Saturday, 30 March 2013

1.24 calculate empirical and molecular formulae from experimental data

Find the masses of the elements in the compound (by weight the compound then weighing it with elements taken out). Make these masses into percentages, divide each percentage by the ar of that element and you will have the number of atoms of it in a molecule.

e.g
Carbon= % mass 80, ar 12
C= 80/12= 6.7
Hydrogen= % mass 20, ar 1
H= 20/1= 20
C6.7H20

To find the empirical formula divide the molecular formula by the smallest number.

e.g
C6.7H20 /6.7
=CH3

12 comments:

  1. This comment has been removed by the author.

    ReplyDelete
  2. Replies
    1. It means crystallization:
      Element.xH20

      Delete
  3. This comment has been removed by the author.

    ReplyDelete
  4. This comment has been removed by the author.

    ReplyDelete
  5. i'm sorry if this is wrong but i think its like this:
    1)write mass/percentage of reactants
    2) divide mass of reactants by Relative Formula Mass
    3)divide the smallest number (to find ratio of atoms)
    4) write formula
    e.g 1)Sulphur = 3.2g (or 3.2%) and Oxygen = 6.4g (or 6.4%)
    2)S=3.2/32=0.1 and O=6.4/16=0.4
    3)S=0.1/0.1=1 and O=0.4/0.1=4
    4)SO4

    ReplyDelete
  6. The percentage isn't worked out just by looking at their masses @eve e.g 3.2g isn't necessarily 3.2% unless it is a substance which has a mass of 100g it is the mass of the substance you are working out divided by the total mass of the whole substance so in your case it is 3.2/3.2+6.4 × 100

    ReplyDelete
  7. The Chemistry Syllabus has changed…

    Here is a New blog for the 2017 Syllabus:

    https://igcse-chemistry-2017.blogspot.hk/

    ReplyDelete