Moles 2

[Niha afzal]

What approach should I use in solvinh this question. Phosphorous mass dividedby total mass multiplied by 100 isnt giving me the ans.. im clueless even dnt know how to begin . Kindly givee me a slight hint

[hypervalent_iodine]

You've got the first part towards the answer, but you have to consider the rest of the question. It has stated that the mass percentage of P2O2 in a fertiliser is 30% and the question has asked you, with this information, what would the mass % of only phosphorus be in the fertiliser. You have calculated the mass % of P in P2O2, which is good, but you then need to carry that number on to work out the % in the fertiliser as a whole.

[Sensei]

You've got the first part towards the answer, but you have to consider the rest of the question. It has stated that the mass percentage of P2O2 in a fertiliser is 30% and the question has asked you, with this information, what would the mass % of only phosphorus be in the fertiliser. You have calculated the mass % of P in P2O2, which is good, but you then need to carry that number on to work out the % in the fertiliser as a whole.

On his photo I see P₂O₅, not P₂O₂.

 

Niha afzal, do you realize there is rotate option in the Paint and even Windows image viewer.. Rotate it 90 degree, the next time, so we will have easier to read your papers. Thank you.

 

What approach should I use in solvinh this question. Phosphorous mass dividedby total mass multiplied by 100 isnt giving me the ans.. im clueless even dnt know how to begin . Kindly givee me a slight hint

Mass of molecule is approximately sum of masses of each element in molecule.

Mole of P has ~31 g/mol

Mole of O has ~16 g/mol

So 31*2+16*5=~ 142 g/mol for whole P₂O₅

Percentage/fraction of P in P₂O₅ is 31*2/142=0.43 (43%) (you used 42.6, as far as I can see on the photo. It should be 43.64)

This is what would be if 100% of fertilizer would be P₂O₅. But you have just 30%.

So you have to multiply 0.4364 by 0.3 = ~0.131

Edited March 24, 2016 by Sensei

[hypervalent_iodine]

On his photo I see P₂O₅, not P₂O₂.Niha afzal, do you realize there is rotate option in the Paint and even Windows image viewer.. Rotate it 90 degree, the next time, so we will have easier to read your papers. Thank you.

Yes, thank you for spotting it. I was writing from a new phone and kept making the same typo without realising it.

[StringJunky]

Yes, thank you for spotting it. I was writing from a new phone and kept making the same typo without realising it.

I made the same error..

[Niha afzal]

Thanku guys thanku so much. Yes stringjunky il make sure to rotate them next time.