3.2 Determination of formulae

Question 1

Define molecular formula

Answer 1

actual number of atoms of each element in a molecule

Question 2

Define empirical formula

Answer 2

simplest whole number ratio of atoms of each element present in a compound

Question 3

What is the anagram for calculating empirical formula from masses

Answer 3

E
M
M
A
R

Question 4

What do each each of the letters in the anagram for empirical formula stand for?

Answer 4

E - element
M - mass
M - Mr
A- answer (moles)
R - ratio

Question 5

Method of heating hydrated salts to work out its formula

Answer 5

1. weigh crucible without and with sample of salt
2. heat the crucible for 5 mins then weight again
3. repeat heating and weighing until concordant results
4. work out moles of water and moles of anhydrous salt
5. find smallest whole number ratio to work out the formula

Question 6

What does a dot in the middle of a compound mean?

Answer 6

Bonded in some way
e.g. water from crystallisation in hydrous salts

Question 7

What happens to many salts after heating?

Answer 7

The colourful salts often lose their colour