Kerala Board Solutions for Chapter: Redox Reactions and Rate of Chemical Reactions, Exercise 3: Extended activities

Find the oxidation number of the elements which are underlined in the compounds given below. Among these find out the elements which show variable oxidation numbers.
$\underset{\mathrm{\_\_\_}}{\mathrm{Mn}}{\mathrm{O}}_2, \underset{\mathrm{\_\_\_}}{{\mathrm{Mn}}_2}{\mathrm{O}}_7, {\mathrm{K}}_2\underset{\mathrm{\_\_}}{{\mathrm{Cr}}_2}{\mathrm{O}}_7, \mathrm{K}\underset{\mathrm{\_\_}}{\mathrm{Cr}}{\mathrm{O}}_3, \underset{\mathrm{\_\_\_}}{\mathrm{Mn}}{\mathrm{Cl}}_2, \underset{\mathrm{\_\_\_}}{\mathrm{Mg}}\mathrm{O}, \underset{\mathrm{\_\_\_}}{\mathrm{Mg}}{\mathrm{Cl}}_2, \underset{\mathrm{\_\_}}{{\mathrm{Al}}_2}{\mathrm{O}}_3, \underset{\mathrm{\_\_}}{\mathrm{Al}}{\mathrm{Cl}}_3\mathbf{ }$
(Hint. Oxidation number $\mathrm{O}=-2, \mathrm{Cl}=-1, \mathrm{K}=+1$)

Some apparatus and chemicals are given.
$\mathrm{Zn}, \mathrm{Mg},$ dilute $\mathrm{HCl}, {\mathrm{CaCO}}_3,$ test tube, water.
a) Design an experiment to prove that the nature of reactants can influence the rate of reaction.
b) Write the equations for the chemical reactions.
c) Write the expression for the rate of the reaction.

The experiments conducted by two students are given below.
Experiment I: $2 \mathrm{ml}$ of sodium thiosulphate solution is taken in a test tube, heated and to it $2 \mathrm{ml}$ of $\mathrm{HCl}$ solution is added.
Experiment II: $2 \mathrm{ml}$ of sodium thiosulphate solution is taken in a test tube and to it $2 \mathrm{ml}$ of $\mathrm{HCl}$ solution is added.
a) In which experiment is the precipitate formed quickly? Justify your answer.
b) Write the balanced equation for the reaction.

Some materials available in the laboratory are given below. Magnesium ribbon, marble powder, marble pieces, dilute $\mathrm{HCl}$, concentrated $\mathrm{HCl}$.
a) Which materials will you choose for the preparation of more ${\mathrm{CO}}_2$ in less time?
b) Write the balanced chemical equation of the reaction.