Thermal Analysis 1.(a) The figure below was obtained by subjecting CuSO4·nH2O to

Question

Thermal Analysis

1.(a) The figure below was obtained by subjecting CuSO4·nH2O to thermal gravimetric analysis(TGA). The transition from A toD represents the loss of all water of crystallisation. The sample masses at points A and D were 12.484 and 7.980mg respectively. Estimate the value of n at each of the point A,B,C and D.

(b?What are the main differences between differential thermal analysis(DTA) and differential scanning calorimetry(DSC). Include in your answer the different instrumentation and different results obtained.

Explanation / Answer

1. (a) Given total weight loss for TGA,

A to D = 12.484 mg - 7.980 mg = 4.504 mg is the mass of H2O in the sample

molar mass of CuSO4.5H2O = 249.72 g/mol

molar mass of H2O = 18.02 g/mol

moles of CuSO4.5H2O sample = 12.484 mg /249.72 g/mol = 0.05 mmol

moles of H2O in sample = 4.504/18.02 g/mol = 0.25 mmol

A to B is 45% weight loss, B to C is 30% weight loss and C to D is 25% weight loss

So,

at A n = 5

at B n = 4.504 - 0.45 x 4.504 = 2.5 or 3

at C n = 4.504 - 0.75 x 4.504 = 1

at D n = 0

(b) DSC is differential scanning calorimetry which measures the change in phase of the sample with respect to a standard with temperature. DTA on the other hand measures the change in weight of sample with respect to time with temperature and an standard reference.  

Calculations are as folows

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