[mol]

A solution of 10 g of formic acid and 10 g of potassium formate dissolved in 1.00 L of H2O.
what is the pH of the buffer solution?

For this I calcualted the M for formic acid as 0.217M; but for the potassium formate should I take into account the whole compound as 10/85 =0.147 M or should I calcualte the mass for only the negative acetate ion as 10/45 =0.222 M.
so that I can substitute those M values in
                                                                      formate ion M times H+ ion M
                                                           Ka  =  ------------------------------
                                                                       formic acid M

The text says the value as
                                                               (.417) (H+)
                              Ka=  1.8* 10^-4 =   --------------------
                                                              .217

I got the M for formic acid correct but not the .417 M for acetate ion. How to do this calcultion for M =mass/molarmass? For molarmass value should I consider the potassium too?
Any help pls....

[jam]

M is the abbreviation or symbol for the unit of molar concentration. The symbol for the quantity itself is c, as in c = n/V.
If you found a bottle of pure formate ions, you could weigh 10 g of them.  You won't find one, so you'll have to stick to the information given in the problem, weigh out potassium formate, and use the stoichiometric conversion factor that dissolution and dissociation of one mole of potassium formate produces one mole of formate ions in solution.

[Borek]

10/85 =0.147

Replace batteries in your calculator.

The text says the value as (...) .417 M for acetate ion.

This is about as wrong as the value you have calculated. No idea what is going on, but both 0.147M and 0.417M are wrong. At first I thought it is just a typo (1 and 4 switched positions), but it is not.

[mol]

Hi Borek
I am sorry I made the typo here n not my calculator.lol
u r right.it is 0 .117
But thats not my issue. i couldnt understand how the .417 value is given in the text? I too get it that the value is wrong. But is there anyway you could help by solving this calculation pls?
thanks

[Borek]

You are on the right track with concentratiopn calculations. Use Henderson-Hasselbalch equation. SImple plug and chug.

And please don't use textese on the forums. Thats against forum rules.

[mol]

Thank you jam n Borek. Sure I will be more careful in my future postings.