PH question!?
Answer:
Solution of weak acid (HCN) and its salt (Ba(CN)2) is called buffer and pH is calculated by using this formula (equation)
15.2 from the site below
http://www.chembuddy.com/?left=ph-calcul...
In your problem pKa of HCN is 9.40( is tabulated value, I got it from here http://daecr1.harvard.edu/pdf/evans_pka_...
conc of A anion is 2*0.025M =0.05M (your salt is Ba(CN)2 which gives 2* conc of ions when dissolved in water, because it dissociates completely, strong electrolite), and HA, concentration of weak acid is 0.05M. When you plug numbers in the formula you'll get pH=pKa=9.40
Are you sure that 9.4 is the answer?
If so, 9.4 would be the -log of the concentration of H+ ions. By solving -log (x) = 9.4, there must be a concentration of 3.98 x 10^-10 M of H+ ions. That doesn't seem consistent with the data, but if 9.4 is the answer, that must be the [H+] of the solution.
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