Question

a. You procured a potash fertiliser which was guaranteed to contain 50% K. Calculate the content as K₂O. [At. Wts.: K=39, O=16].

b. A phosphate fertiliser contains 45% P₂O₅. To what percent of P does this correspond? [At.Wts.: P=31. K=39, O=16].

Answer 1

Ans

a)

Let the fertliser be 100 g

so K will be 50 g

50 g K = 50/39 = 1.282 moles

So number of moles of O = 1.282 /2 = 0.641 moles

0.641 moles of O = 0.641 x 16 = 10.256 g

Total amount of K2O = 50 + 10.256 = 60.256 g

So the content in fertiliser = (60.256 / 100) x 100

= 60.256 %

b)

Let the fertiliser be 100 g

so P2O5 = 45 g

The molar mass of P2O5 = (31 x 2) + (16 x 5) = 142 g/mol

142 g of P2O5 has 62 g of P

So 45 g of P2O5 will contain (45 x 62) / 142 = 19.65 g of P

19.65 g of P will be ( 19.65 x 100) / 100

= 19.65 % of P in phosphate fertiliser