Video: GCSE Chemistry Foundation Tier Pack 1 • Paper 2 • Question 3

GCSE Chemistry Foundation Tier Pack 1 • Paper 2 • Question 3

05:29

Video Transcript

Brass is an alloy of copper and zinc. The ratio of copper and zinc in brass can vary. Figure 1 shows the composition of a type of brass called “low brass.” High brass contains a higher proportion of zinc than low brass does. A typical sample of high brass has 35 percent zinc. Draw on figure 1 to show the percentages of copper and zinc in high brass.

Let’s start off by having a look at figure 1. Figure 1 is a stacked bar graph. The percentage of each material is indicated by the height of its respective bar. So for instance, in law brass, we have this much copper and this much zinc. Here we’re using the key to work out which metal corresponds to which bar.

We already know from the question that high brass contains more zinc than low brass does. Therefore, we expect the bar to do with zinc in high brass to be bigger than that in low brass. And we expect the bar to do with copper to be smaller.

Remember that all the percentages must add up to 100 percent. So we can work out the percentage of copper in high brass by taking 35 percent away from 100 percent. This is equal to 65 percent. Now, we can draw on figure 1 the bar for copper. There we are, the bar for copper rises from zero percent at the bottom up to 65 percent.

It’s better to start with copper than with zinc because in low brass copper is indicated first. However, if you did start with the zinc and put the copper on top, that would be fine, as long as you’ve labelled them.

The width of your bar does not really matter. However, I’ve drawn it to have a similar width as the bar for low brass. If you draw it wider or thinner, that’s okay. The last thing to do with the copper bar is label it. Here, I’ve used the symbol for copper Cu.

Now, we can move on to the bar for zinc. There, I’ve drawn in the zinc bar so that it covers 35 percent’s worth of the 𝑦-axis. And the last step is to label it zinc as I’ve done here using the symbol for zinc, Zn.

Alternatively, to match the key, you can shade in the copper bar more strongly than the zinc bar. So there we have it. We’ve drawn on figure 1 to show the percentages of copper and zinc in high brass: 65 percent copper and 35 percent zinc.

What is the percentage of zinc in low brass?

Again, let’s have a look at figure 1. We’ll use the key to identify the bars as copper and zinc and then we read off the 𝑦-axis to work out the percentage of zinc. Now, here’s a question: is the percentage of zinc 100 percent, 80 percent, or something else? Well, it’s the height of the bar of zinc that indicates its percentage not the value of the percentage of the top or the bottom.

So the calculation we need to do is to work out the difference between a percentage at the top of the bar and the percentage of the bottom of the bar. This is 100 percent minus 80 percent. This is equal to 20 percent. So the percentage of zinc in low brass is 20 percent.

High brass is used to make springs, which were originally formed from wire. State two properties that high brass needs in order for it to be a good material for making springs.

Let’s consider for a moment the properties of a spring. A spring has to be strong. A load is applied and it needs to be able to resist that load. A spring also needs to be relatively stiff so that it doesn’t deform too much when a load is applied. And you wouldn’t want a spring to rust or corrode. So you would want a material that makes up the spring to be corrosion resistant.

But there’s one more necessary property of high brass in order for it to be useful for making springs. And that’s its ability to be formed into a wire.

So what’s the key word which means that a material can be easily drawn into a wire? That word is ductile.

Now since the question mentioned that springs are made from wire and that material made into a wire has to be ductile, I’m putting ductile as my first answer. And I’ve selected strong as my second answer. However, any two of these four options would be acceptable.

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