C1.21a Properties of steel and alloy steels Pure iron is too soft to be useful as a building material. Steel is iron with small amounts of carbon added. Alloy steels are made by mixing iron or steel with other metals. Different steels have different properties and so are suitable for different uses. Type pure iron steel (low carbon) steel (high carbon) stainless steel titanium steel manganese steel
Properties
Relative cost
iron
soft and weak
low
iron + about 0.1% carbon iron + about 1% carbon iron + 18% chromium + 10% nickel iron + 0.5–2% titanium iron + 14% manganese
harder and stronger than iron but easily shaped
low
harder but more brittle than steel
low
hard and very resistant to corrosion
high
able to withstand very high temperatures
high
extremely hard
high
What it contains
1
Which of the metals or alloys listed in the table are alloy steels?
2
Use the information in the table to choose the best steel for each of the following uses. Give reasons for your answers. a Paper clips b Cutlery c Cooker top d Razor blades e ‘Points’ for railway lines (to guide trains from one track to another) f Engine parts that have to operate at very high temperatures.
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C1.21b Making an alloy Higher Name
Class
Date
In this experiment you are going to make an alloy of lead and compare it to pure lead.
Prediction Predict which will be harder – the metal lead or the alloy you make from the lead.
1
______________________________________________________________________________
Apparatus Bunsen burner pipe-clay triangle tray of dry casting sand
crucible tongs spatula
carbon powder tin tripod mat thermal protective gloves
lead
Health and safety ● ● ● ●
Wear eye protection Take care with hot apparatus and with hot metal Lead is toxic – do not breathe in the vapour from the experiment Wash your hands after handling lead
Method A Collect a tray of dry casting sand. Make an indent in the sand using your finger. B Take masses of 1 g of lead and 1 g of tin.
crucible
C Put the lead into the crucible.
pipe clay triangle
D Put the crucible on a pipe-clay triangle on a tripod on a mat.
tripod
E Heat the crucible until the lead melts. Put a spatula-full of carbon powder on top of the molten lead to stop it forming a skin. F
Add the tin to the molten lead and stir with the spatula until the tin has melted and the two metals are thoroughly mixed.
F
Put on heat-resistant gloves. Pick up the crucible with the tongs and pour the mixture into the indent in the sand. Take great care to not spill or splash any of the hot, molten mixture.
HEAT
G Leave the alloy to cool down for a few minutes. H Try scratching a piece of lead and alloy together. The one that does not scratch is the harder.
Recording your results 2
Record whether the lead or the alloy was harder.
Considering your results/conclusions 3
Explain why the lead or the alloy was harder.
© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
C1.21c Alloys of gold Jewellery made from pure gold is very soft. Gold jewellery is usually made from alloys, in which gold is mixed with other metals. Different alloys have different colours. The most common form of gold has a yellow colour, whereas white gold looks more like silver and rose gold has a rose pink appearance. The purity of the gold is measured in carats or by the fineness. Pure gold is 24 carats and has a fineness of 1000. The table shows some different alloys of gold used to make jewellery. Purity of gold
Colour
Fineness
% gold
% silver
% copper
24 carat
yellow
1000
100
22 carat
yellow
917
91.7
5.5
2.8
18 carat
yellow
750
75
16
9
18 carat
rose
750
75
4
21
18 carat
white
750
75
4
4
9 carat
yellow
375
37.5
10
45
9 carat
white
375
37.5
62.5
% zinc
% palladium
17 7.5
1
What is an alloy?
2
Why is gold jewellery usually made out of gold alloys and not pure gold?
3
Use the data in the table to explain why 18 carat gold can have different colours.
4
How do you think the price of 9 carat gold compares to 18 carat gold. Explain your answer.
5
A fineness of 750 means the proportion of gold is 750 parts gold per 1000 parts of alloy. a Show how to convert fineness into percentage of gold. b What is the percentage of gold in an gold alloy with fineness 999? c What is the percentage of gold in an gold alloy with fineness 990?
Extra challenge 6
Some jewellery is made from 14 carat gold. a What percentage of gold is in this alloy? b What is the fineness of this gold?
7
An alloy of gold contains 60% gold. a What is the carat of this gold? b What is the fineness of this gold?
Š Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.