Schweizer\'s reagent is a copper complex used for dissolution of cellulose. It i

Question

Schweizer's reagent is a copper complex used for dissolution of cellulose. It is prepared by precipitating copper(II) hydroxide, from an aqueous solution of copper(II) sulphate using sodium hydroxide, and then dissolving the precipitate in a solution of ammonia. Molar absorptivity of the copper complex in Schweizer's reagent at 620 nm is 3.0 times 10^4 Lcm^-1 mol^-1. An aqueous solution of this reagent showed a percent transmittance of 24.5% at 620 nm when measured in a 2.00 cm cell. (a) How many grams of solid CuSO_4.5H_2O are required to make 1.00 L of Schweizer's reagent solution? (b) What will be the percent transmittance of the same Schweizer's reagent solution at 620 nm, if a 1.00 cm cell was used?

Explanation / Answer

a)

A = e*l*M

A = (3*10^4)(2)*M

T = 24.5%

A = 2 - log10 %T

A = 2 - log(24.5) = 0.6108

find M

A = (3*10^4)(2)*M

0.6108 =  (3*10^4)(2)*M

M = (0.6108 ) /((3*10^4)(2)) = 0.00001018mol/L

now, change to mass

mol in 1 L = 0.00001018 mol

MW of Hydrate = CuSO4 + 5H2O = 159.609 + 5*18 = 249.609 g/mol

mass = mol*MW = (0.00001018)(249.609 ) = 0.00254 g of CusO4*5H2O

b)

find % T for a solution with

L = 1 cm

For the same data, find "l"

A = e*l*M

A = (3*10^4)(1)(0.00001018)

A = 0.3054

now change to T

A = 2 - log10 %T

0.3054 = 2- log(T%)

T% = 10^-((0.3054 -2)) = 49.9%

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