Question

Give reasons in one or two sentences for each of the following: 

(i) Graphite is used as a solid lubricant. 

(ii) Fluorine cannot be prepared from fluorides by chemical oxidation.

Answer 1

(i) In graphite, hexagonal planes are held by weak van der Waals' forces. Since these forces are overcome, one plane slides over the other. This explains the lubricating properties of graphite. 

(ii) Fluoride has negative oxidation potential

2F^- → F₂ + 2e^-, E_OP = - 2.87V

Hence, fluoride is the poorest reducing agent.

Hence, F₂ cannot be prepared by oxidation of HF by even strong oxidising agents such as KMnO₄, MnO₂ etc.