Should 25 ml of 0.15 M HCL solution be added to 250 mL of buffer solution containing 0.25M HF Ka-7.1 x 10, and 0.40 M NaF at a pH of 3.15 what is the new pH?

Answer 1

millimols NaF = mL x M = approx 100
mmols HF = mL x M = aprox 62.5
mmols HCl added = approx 3.75

You omitted the exponent on Ka. I think that's 7.1E-4, then pKa = 3.14

................F^- + H^+ ==> HF
I..............100....0.......62.5
add.................3.75
C...........-3.75..-3.75......+3.75
E............96.25....0.......66.25
Substitute the E line into HH equation and solve for pH. On the surface it sounds like much too much HCl is added; however, the pH shows there is enough buffer capacity there to handle it (and more).

Answer 2

For the formula pH=pka + log(base/acid)
Which would be the base and which would be the acid? Thanks.

Answer 3

NaF is the base
HF is the acid.

Answer 4

Thank you so much!

Answer 5

Would HCL be put on the bottom with HF because it's an acid also?