A-Level Trends in the elements across a period and down a group: worked solution

Question

With reference to section 24 of the data booklet, deduce how the reducing power of the group 17 halide ions compares, and justify your answer.

Reducing power is the tendency to be oxidised (to lose electrons). From section 24, E-plimsoll for the X2/2X- half-cells is: F2/F- +2.87 V, Cl2/Cl- +1.36 V, Br2/Br- +1.07 V, I2/I- +0.54 V. The E-plimsoll value becomes less positive down the group, so the halide ion is more readily oxidised back to the halogen down the group. Hence reducing power increases down group 17: I- > Br- > Cl- > F-, with I- the strongest reducing agent.