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What is the percentage by mass of phosphorus in the fertiliser? AS level MCQ

  1. Apr 8, 2012 #1
    1. The problem statement, all variables and given/known data
    A garden fertiliser is said to have a phosphorus content of 30.0% ‘P
    soluble in water’.
    What is the percentage by mass of phosphorus in the fertiliser?
    A 6.55% B 13.1 % C 26.2% D 30.0%

    2. Relevant equations

    3. The attempt at a solution

    I got the percentage by mass of P in P2O5, which was 68/148 X 100 which was 45.9%
  2. jcsd
  3. Apr 8, 2012 #2
    Good start. Now, there is 30% by weight phosphorus pentoxide in the fertiliser in total...
  4. Apr 8, 2012 #3
    Code (Text):
    KK so can you just see if I am right? Lets say the compund is P2O5X. Out of the compund P2O5 is 30%. Now out of this 30% P is 45.9%. So amount of P is 45.9/100 X 30%?
  5. Apr 9, 2012 #4


    User Avatar

    Staff: Mentor

    Not bad, the only problem being - there is no 45.9% P in P2O5. Close, but different number.
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