4.4 Gravimetric analysis

Question 1

What does the tare function do?

Answer 1

It resets the balances display value to zero

Question 2

What is a weighing boat for?

Answer 2

Weighing

Question 3

How do you weigh by difference?

Answer 3

1) weigh the weighing boat
2) record the mass
3) remove the weighing boat and add the substance being weighed
4) re-weigh the weighing boat

Question 4

What does the term “weigh accurately approximately” mean?

Answer 4

weigh as close as possible to a certain mass but ensure that you record the actual mass given on the balance

Question 5

How would you heat to a constant mass?

Answer 5

1) heating a substance
2) allowing to cool in a dedicator to prevent absorption of water
3) weighing
4) repeating the steps of heating, cooling and weighing until no further changes in mass are observed

Question 6

What is gravimetric analysis used for?

Answer 6

to determine the mass of an element or compound in a substance

Question 7

What happens during gravimetric analysis?

Answer 7

• the substance is converted into another substance of known chemical composition, which can be readily isolated and purified

Question 8

What are the two types of conversion in gravimetric analysis?

Answer 8

• precipitation
• volatilisation

Question 9

What happens in a precipitation conversion?

Answer 9

• the substance undergoes a precipitation reaction
• the precipitate is separated from the filtrate and the filtrate tested to ensure the reaction has gone to completion
• the precipitate is washed, dried to constant mass then weighed

Question 10

what happens in a volatilisation conversion?

Answer 10

• the substance is heated and any volatile products (often water) are evaporated
• the substance is heated to a constant mass and the final mass recorded