1.

(a) (i) What is crossed cannizaro reaction ? Explain it . (ii) Complete the following reaction . (b) (i) Is the following sugar , D - sugar or L - sugar ? (ii) Writer a not on vulcanization of rubber.

Answer»

Solution :(i) When Cannizaro reaction (Auto redox reaction ) takes place between two different aldehyde, the reaction is called as crossed cannizaro reaction .
`underset("Benzaldehyde")(C_6H_5CHO)+underset("formaldehyde")(HCHO)overset(NaOH)rarrunderset("Benzyl alchol")(C_6H_5CH_2OH)+underset("SODIUM formate")(HCOONa)`
In crossed cannizaro reaction more REACTIVE aldehyde is oxidized and LESS reactive .
(ii)
(b) (i) L - Sugar
(ii) 1. Natural rubber is very soft and brisky . it has high water absorption capacity and low tensile strength . Its properties can be improved by a process called vulcanization.
2. Natural rubber is mixed with 3-5% sulphur and heated at `100 - 150^@C` causes cross linking of the cis - 1, 4 polyisoprene chains through disulphide (-S-S-) bonds .
The physical properties of rubber can be altered by altered by controlling the amount of sulphur that is used for vulcanization . When 3 to 10% sulphur is used the resultant rubber is somewhat harder but flexible.
4. Following properties of rubber improved by vulcanization:
`"*"` Tensile strength
`"*"` Elasticity
`"*" ` HARDNESS
`"*"` Tear strength
`"*"` Resistance to solvents


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