U4-1-2 - Gravimetric Analysis

Question 1

Why is heating to constant mass typically used?

Answer 1

To remove moisture (e.g. from primary standards)

Question 2

Name this piece of equipment

Answer 2

Desiccator

Question 3

What is the purpose of a desiccator?

Answer 3

Prevents reabsorption of water

Question 4

The formula for a compound is BaCl₂·3H₂O.

What is meant by ·3H₂O?

Answer 4

The compound forms a complex with 3 water molecules

(molar ratio BaCl₂ : 3H₂O is 1:3)

Question 5

During gravimetric analysis, a precipitate is formed and collected by filtration.

What must be done to the filtrate before moving on and why?

Answer 5

Filtrate must be tested by adding more reactant.

This is to ensure that no more precipitate is formed.

Question 6

How should a reactant be chosen for gravimetric analysis by precipitation?

Answer 6

Must be soluble and form an insoluble precipitate when reacted with analyte

e.g. silver nitrate is used to analyse halide ion content

Question 7

When heating to constant mass:
* heat sample
* cool in desiccator
* weigh
* ____________.

Answer 7

When heating to constant mass:
* heat sample
* cool in desiccator
* weigh
* repeat until constant mass reached.

Question 8

When heating to constant mass:
* heat sample
* ____________
* weigh
* repeat until constant mass reached.

Answer 8

When heating to constant mass:
* heat sample
* cool in desiccator
* weigh
* repeat until constant mass reached.

Question 9

When heating to constant mass:
* ____________
* cool in desiccator
* weigh
* repeat until constant mass reached.

Answer 9

When heating to constant mass:
* heat sample
* cool in desiccator
* weigh
* repeat until constant mass reached.

Question 10

When heating to constant mass:
* heat sample
* cool in desiccator
* ____________
* repeat until constant mass reached.

Answer 10

When heating to constant mass:
* heat sample
* cool in desiccator
* weigh
* repeat until constant mass reached.