Gravimetric Analysis

Question 1

What should be done when adding to the weigh boat

Answer 1

When adding to the weigh boat remove it from the balance. This prevents spillage onto the balance which will affect your weighing accuracy

Question 2

What is the first method of weighing by difference

Answer 2

1. Mass of empty weigh boat
   - now add approximate mass of substance you need
2. Mass of weighing boat and substance (A)
   - tip substance into where you want it
3. Reweighing empty boat plus residue (B)
4. Mass of substance used A-B

Question 3

What is the second method of weighing by difference

Answer 3

1. Put a weigh boat on balance and zero
   - now add a,out of substance required
2. Mass of weigh boat and substance X
   -tip substance into where you want it
3. Reweigh empty boat and residue Y
4. Mass of substance used X-Y

Question 4

Weighing accurately approximately

Answer 4

Get an accurate value close to the required amount but ensure you record the the actual mass given on the balance

Question 5

What does heating to constant mass ensure

Answer 5

Heating to constant mass ensures that all the water has been removed

Question 6

What must the sample be cooled in

Answer 6

The sample must be cooled in a desiccator so no moisture can be reabsorbed as the silica (chemical in the base) in the desiccator keeps the atmosphere dry

Question 7

Which step is essential when drying a precipitate in gravimetric analysis

Answer 7

repeating the steps of heating, cooling and weighing until no further changes in
mass are observed

Question 8

What is gravimetric analysis used for

Answer 8

Gravimetric analysis is used to determine the mass of an element or compound in a substance

Question 9

What is the substance converted into

Answer 9

The substance is converted into another substance of known chemical composition, which can readily be isolated or purified, this conversion can occur either through precipitation or volatilisation

Question 10

What happens in the precipitation conversion

Answer 10

In precipitation conversion 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 and then weighed.

Question 11

What happens in volatilisation conversion

Answer 11

In volatilisation conversion the substance is heated and any volatile products (often water) are evaporated. The substance is heated to constant mass and the final mass recorded.