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)