CHAPTER 4 CHEMICAL CALCULATIONS

Question 1

How do you calculate the relative formula mass

Answer 1

By adding all the relative atomic masses of the elements of a compound in the ratio showed by it’s formula

Question 2

What’s a mole

Answer 2

One mole of any substance is it’s relative formula mass im grams

Question 3

What does the number of moles =

Answer 3

Mass(g) / Ar
Or
Mass(g) / Mr

Question 4

What is avagadros constant per mole

Answer 4

6.02 x 10^23

Question 5

How to find perecntage of mass

Answer 5

Use Ar then Mr then divide that over total for example
Percentage of Of mass of CO2
Is 12(2x16)=44
32/44x100 = 72.7%

Question 6

How to do reacting mass calculation and example

Answer 6

What mass if oxygen reacts with 12 g of magnesium
2Mg + O2 —> 2MgO
Tick the one you know (magnesium) and question mark above you’re trying to find (oxygen)
Then do moles magnesium = mass/Mr 12/24 = 0.5
Then moles O2 = 0.25 because of scale factor of 2 from the magnesium
Then mass O2 =Mr x moles 32x0.25 = 8g

Question 7

How to find molar ratio(finding reacting ratios) explanation and example

Answer 7

140g of nitrogen (N2) reacts with 30g of hydrogen (H2) to form ammonia
Moles of N2= 140/28 = 5mol
Moles of H2 = 30/2 = 15mol
Ratio:5:15
1:3

Question 8

How to calculate concentrations

Answer 8

Condentration (g/dm^3) = amount of solute (g) / volume of solution (dm^3)

If working in cm^3 times by 1000 on outside if equation