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

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SUMMARY

The discussion focuses on calculating the percentage by mass of phosphorus in a fertilizer containing 30.0% phosphorus pentoxide (P2O5). The correct calculation involves determining the mass percentage of phosphorus (P) in P2O5, which is 45.9%. However, since the fertilizer contains 30% P2O5, the final percentage by mass of phosphorus in the fertilizer is calculated as 45.9% of 30%, resulting in a value of 13.1%. The correct answer is option B, 13.1%.

PREREQUISITES
  • Understanding of chemical formulas, specifically P2O5.
  • Basic knowledge of percentage calculations.
  • Familiarity with mass percentage concepts in chemistry.
  • Ability to perform unit conversions and dimensional analysis.
NEXT STEPS
  • Study the composition and properties of phosphorus pentoxide (P2O5).
  • Learn how to calculate mass percentages in chemical compounds.
  • Explore the significance of phosphorus in fertilizers and its impact on plant growth.
  • Review common chemical equations and their applications in agricultural chemistry.
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Students preparing for AS level chemistry exams, educators teaching chemical calculations, and individuals interested in understanding fertilizer composition and its implications for agriculture.

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Homework Statement


A garden fertiliser is said to have a phosphorus content of 30.0% ‘P
2
O5
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%


Homework Equations





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%
 
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Good start. Now, there is 30% by weight phosphorus pentoxide in the fertiliser in total...
 
Code:
sjb-2812 said:
Good start. Now, there is 30% by weight phosphorus pentoxide in the fertiliser in total...

KK so can you just see if I am right? Let's 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%?
 
Not bad, the only problem being - there is no 45.9% P in P2O5. Close, but different number.
 

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