Question

What is the need to use spectroscopy to determine the percent yield of a product? What is the difference to determine the percent yield in experiments such as (Inorganic Synthesis) or 8 (Organic Synthesis)?

Consider the measured absorbance of your product. Did this value fall somewhere between the range of concentrations of standard solutions you prepared to make your calibration curve? Why is it important that it is?

When performing a linear fit to data, a perfect fit will have a correlation of 1; in reality, good data typically has a correlation of at least 0.99, and exceptional data has a correlation of greater than 0.999. Consider your value of the correlation obtained in the linear fit to your calibration curve, and comment on how closely your data points matched the linear fit.

Use the slope of your linear fit to determine the molar absorptivity, ε, for copper (II) sulfate; include units with your value, noting that absorbance is a unitless value.

Would you expect the molar absorptivity to be a different value if you had measured absorbance of all solutions at, say, 400 nm instead of 650 nm? Consider your full spectrum curve of Solution A. Explain why or why not.

Answer 1

a.With the use of Spectroscopy %of yield of products can be determined previously. Chance of error will be less if we use spectroscopy instate of titrimetric method. Various spectroscopic methods like ultraviolet spectroscopy, Atomic absorption Spectroscopy, Infrared Spectroscopy, XRF, XRD etc.If we use Gas Chromatography or HPLC in conjunction with spectroscopy will leads to more accurate determination of percentage of yield.

b. In case of Inorganic Synthesis ultraviolet spectroscopy will be the more suitable tool to use. For organic synthesis Gas Chromatography or HPLC in conjunction with FT- IR or FT- NMR spectroscopy will leads to more accurate results.

c. Measured absorbance value of the synthesis product must fall somewhere between the range of concentration of standard solutions use to prepare calibration curve, otherwise there will be error in analysis as the lineraity of the curve will not be maintained.

d. A= €.c.l

Where A= absorbance, €=molar absorptivity, c= concentration of the solution, l= length of the path length of the light

Thus if we plot A vs c at a constant l and at a particular wavelength then we get a straight line with slope= molar absorptivity,

From the value of slope molar absorptivity of copper (II) sulphate can be determined.

d. Molar absorptivity will be different if we change the wavelength from 400 nm to 600 nm. Because Lambert beer's law A=€.c.l is valid at a particular wavelength. Thus at a particular wavelength value of molar absorptivity i.e € is constant and absorbance , A will be proportional to concentration, C . If wavelength is changed then value of molar absorptivity will also be changed.