chemistry nov03 paper 1 problems

[avnidhunnoo]

a garden fertiliser is said to have a phosphorus content of 30% 'P2O5 soluble in water'.
what is the percentage by mass of phosphorus in the fertiliser?
Ans : 13.1%

how to do this calculation please?

 

[anahita16]

Mr of P2O5 = 2(31)+5(16)=142

Percentage by mass of P in P2O5 = (62/142)*100 %

Percentage by mass of P in fertiliser= 0.30 * (62/142)*100=13.1%

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