Calculations

Question 1

What is Avogadro’s Constant?

Answer 1

6.02 x 10^23

Question 2

What is an atom’s Ar?

Answer 2

Relative Atomic Mass (in comparison to Carbon)

Question 3

What is the Mr of a substance?

Answer 3

The Ars of all the elements within the compound (incl. how many of each atom)

Question 4

How do you work out mass from moles and Mr?

Answer 4

Mass = Mr x mole (equation can be changed around)

Question 5

Percentage mass

Answer 5

(element Ar / compound Mr) x 100

Question 6

Percentage yield

Answer 6

(actual amount of product / maximum amount of product) x 100

Question 7

Percentage atom economy

Answer 7

(Mr of wanted products / sum of Mr of all reactants) x 100

Question 8

Volume of gas at room temp

Answer 8

Volume = moles x 24

Question 9

Moles from concentration and volume

Answer 9

Moles = Concentration x Volume

Question 10

Mass of solute from concentration and volume of solvent

Answer 10

Mass of solute (g) = Concentration (g/dm^3) x Volume of solvent (dm^3)

Question 11

mol/dm^3 -> g/dm^3

Answer 11

Divide by Mr (multiply for opposite direction)

Question 12

cm^3 -> dm^3

Answer 12

Divide by 1000 (multiply for opposite direction

Question 13

Finding concentration from titration

Answer 13

1. Balance symbol equation (for ratio)
2. Use given concentration to find moles of that solution
3. Use ratio to calculate number of moles of unknown solution
4. Calculate concentration using rearranged ‘moles = concentration x volume’
5. Change units if necessary