Using Materials

1. What is "corrosion" ?

Answer: Corrosion is the destruction of materials by chemical reactions with substances in the environment.

2. What metals make up bronze?

Answer: Bronze is made of copper and tin.

3. Which metal alloy has a low density?

Answer: Aluminium alloys have low density.

4. What is a "thermosoftening polymer" ?

Answer: A polymer that softens and melts when heated.

5. What is borosilicate glass made from?

Answer: Borosilicate glass is made from sand and boron trioxide.

6. Iron is an important metal in the construction industry. It is often used in the form of steel to reinforce structures and make them stronger.

a) Define the term "alloy".

Answer: Alloys are a mixture of a metal with small amounts of other metals or carbon.

b) Compare the properties of high carbon and low carbon steels.

Answer: High carbon steel is strong but brittle. Low carbon steel is softer and more easily shaped.

c) Steel, like iron, can corrode. Name the type of corrosion found on steel.

Answer: rusting

d) Write a word equation for rusting.

Answer: iron + water + oxygen  →  rust

7. The figure below shows three test tubes that were used to investigate rusting.

a) Explain the purpose of adding anhydrous calcium chloride to test tube 1.

Answer: Anhydrous calcium chloride is a drying agent that removes any water from the test tube.

b) Explain the purpose of oil in test tube 2.

Answer: Boiled water has no dissolved air (oxygen) in it. The oil floats on the surface of the water and stops any other air from dissolving back into the water.

c) Explain why test tube 3 is the only one which shows evidence of rusting.

Answer: For rusting to happen there needs to be iron, oxygen and water. Test tube 3 is the only test tube with all the reactants needed for rusting.

d) Suggest three ways that the results from this experiment could be made more reliable.

Answer: Repeat the experiment. Compare the results with other groups who did the same experiment. To see if similar results were collected.

e) Suggest how this experiment on rusting could be improved to obtain quantitative results.

Answer: The mass of the iron nail could be taken at the start of the experiment. Then the mass of the iron measured at the end of the experiment (remove the rust) and measure the iron at the end of the experiment. Then calculate the % mass change to allow direct comparison between the conditions without any error from initial mass differences for each nail.

8. The table below shows the composition of gold used in jewellery.

a) Write down the missing values, A and B.

Answer: A = 0 and B = 58.5

b) Explain why 24 carat gold is desined as pure.

Answer: Pure means containing only one type of substance. 24 carat gold contains only gold atoms and so is pure.

c) List the names of the metals used to alloy with gold.

Answer: Gold is usually alloyed with silver, copper and zinc.

d) A ring was made of 2.5 g of metals. Calculate how much more gold would be in a 24 carat ring compared to a 18 carat gold ring.

Answer: 24 carat gold ring would have 2.5 g of gold. 18 carat gold ring would have 1.875 g gold. Therefore, there is 2.5 - 1.875 = 0.625 g more gold in the 24 carat ring than the 18 carat ring.

e) Alloys of gold can be used in dental fillings. Justify the use of gold in dental fillings.

Answer: Gold is an unreactive metal and therefore will not chemically react with the body or food and drinks. This means that it is long lasting and durable. As pure gold is so soft, it must be turned into an alloy to make it strong and wear resistant as teeth will wear away pure gold. Gold alloys will have a lower melting point than gold and can be easily cast into any shape to make a bespoke filling and is easier to put into position in the mouth.

9. Glass is a type of ceramic material made of mainly silicon dioxide.

a) Name the main raw material used to make glass.

Answer: Sand is the raw material used to make glass.

b) Describe how soda-lime glass is made.

Answer: Soda-lime glass is made by heating a mixture of sand, sodium carbonate and limestone.

c) Give one difference of borosilicate glass over soda-lime glass.

Answer: Borosilicate glass melts at a higher temperature than soda-lime glass.

d) A contact lens is a prescription medical device that can rest on the surface of the eyeball and improve a person’s sight. Glass or polymers can be used to make a contact lens. Evaluate the use of contact lenses and the material used to make them.

Answer: Contact lens must be transparent and bend the light. Both glass and some colourless polymers can do this. Glass is more expensive than plastic. Glass is more brittle than plastic and therefore more likely to break and be less comfortable to wear. Therefore, polymers are a better choice of material to make contact lens.

e) Modern contact lenses are a mixture of polymers, which include thermosoftening polycarbonates. Explain the difference between thermosoftening and thermosetting polymers. Include a labelled diagram in your answer.

Answer: In thermosoftening polymers chains are not joined to each other, but they are tangled up. This means they soften and melt when heated. In thermosetting polymers, chains are joined together by covalent bonds known as crosslinks. This means they do not soften or melt when heated.

10. Composite materials are made from two or more materials.

a) Give an example of a synthetic composite and describe its structure.

Answer: Fibre glass with the matrix or binder made from a polymer and the reinforcement or fragments made from glass fibres. Concrete with the matrix or binder made from a cement and water and the reinforcement or fragments made from sand and crushed rock. Composite wood with the matrix or binder made from adhesives and the reinforcement or fragments made from wood fibres. Carbon fibre composites with the matrix or binder made from a polymer and the reinforcement or fragments made from carbon fibres and carbon nanotubes.

b) Justify natural wood being classified as a composite.

Answer: Natural wood is made from more than one material. It is made from a matrix (lignin) with fragments (cellulose fibres) in it.