MEMORANDUM OF ASSESSMENT Module 3: Materials

Transcription

1 1. During the preparation of concrete, cement is mixed with sand. a. Which other components are needed to make concrete? b. Name the raw materials needed to make cement. c. Describe how to go about to produce concrete which is hard and strong. d. Compare bricks in its compressive strength and tensile strength which make it suitable for building houses. a. gravel and water b. limestone and clay c. Keep the concrete moist to prevent it from drying too quickly. Make sure that the ratio of cement in the mixture is not too small. d. Bricks need to have a good compressive strength because it should not break with a lot of pressure from above. Bricks do not need a good tensile strength as it will not be stretched or bend. 2. Glass is always part of the contents of domestic rubbish. a. Glass is often used to make containers for food keeping. Suggest two reasons why glass is suitable for this. b. Waste glass poses a problem to the environment. State possible problems that can be caused by waste glass. c. Discuss possible ways of minimising waste glass. a. Glass is not poisonous. It is transparent which makes the food easily identifiable. b. Waste glass makes the environment unsightly. Broken glass can cause cuts. Warm stagnant water can be trapped in the glass and become the breeding ground for mosquitoes which can lead to diseases such as malaria. c. Re-cycling of glass bottles. Use carton containers instead of glass bottles like for milk and juices. 3. There are many objects that we use in our daily life that are made of different types of plastic. a. Name any two types of plastic and one use for each. b. Though plastics are such useful materials, their use also poses problems to us and to our environment. Mention two problems associated with the use of plastics. c. Suggest possible ways of reducing the problems you mentioned in (b) above. a. Melamine for making table tops. Polythene for making shopping bags. Polyurethane for making foam mattresses. b. Plastics are non-biodegradable and flammable. Animals can choke when it gets swallowed. When burnt the plastics give off poisonous fumes. Plastic clog the drains and sewage systems. c. Reduce the use of plastic products to force a reduction in its production. Use paper bags instead of polythene for shopping. Reuse plastic containers wherever you can. Choose recyclable packaging materials such as glass and cardboard.

2 4. The following diagrams show the structures of nylon, cellulose and polythene. a. All three substances are formed by polymer molecules. Explain the meaning of a polymer. b. Compare the strength of the polymer molecules for these three substances. c. Cellulose can be crushed into thin fibres. (i) What are these fibres usually used for? (ii) Glucose, a carbohydrate, is the building unit (monomer) of cellulose. Which three elements are found in cellulose? d. State one use of polythene. a. A polymer is a long chain formed by carbon atoms joining together by covalent bonds. b. Nylon polymers are the strongest, compared to cellulose and polythene. The polymers of cellulose are strong and those of polythene weak. c. (i) For making paper. (ii) carbon, hydrogen and oxygen d. For making shopping bags. 5. Learners investigated the heat conductivity for different materials, P, Q, R, S and T. It was done by filling a metal tank with hot water which had five small holes in it to put in the different materials. Candle wax was attached to the tips of the materials as shown in the diagram below. The materials were equal in length. The table below shows the results of the investigation. Material P Q R S T Time for wax to melt (seconds) a. Why is it important that the materials should all have the same length? b. Use the information to determine which material would be a good insulator. c. Two of the materials are metals. Suggest which two are they.

3 a. Heat conductivity is influenced by the length of a material. The longer a material the longer it takes for heat to be transferred through it. b. T. It takes very long to conduct heat through it. c. Q and R 6. Brass and bronze are alloys which are used for making ornaments. a. Explain the meaning of alloys. b. Which metal is common in both brass and bronze? c. Which alloy from brass or bronze also contains zinc? d. Zinc is also used for galvanizing iron plates. Explain what is meant by galvanizing and state the use for the galvanized iron plates. a. Mixture of different metals or a metal and another substance. b. Copper c. Brass d. Galvanizing is coating iron with zinc metal to prevent it from rusting. It is used for making roofs. 7. Aluminium is extracted by electrolysis as shown in the diagram. a. (i) Name the common ore of aluminium. (ii) Describe how the aluminium ore is purified before the aluminium is extracted by electrolysis. b. Name the chemical products formed at the (i) positive electrode (ii) negative electrode c. Suggest a reason why the products produced during electrolysis are kept separate. d. Aluminium and copper can both be extracted by electrolysis. State why reduction with carbon in a furnace is preferred for copper. e. Aluminium is used in overhead electricity cables. State one other use of aluminium. a. (i) bauxite (ii) The ore is first dissolved in cryolite and then heated for the ore to melt. b. (i) oxygen (ii) aluminium c. Aluminium is very reactive and can easily binds with the oxygen again. d. Electrolysis needs electricity which is very expensive. It is cheaper to burn the copper ore with carbon in a furnace. e. Used for making aircraft parts.

4 8. The bar chart shows the percentage composition of different types of steel A, B, C and D. a. From the bar graph: (i) State the common element in all types of steel. (ii) Identify stainless steel. (iii) State the percentage composition (%) in stainless steel. (iv) Explain the difference in the composition of mild and hard steel. b. The table shows the properties of and uses for the different types of steel. Write down the information for (i), (ii) and (iii) in the above table. Name Property Use hard steel (i) razor blades mild steel easily worked (ii) stainless steel tough and does not (iii) corrode tungsten steel tough and hard also at high speed cutting tools high temperatures c. From the table choose the suitable steel for electric drill bits. Give a reason for your choice. a. (i) iron (ii) D (iii) iron 74%, chromium 18%, nickel 8% (iv) Hard steel has a higher percentage of carbon than mild steel. b. (i) tough and brittle (ii) car bodies (iii) cutlery c. Tungsten steel. Drill bits need to be hard and tough and be able to work at high temperatures.

