Hi, I've been trying to solve a certain question for about an hour now, and I just can't get it right. The question is:
Arrange the following mixed solutions A, B and C in order of decreasing value of pH:
A: 15 ml of 0.1 mol/l H2SO4 and 10 ml of 0.1 mol/l NaOH.
B: 15 ml of 0.1 mol/l HCl and 10 ml of 0.1 mol/l Na2CO3.
C: 15 ml of 0.1 mol/l HCl and 10 ml of 0.1 mol/l NaOH.
Now, no matter how many times I revise, the answer I get is B = C > A, while the correct answer according to the answers page is B > C > A.
In A I found that there are 0.003 moles of H30+ from the H2SO4 and 0.001 moles of 0.001 OH- from the NaOH. So I concluded that there is in total 0.002 moles of H30+.
In B I found 0.0015 moles of H30+ from HCl and 0.001 moles of OH- from the Na2CO3, so in conclusion there are 0.0005 moles of H30+.
In C I found 0.0015 moles of H30+ from HCl and 0.001 moles of 0.001 OH- from the NaOH, so in conclusion there are 0.0005 moles of H30+.
Now, because the volume of all solutions are the same, the less the quantity of H30+, the larger the pH, so I found B = C > A.
If someone can please check my answer, and see if it's correct it'll be very much appreciated!
Thanks.