.12

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