Question

The pH at the equivalence point of a titration of an unknown monoprotic substance with a strong titrant is determined to be 6.63. Based on this pH value, explain whether the unknown substance is a strong acid, strong base, weak acid, or weak base.

A chemist wants to perform a reaction at pH = 8.3 so they attempt to make a buffered solution. For this buffer, the chemist dissolves 12.5 moles of methylammonium, CH₃NH₃⁺, (K_a = 2.3 x 10^–11) and 0.057 moles of methylamine, CH₃NH₂, into 1 L of water. Explain whether this solution would be an effective buffer for the reaction. Why or why not?

Answer 1

The Less till pH at than f acidic. the equivalence point is 6.63 which is ire the solution at equivalence point is so the acid must be a Strong acid. So, the unknown Substance is a strong acid. a pH of the buffer should be 8.3. we know pH = pka + log [salt I Cacid] CH₂ Bug is weak acid conjugate base which is buffer solution: and CH3NH2 is it's strong. So it can form ka = 2.3415 :pka = 10.638. 1 L = 1000 me. pH = pkat w [CH3NH2] [CHANH * 10.638 + (0.057/1000) (12.5/1000) - 8.2969. So pH = 8.2969 is very much close to 8.3. So the this solution would reaction. be an effective buffer fon.