Anchem 15/16 Q4 Please show the answer clearly and in detail. A sample of sodium

Question

Anchem 15/16 Q4

Please show the answer clearly and in detail.

A sample of sodium sulfate is known to be contaminated with copper(II) ions. Analysis of standardized copper(II) solutions at known concentrations gave the following calibration curve: y is the absorbance at 453 nm and x is the concentration of Cu(II) in ppm. Under the same conditions, a solution made by dissolving 1.00 g of the sodium sulfate sample in 1.00 dm^3 distilled water gave an absorbance value of 0.200. a) Calculate the transmittance of the diluted sodium sulfate solution. b) Determine the concentration (ppm) of Cu(ll) in the sodium sulfate sample and estimate the purity of this solid sodium sulfate sample in weight/weight percent. c) Explain in detail why the absorbance value of Cu(II) solutions deviate from linearity when the concentration of Cu(II) is higher than 30 ppm.

Explanation / Answer

From the given data

a) Absorbance = 2 - log(%T)

for diluted Na2SO4, absorbance = 0.200

log(%T) = 2 - 0.200

Transmittance = 0.631

b) Cu(II) concentration in Na2SO4 sample with absorbance 0.2 = 10 ppm from graph

concentration in Na2SO4 in ppm = 1 x 1000/0.1 = 10,000 ppm

w/w% Cu(II) in Na2SO4 sample = 10/10,000 = 0.001%

c) The Beer's law is applicable for dilute solutions only. When the concentration is much higher like Cu(II) solution with higher than 30 ppm, the solution absorbs most of the light and transmittance is almost negligible. So the experimental values are not reliable under these higher concentrations.

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