Table 13.1 gives some properties and uses of three halogens. Table 13.1 Element Colour A use chlorine bromine red-brown making chemicals iodine as an antise...

This question combines the properties, uses and displacement reactions of the halogens. Chlorine, bromine and iodine sit in Group VII, and their reactivity decreases down the group.

(a) The completed cells are [3] (one mark each):

Chlorine colour = pale green [1]; use of chlorine = sterilising water (or making bleach, or making hydrochloric acid) [1]; iodine colour = grey-black [1].

(b) Chlorine is used to treat drinking water because it kills bacteria / microorganisms [1].

(c) An antiseptic kills bacteria / microorganisms (on the skin) [1].

(d) The general name for these Group VII elements is the halogens [1].

(e) Reactivity decreases going down Group VII [1].

(f) Adding aqueous bromine to potassium iodide: the colourless solution turns brown [1] as iodine is formed [1], because bromine is more reactive than iodine and displaces it.

(g) Word equation: bromine + potassium iodide → potassium bromide + iodine [1].

(h) Iodine cannot displace bromine because iodine is less reactive than bromine [1]; a halogen can only displace one below it in the group.

(i) A safety precaution with chlorine gas: use a fume cupboard (also acceptable: do not breathe the gas, or wear eye protection) [1].

(j) Astatine is below iodine, so with even higher melting and boiling points it is a solid at room temperature [1].

Exam tip: learn one everyday use per halogen (chlorine for water treatment, iodine as an antiseptic) and pair every displacement with "more reactive pushes out less reactive".