Question

Two 23.0 mL samples, one 0.200 MKOH and the other 0.200 M CH3NH2, were titrated with 0.100 MHI. Answer each of the following questions regarding these two titrations.

a). What is the volume of added acid at the equivalence point for CH3NH2?

b). Predict whether the pH at the equivalence point for each titration will be acidic, basic, or neutral.

c). Predict which titration curve will have the lowest initial pH.

Answer 1

a) moles CH₃NH₂ = 0.0230 L * 0.200 mol /L = 0.0046 mol

so, moles HI required = 0.0046 mol

Now, volume of HI added at the equivalence point = 0.0046 mol / 0.100 mol/L = 0.0046 L = 46 mL.

b) At the equivalence point,

strong base (KOH) + strong acid (HI) implies pH = 7.0 . Therefore , it will be neutral.

and CH₃NH₂(weak base) + strong acid (HI) implies pH < 7. Therefore , it will be acidic.

c) KOH OH^- + K⁺ . It will have lower pH.

CH₃NH₂ + H₂O OH^- + CH₃NH₃⁺. It will have higher pH.