Relative Formula Mass

Question 1

How do you work out the relative atomic mass of an element?

Answer 1

It’s just the mass number of the element.

Question 2

How do you work out the relative formula mass of a compound?

Answer 2

Add up all the relative atomic masses of the elements in the compound.

Question 3

All relative atomic masses are compared with the mass of which element?

Answer 3

Carbon-12

Question 4

One mole of a substance is equal to what?

Answer 4

The relative atomic or formula mass of the substance in grams.

Question 5

How do you find out the number of moles in a substance?

Answer 5

Mr of element or compound

Question 6

How do you calculate the percentage of a SPECIFIC element in a compound?

Answer 6

Ar x No. of Atoms of Specific Element
——————————————————- x 100
Mr of the whole compound

Question 7

How do you calculate the Empirical Formula of a compound?

Answer 7

List the elements in the compound.
Divide each element by its Ar.
Multiply the result of step 2 of each element by 10.
Simplify to the simplest ratio.

Question 8

How do you work out the percentage yield of a reaction?

Answer 8

Actual Yield (Grams)
  -----------------------------      x 100
Predicted Yield (Grams)

Question 9

Yields are always ____ than 100%

Answer 9

Less than

Question 10

Give reasons why you never get 100% yield.

Answer 10

• If the reaction is reversible, the reaction goes both ways, so some of the products are always reacting together to return to the original reactants.
• Things burn and are lost as smoke