# AQA Chemical Calculations (C2 - Higher)

Hope these help, stick it on your wall or put it in a folder,

you are welcome to distribute sheets around schools etc.

- Created by: Chris Smith
- Created on: 21-11-09 15:01

First 223 words of the document:

Chris Smith Year 11 Bourne Grammar School

Chemical Calculation Revision Sheet (assuming you can workout

relative mass and know what Ar and Mr are)

Empirical formula:

Q: Suppose 3.2g of sulphur reacts with oxygen to produce 6.4g of sulphur oxide.

What is the formula of the oxide?

step action S O

1 find masses 3.2 3.2

2 look up given Ar values 32 16

3 divide masses by Ar 0.1 0.2

4 find the ratio 1 2

Use the fact that the Ar of sulphur is 32 and the Ar of oxygen is 16.

Result= SO2

Atom Economy:

(Mass of desired products / mass of all) x 100

Percentage yield:

(Actual mass obtained/ Maximum obtainable mass) x 100

Mole (mol)

Mass (in g) / Mr (of element or compound).

Moles in a solution

Volume in litres x moles per litre of solution.

E.g. How many moles in 185cm3 of a 2mol solution = 0.185 x 2 = 0.37 mol

Percentage Mass

(Ar x No. of atoms (of the element) / Mr (of whole compound)) x 100

E.g. find percentage mass of sodium in sodium carbonate (Na2CO3)?

Ar of sodium= 23, Ar of carbon=12, Ar of oxygen=16

Mr of Na2CO3= (2x23) + 12 + (3x16) = 106

So if we substitute these into the equation it gives us:

(23x2)/ 106 all times by 100 = 43.4%.

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