Module 1- Practicals

Question 1

What chemicals can be irritants, and what is the precaution to take for irritants?

Answer 1

Dilute acid and alkalis

Wear goggles

Question 2

What chemicals can be corrosive, and what is the precaution to take for this?

Answer 2

Stronger acids and alkalis

Wear goggles

Question 3

What precautions should be taken around flammable chemicals

Answer 3

Keep away from naked flames

Question 4

What precautions should be taken around toxic chemicals (3)

Answer 4

Wear gloves, avoid skin contact, wash hands after use

Question 5

What precautions should be taken around oxidising chemicals

Answer 5

Keep away from flammable materials

Question 6

What method is used for measuring mass loss in thermal decomposition reactions? Outline the key steps.

Answer 6

1) weigh an empty clean, dry crucible and lid,
2) add the thing you wish to decompose to crucible and weigh again,
3) heat strongly with a Bunsen for a couple minutes,
4) weigh the crucible and contents again,
5) continue to heat and reweigh until you reach a constant mass, to ensure the reaction is complete

Question 7

What method is used for measuring mass gain when reacting magnesium with oxygen? Outline key steps.

Answer 7

Heating in a crucible.
1) Weigh an empty, clean dry crucible and lid,
2) Add magnesium ribbon (that has been cleaned with emery paper) to the crucible and weigh again
3) Heat strongly with a Bunsen for a couple of minutes,
4) occasionally lift lid with tongs to allow in some oxygen but take care not to let magnesium oxide powder to escape,
5) allow to cool,
6) weigh the crucible and contents again,
7) heat the crucible and reweigh until you reach a constant mass, to ensure the reaction is complete.

Question 8

Why should you avoid using large amounts of the compound you’re decomposing

Answer 8

Because the reaction is likely to be incomplete

Question 9

Why does the crucible need to be dry when measuring mass loss in thermal decomposition

Answer 9

Because otherwise a wet crucible would give an inaccurate result. The mass loss would be too large as the water would be lost when heating

Question 10

Why should you avoid using too small samples when measuring changes in mass

Answer 10

Because the percentage uncertainty would be too high