2 Hydrogen cyanide is a weak acid with a dissociation constant of ka= 4.0 x 10^-10 M . Write the dissociation equation for HCN.
a) calculate the concentration of Hydrogen ions, cyanide ions in HCN and the concentration of the compound, HCN at 0.100 M (mind the sig figs).
b) Wha is the pH of the solution?
4. Formic acid has the formula HCOOH and a Ka of 1.8 x 10^-4 M. It forms H+ and formate (HCOO-) ions on dissociation. A student is asked to prepare a buffer with a pH of 3.55 from a solution of formic acid and a solution of sodium formate with the same concentration. How many mL of NaFor solution should be added to 25 mL of the Hfor solution? Use the Henderson-Hasselbalch equation to solve.
5 When 5 drops of 0.2 M HCL were added to 25 mL of the buffer in the previous question, the pH decreased from 3.55 to 3.50. Write a net-ionic equation for the reaction which occurs when the acid is added to the buffer. If this component weren’t in the buffer, the pH would decrease by several whole units; this would in fact occur if that much HCL were added to 25 mL of H20).
Write net ionic equations to show why solutions of the compounds below are acidic or basic:
a) Na2CO3 is basic
b) NaHSO4 is acidic
c) NaC2H3O2 is basic
d) ZnCl2 is acidic
6 Calculate the pH from Ka
1.0 M acetic acid [acetate]= M [H+]= M M pH=
0.010 M acetic acid: [acetate]= M [H+]= M [pH]=
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