Page 77 - Analytical Chemistry I E-book

• Back titrations: Sample (X) reacts with titrant (Y) but for any reason,
direct titration cannot be done (for example reaction is slow or
reversible). So accurately measured excess of titrant (Y) is added to
the sample, leave them enough time for complete reaction, then the
remaining unused excess of titrant (Y) is titrated against another titrant
(Z).

Step 1: Sample (X) + Known excess of titrant (Y), leave for some time.
Step 2: Unused excess of titrant (Y) # titrant (Z).

• Example: measured excess of titrant Y = 50 mL
EP = Unused (unconsumed) excess of titrant Y = 20 mL
Sample = Total – EP = 50 – 20 = 30 mL