Chemical formulae, equations and calculations

Question 1

Mole

Answer 1

The unit for amount of substance

Question 2

Mass

Answer 2

Number of mols*mass of 1 mol

Question 3

Empirical formula

Answer 3

Gives the simplest whole-number ratio of atoms present in a compound. It can be worked out from experimental data

Question 4

Molecular formula

Answer 4

Gives the actual number of each type of atom present in a molecule (covalent compound) or formula unit (ionic compound)

Question 5

Percentage yield

Answer 5

Actual yield/Theoretical yield x 100%

Question 6

Molar volume of gas (at room temperature and pressure (rtp))

Answer 6

24dm³ or 24000cm³

Question 7

How to find the formula of metal oxide by combustion?

Answer 7

1. Weigh a crucible with lid
2. Place a piece of metal ribbon about 10cm long in the crucible and weigh them
3. Set up the apparatus
4. Heat the crucible strongly (roaring flame)
5. Lift the lid every few seconds
6. When the reaction is finished allow the crucible and contents to cool
7. Weigh them

Question 8

Why is a lid used?

Answer 8

To prevent metal oxide powder from escaping

Question 9

Why must the lid be lifted?

Answer 9

To allow for more oxygen to react

Question 10

How to find the formula of a metal oxide by reduction?

Answer 10

1. Weigh a ceramic dish
2. Put about 3g of metal oxide on the dish and weigh it
3. Set up the apparatus
4. Pass hydrogen gas over the metal oxide
5. Ignite the excess hydrogen
6. Heat the metal oxide
7. Allow the dish to cool then weigh it