5 9. a. How do the ions formed by metals compare to those formed by non-metals? b. With reference to the metallic bond, explain why (i) metals conduct heat (ii) metals are ductile. a. Metal atoms lose its valence electrons to form positive ions (cations). Non-metals gain electrons to form negative ions (anions). b. (i) When the metal is heated, the electrons closest to the point that is being heated move faster. They bump into the electrons next to them causing them to move faster and so on, until all the electrons are moving at the same speed. (ii) The metal atoms are arranged in layers which can move across each other when a force is applied. 10. a. Name the main ores of: (i) aluminium (ii) copper (iii) iron b. The iron produced in the blast furnace contains up to 4% carbon and is very brittle. Explain how the carbon content can be reduced. a. (i) bauxite (ii) copper pyrites (iii) haematite b. Blowing more oxygen (hot air) in the blast furnace. 11. a. What is meant by the term alloy? b. What elements make up the following alloys? (i) duralumin (ii) solder (iii) mild steel c. Suggest a reason for the difference in properties between a pure metal and its alloy. d. How does the addition of carbon to iron affect its properties? e. Why, although iron rusts easily, does stainless steel not rust? a. A mixture of two or more elements where one should be at least a metal. b. (i) aluminium and copper (ii) lead and tin (iii) iron and carbon c. The different particle size can cause a disruption in the order of the arrangement of the particles. d. More carbon makes the metal more hard and brittle. e. Stainless steel contains chromium which forms a thin layer over the material.

6 12. aluminium calcium copper iron lead magnesium potassium zinc Choosing your answers only from the list of metals above, select: a. The metal which is lowest in the reactivity series. b. Two transition metals. c. A metal which forms an amphoteric oxide. d. Two metals which can form ions with a 3+ charge. e. A metal, compounds of which cause atmospheric pollution. a. copper b. copper and iron (also lead and zinc) c. aluminium d. aluminium and iron e. lead 13. The diagram shows a traditional house. a. Name the material used for building the wall. b. Give one i. advantage of the materials used for making the roof. ii. disadvantage of the materials used for making the roof. c. Corrugated iron can also be used for making roofs. Suggest one reason why corrugated iron is suitable for roofs. a. Wood b. (i) Cool in summer and hot in the winter. (ii) Can easily catch fire and be worn off. c. Durable against wearing off. Strong and do not rust easily. Waterproof and fire proof.

7 14. The diagram below shows part of a building. a. The walls of the building are insulated with polyurethane (plastic foam). Describe how this method keeps the temperature more or less constant inside the building. b. Cement is one of the components of concrete. (i) Name the raw materials used to manufacture cement. (ii) State what happens to concrete when it sets hard. c. Tensile strength is a physical property of bricks. State what is meant by tensile strength. d. Thatch, rather than corrugated iron, is used for roofing in rural areas due to its availability. Outline an experiment how to test which material is best for roofing. e. The table compares some properties of glass and ceramic (fired clay). Complete the table by writing down the missing information. property material glass ceramic type of chemical bond (i) ionic molecular arrangement random (ii) relative bond strength moderate strong f. Use the in (e), the table above, and deduce the melting point of ceramic from the relative bond strength. a. Polyurethane is a poor conductor of heat. b. (i) limestone and clay c. The tensile strength of a material is the ability of the material to allow for its bending or stretching. d. Build three small identical model houses but different roofing materials, example metal, ceramic and thatch. Put the three model houses in the sun and measure the temperature in each of them every 5 minutes. Record the results in a table and draw graphs of temperature against time to compare the three materials. e. (i) ionic

8 (ii) orderly f. Very high melting point e.g. 1600ºC. MEMORANDUM OF ASSESSMENT 15. Fibres are made into fabrics which are used to make clothing. This is a list of four fibres: wool, polyester, cotton, nylon. a. What do all fibres have in common with respect to their molecular structure? b. Choose from the given list : i. one natural fibre ii. one synthetic fibre c. The clothing manufacture has to decide which fibres have the quality that will be best for the clothes. Why wool is often used to make winter clothing? a. All are polymer molecules. b. (i) wool or cotton (ii) nylon or polyester c. Wool traps air which makes it a good insulator. It therefore keeps the heat inside. 16. Maria investigated the insulating properties of three materials, cotton, polyester and wool. She used a stop-clock, a copper can with lid and thermometer. She started the experiment with boiling hot water and allowed it to cool for 30 minutes and recorded the temperature every 5 minutes. Temperature (ºC) Time (minutes) Cotton Polyester Wool Un-wrapped a. (i) Give the role of the un-wrapped copper can. (ii) Suggest one way how the investigation can be improved. b. From the results in the table give the temperature: (i) at which the experiment started

9 (ii) to which the water in the un-wrapped can cooled to (iii) change for the greatest drop of wrapped cans. c. Based on the results, suggest with a reason the best material for covering a warm water bottle. a. (i) It is the control to ensure fair testing. (ii) Repeat the experiment a few times and use the average values. b. (i) 98ºC (ii) 31ºC (iii) = 62ºC c. Wool because it shows the lowest drop in temperature. 17. Learners investigated the absorbance and drying of fabrics R,S and T. They tabulate their findings as follows: R S T Original dry fabric mass (g) Remaining amount of water after wet fabric removed (g) Wet mass of fabric (g) R S T Time to dry (minutes Time to dry on a windy day (minutes) a. Explain why the same dry mass was used for all three the fabrics. b. Identify from the table the fabric, R, S or T that (i) absorbed the least water (ii) dried the fastest without wind. c. Write the letter of the fabric, R, R or T, suitable for the making of towels. Give a reason for your choice. a. The absorbance of water is been tested and therefore no water should at the start of the experiment. The fabrics must therefore be dry. b. (i) R (ii) R c. T. The towel should absorb water easily but should not take too long to dry.