National Chemistry

1. Calculate the percentage of carbon in propane.

That is, the amount of C in C3H8

This will be a fraction multiplied by 100 to get a percentage

  carbon  x 100
  propane

  3 x C  x 100
  C3H8

Then into mass:   1 mole of C3H8 = (3 x C) + (8 x H)

  = (3 x 12) + (8 x 1)

 
  = 42g

Calculation  36  x 100 = 85.7%
  42

2. Calculate the percentage of nitrogen in ammonium nitrate.

That is, the amount of N in NH4NO3

This will be a fraction multiplied by 100 to get a percentage

    nitrogen   x 100
  ammonium nitrate

Beware, there are 2 nitrogens in ammonium nitrate

   2 x N   x 100
  NH4NO3

Then into mass:   1 mole of NH4NO3 = (2 x N) + (4 x H) + (3 x O)

  = (2 x 14) + (4 x 1) + ( 3 x 16

 
  = 80g

Calculation   2 x 14   x 100 = 28  x 100 = 35%
  80 80

Find Percentage composition calculations in the following papers
2001 Q13(c)(ii) 2002 Q12(b) 2003q15(c) 2004 Q 17(c)
2005 Q11(b) 2006 Q11(b) 2007 Q17(c) 2008 Q16(a)
 

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