Empirical And Molecular Formulas

Question 1

Empirical formula

Answer 1

Gives the smallest whole number ratio of atoms in a compound

Question 2

Molecular formula

Answer 2

Gives the actual number of atoms in a molecule

Question 3

What is the molecular formula made up of

Answer 3

A whole number of empirical units

Question 4

A molecule has an empirical formula of C4H3O2, and a molecular mass of 166, work out its molecular formula

Answer 4

Find the relative mass, =83
Then do the molecular mass / relative mass
=2 empirical units in the molecule
Molecular formula must be the empirical formula x 2
=C8H6O4

Question 5

How can empirical formulas be calculated

Answer 5

Through experiments
First work out how many moles of the products you have

Question 6

Empirical formula can be worked out by…

Answer 6

Percentages of different elements using n=mass/M

Question 7

Percentage composition

Answer 7

(Total madd of element in compound/total mass of compound) x 100

Question 8

Can molecular formula also be calculated by experiments

Answer 8

Yes

Question 9

Water of crystallisation

Answer 9

Some compounds have water molecules incorporated into them, known as water of crystallisation

Question 10

Hydrated compounds

Answer 10

Contain water

Question 11

Anhydrous compounds

Answer 11

Don’t contain water

Question 12

What is the ration of moles of hydrated compound to moles of water of crystallisation

Answer 12

1 mole will always have the same number of moles

Question 13

Can percentage yield ever be 100%

Answer 13

No

Question 14

Percentage yield

Answer 14

(Actual yield/theoretical yield) x 100