Question

Sulfur Determination in Coal Samples experiment

i)The coal sample being used in this experiment is assumed to have 3% sulfur in its composition. What percent of sulfate (SO₄^2-) is present in the coal samples?

ii) Knowing the percent of assumed sulfate from above in your coal samples, what would be the concentration of sulfate (in ppm) if the sample was placed in 250 mL of water?

iii) The UV-Vis spectrophotometer and the Ion Chromatograph (IC) have both been introduced in earlier experiments in this course. Based on your prior knowledge of these instruments, which do you think will give a more accurate reading of sulfate levels in your coal samples? Why?

Answer 1

1. i.

Its given in the question % of Sulfur in the samole is 3%

and we can find % by weight of Sulfure in SO₄^2- is 32/(32+64)*100=33.33%

And we know that in sample % of sulfur is 3%

therefore %of SO₄^2- in sample is (3/100)*33.33=0.999%

ii.As we know that

1% = 10000ppm

Therefore 0.99% of SO₄^2- corresponds to 9999ppm

iii.UV-Vis spectrophotometer will be more accurate for reading of sulfate levels in coal samples than Ion Chromatograph (IC) ,it is because  UV-Vis spectrophotometer utilises concept of absorption of UV light for molecules containing pi-electrons e.g.Sulfur and based upon the absorption characterstics it can calculate its reading accurately while Ion Chromatograph (IC) is used to separate polar molecules and here in the sample there can be more than one polar species present and it can become difficult for it to separate completely SO4^2- and give its reading accurately.