Topic 5 – Separate Chemistry I

Question 1

State what is meant by oxidation

Answer 1

gain of oxygen

Question 2

Painting iron objects prevents corrosion.
Explain why painting iron objects prevents corrosion

Answer 2

• paint provides a protective layer
• so it excludes air/oxygen/water

Question 3

Ways of preventing corrosion of iron objects

Answer 3

• sacrificial protection
• galvanising
• electroplating
• painting iron

Question 4

Explain why copper added to aluminium to form the alloy makes the alloy stronger than pure aluminium (2)

Answer 4

• aluminum and copper have different size atoms
• so this prevents the layers of metal atoms from sliding over one another

Question 5

Pure metals can be made more useful by converting them into alloys or by electroplating them. Explain what alloying & electroplating are and how they can make metals more useful (6 marks)

Answer 5

• alloy - a mixture of metals
• in a pure metal, all atoms are the same size —> layers of atoms can slide over eachother easily
• so a pure metal is malleable/soft

• alloys are stronger than pure metals
• because atoms of different sizes
• layers cannot slide
• alloys can be used in bridges

• electroplating - a corrosion resistant metal coating is added on top of the pure metal/alloy
• (corrosion resistant) metal coating does not react with oxygen in air therefore pure metal object doesn’t corrode.

Question 6

Explain why aluminium alloys are stronger than pure aluminum (3)

Answer 6

• alloys contain atoms of different sizes
• prevents layers from sliding over one another in alloy
• whereas in pure aluminium, atoms easily slide over each other

Question 7

Explain why covering iron tools with a thin layer of grease prevents rusting

Answer 7

• air/oxygen/water excluded
• needed for corrosion

Question 8

Both air/oxygen AND water is needed for….

Answer 8

rusting

Question 9

What happens to iron as rust forms?

Answer 9

iron is oxidised (gains oxygen)

Question 10

Advantages for electroplating metal objects

Answer 10

• improves appearance
• helps prevent corrosion

Question 11

State why metals are electroplated

Answer 11

• improve appearance
• more corrosion resistant

Question 12

Platinum acts as a catalyst.
State, in terms of position in periodic table, why you would expect platinum to act as a catalyst

Answer 12

Transition metal

Question 13

State why an iron nail will not rust in a test tube with water and oil present

Answer 13

• Oil prevents oxygen from entering
• both oxygen & water needed for iron to rust