pH and Buffer questions
Chemistry

Tutor: None Selected  Time limit: 1 Day 
Calculate the pH of the following solutions. Show work pls
0.0893 M HBr
1.2 x 10 4 M NaOH
buffer containing 0.150 M HC2H3O2 and 0.050 M C2H3O2
In solution,
HBr + NaOH ==== Na+ + Br + H2O
So the 1.2 x 10 4 M OH in NaOH will be completely neutralized by the H+ in HBr, which makes the concentration of H+ in the solution at this point:
[H+]=0.0893 1.2 x 10 4 =0.08918 M
Now we can think about the buffer.
HC2H3O2 ==== H+ + C2H3O2 pKa=4.76
So when the above reaction reaches its balance,
[H+][C2H3O2]/[HC2H3O2 ]=10^4.76=1.74 x 10 5
Since now
[H+][C2H3O2]/[HC2H3O2 ]=0.08918 x 0.05 /0.15 = 0.02973 >> 1.74 x 10 5
So the reaction will move in the left direction. Assuming a M H+ is converted to HC2H3O2 to reach the final balance, we can now get the following equation
(0.08918a) (0.05a) / (0.15 + a) = 1.74 x 10 5
(0.08918a) (0.05a) = 1.74 x 10 5 (0.15 + a)
a^20.139a+0.004456=0
Since a has to be not larger than 0.05, so after the calculation you will find that a=0.05, which means all C2H3O2 is converted to HC2H3O2 at the end.
Therefore the final concentration of H+
[H+] = 0.089180.05 = 0.03918 M
pH = 1.4
Secure Information
Content will be erased after question is completed.