Chemistry 4.4

Question 1

Percentage yield

Answer 1

actual/theoretical x 100

Question 2

Molecular formula

Answer 2

RFM of substance / RFM of Empirical formula
then x the answer by the result of the formula

Question 3

Percentage composition

Answer 3

mass of x / RFM of compound

Question 4

Empirical formula

Answer 4

Make table of mass RFM moles ratio. Then find ratio in simplest form and apply to compound

Question 5

Water of crystallisation

Answer 5

Find mass of water and mass of salt (not the original one). Find moles of each by finding RFM and then use moles to find ratio. Ratio for water = x.

Question 6

Reacting mass ratios

Answer 6

Find moles of substance who’s mass is given. Put moles into ratio according to number in front of that substance in chemical equation. Compare to ratio of substance it is asking you to find. Find moles of that substance using ratio. Find mass of substance using mass = moles x RFM

Question 7

Limiting reagant

Answer 7

Choose one substance. Find moles of that substance then use ratio to compare the moles needed for other substance. Then find moles of other substance and see if it is higher or lower than moles needed. If higher it is in excess, if lower it is limiting.

Question 8

What if a percentage is given instead of a mass?

Answer 8

Use percentage as mass. E.g if 80% use 80g.

Question 9

Define empirical formula

Answer 9

The simplest whole number ratio of elements.