How many kilograms of a fertilizer are made of pure P2O5 would be required to supply 1.69 kilogram of phosphorus to the soil?

3.89 kg P2O5 must be used to supply 1.69 kg Phosphorus to the soil.

Explanation:

The molecular mass of P2O5 is

P2 = 2 * 31 = 62

O5 = 5 * 16 = 80

Molecular Mass = 142

Set up a Proportion

142 grams P2O5 supplies 62 grams of phosphorus

x kg P2O5 supplies 1.69 kg of phosphorus

Though this might be a bit anti intuitive, you don't have to convert the units for this question. The ratio is all that is important.

142/x = 62/1.69 Cross multiply

142 * 1.69 = 62x combine the left

239.98 = 62x Divide by 62

239.98/62 = x

3.89 kg of P2O5 must be used.