C4: Chemical calculations

Question 1

What is the Law of Conservation of Mass

Answer 1

Atoms cannot be created or destroyed

Question 2

Why is that

Answer 2

Total mass of reactants is the total mass of products

Question 3

How do we calculate the relative atomic mass of an atom

Answer 3

Find the atomic mass of the compound

Question 4

How do we balance a chemical equation

Answer 4

Before and after a reaction, there must be the same number of atoms of each element

Question 5

Is this balanced?
H2 + 02 = H20

Answer 5

That is unbalanced as although the hydrogen is fine, we need one more oxygen

Question 6

Is this balanced?
H2 + 02 = 2H20

Answer 6

This balances the oxygen, however we would have too much hydrogen atoms. So that is still unbalanced

Question 7

Is this balanced?
2H2 + 02 = 2H20

Answer 7

Yes that is as there are 4 hydrogens and 2 oxygens on both sides

Question 8

What is the molecular formula

Answer 8

The actual amount of atoms making up a molecule
Eg: C6H1206. This is glucose

Question 9

What is the empirical formula

Answer 9

The simplest ratio of atoms that make up a molecule
CH20

Question 10

What is a mole

Answer 10

A mole is a measure of chemical amounts

Question 11

What is the Avogadro Constnant

Answer 11

Shows that 1 mole of a substance is 6.02 X 1023 atoms of that substance

Question 12

How do we calculate relative formula mass of a substance

Answer 12

It is equal to the mass of 1 mole of the substance. This is the same as relative atomic mass for an element

Question 13

Prove this

Answer 13

The mass of 1 carbon mole is 12g, which is the same ass the atomic mass of carbon

Question 14

Calculate the relative formula mass of carbon dioxide C02

Answer 14

1. Work out the AR of Carbon
   12
2. Work out the AR of one oxygen
   16

12 + (16 x 2) = 44

Question 15

How do we calculate moles

Answer 15

Mass divided by Relative Formula Mass

Question 16

What is a limiting reactant

Answer 16

When it is completely used up when reaction stops when used up

Question 17

What should we ensure when neutralising an acid

Answer 17

Theres no leftover acid after the reaction

Question 18

How can we solve this

Answer 18

Use an excess amount of the other reactant

Question 19

What is excess

Answer 19

more than neccessary

Question 20

What is the other equation for moles and what are the measurements

Answer 20

Concentration X Volume

Moles = mol
Volume = dm cubed
Concentration = mol/dm cubed

Question 21

How do we calculate percentage yield

Answer 21

(real yield/theoretical yield) x 100

Question 22

How do we calculate atom economy

Answer 22

(relative molecular mass of desired products/total relative molecular mass of all reactants) x 100