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(a). What is the average molecular mass ...

(a). What is the average molecular mass of starch?
(b). What is the approximate average number of glucose units in the sample of starch?
`(Given: 20 gm L^(-1)` of starch has an osmotic pressure `=10^(-2) atm at 25^(@)C.)`

Text Solution

Verified by Experts

(a). `pi=MRT("M=molarity of solution")`.
`M=(pi)/(RT)=(10^(-2)atm)/((0.082"L atm mol"^(-1)K^(-1))(298 K))=4xx10^(-4)M`.
`M=(W_(2)xx1000)/(MW_(2)xx"vol. Of sulution in ml")`
`MW_(2)=(20xx1000)/(4xx10^(-4)xx1000)=5xx10^(4)"gm mol"^(-1)`
(b). Strach is a polymer of glucose, each glucose unit `("MW of glucose=180 gm mol"^(-1))` is joined to another glucose unit with loss of one `H_(2)O` unit `(18 gm mol^(-1))` giving a `MW` of `180-18=162 gm mol^(-1)` per unit.
:. Number of glucose units
`=(5xx10^(4) "gm mol"^(-1))/(162 "gm mol"^(-1) unit^(-1))`
`=309~~310` glucose unit.
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