Determination Of Formulae

Question 1

What are molecules?

Answer 1

Compounds containing two or more atoms held together by covalent bonds.

Question 2

What is the molecular formula?

Answer 2

This is the number of atoms of each element in a molecule.

Question 3

What is meant by empirical formula?

Answer 3

This is the simplest whole number ratio of a atoms of each element in a compound.

Question 4

What is the empirical formula important for?

Answer 4

Substances that do not exist as molecules:
Metals
Some non-metals
Ionic compounds

Question 5

What do substances that do not exist as molecules form?

Answer 5

Giant crystalline structures of atoms or ions.

Question 6

What does this abbreviation mean: Mr?

Answer 6

Relative molecular mass

Question 7

What is meant by relative molecular mass?

Answer 7

This compares the mass of a molecule to the mass of an atom of carbon-12.

Question 8

How do you calculate the relative molecular mass?

Answer 8

Add together the relative atomic masses of the elements in the compound.

Question 9

What is the relative formula mass?

Answer 9

This compares the mass of a formula unit with the mass of an atom of carbon-12.

Question 10

How do you calculate the relative formula mass?

Answer 10

Add together the realise atomic masses of the elements in the empirical formula.

Question 11

What is the process of investigating the chemical composition of a substance called?

Answer 11

Analysis

Question 12

What is a hydrated salt?

Answer 12

This is where water molecules are a part of the salt’s crystalline structure.

Question 13

What is the water of crystallisation?

Answer 13

Water molecules that are bonded into a crystalline structure of a compound

Question 14

What is meant by the term anhydrous?

Answer 14

Dehydrated

Question 15

What happens to the crystalline structure without water?

Answer 15

The crystalline structure is lost.

Question 16

What are the two assumptions made when finding the water of crystallisation through an experiment?

Answer 16

All of the water has been lost.

There is no further decompositio.

Question 17

Why is it difficult to see whether all of the water in a hydrated salt has been removed?

Answer 17

The colour of the substance may have changed but water may be present inside the crystals.

Question 18

How do you make sure that all of the water has been removed from a hydrated salt?

Answer 18

Reheat until there is no longer a mass change.

Question 19

Why is it difficult to judge if the salt has a further decomposition?

Answer 19

It’s difficult to judge if there’s no colour change so a different product could be formed if heated for too long.