﻿Hello, and welcome to your next lesson of the using resources topic. Today's lesson is all about alloys. Please make sure that you have a pen and a piece of paper ready, and that your phone is on silent and at one side so that you don't get distracted. So once you're ready, let's go. So what we're going to do today is start off by looking at why metals are alloyed. We will then move on and look at examples of different alloys and their uses before looking at some exam style questions where we're going to interpret and evaluate the composition and uses, of the alloys when we are given some information and we will finish the lesson off with a quiz. So it's a recap of the structure of metals and metallic bonding. So this picture that we've got here shows a diagram of metallic bonding. So we have the dark orange circles. These are showing positive metal ions. They are positively charged because they have lost electrons. And then we have the sorts of light yellow circles, and they are delocalised electrons. Remember electrons have a negative charge. Now it's important noting that this diagram, the positive metal ions are quite far apart. That is not the case in metallic bonding. The positive metal ions will be really close together. Now metals form a giant metallic structure. So again, the diagram is showing just a snippet of what would be a very large structure. Now, what happens as you can see is that the positive metal ions are regularly arranged. They form layers. So the positive metal ions are arranged in closely packed layers. Now these layers are able to slide over one another. And so in an example, we're going to look at today, pure iron is relatively soft and easily bent and shaped because of these positive metal ions, which are able to slide over each other because of the regular arrangement of ions that form. So why are metals alloyed? So what we can see here is a structure of a metal alloy. Now, an alloy is when you have a mixture of metal atoms with atoms of a different element. Now, normally that atoms of a different element are normally a metal. Now, hopefully from the picture, you can see that this is different in structure to When we just have one metal, and it forms the lovely regular arrangement of layers, what happens is because we have atoms of a different element, these atoms are likely to be different in size. And therefore what happens is the regular arrangement of the ions are disrupted. So we don't have the nice, neat layers that you get when you have just a pure metal. And it's for this reason, because the metal ion layers have been disrupted that the alloys are much harder than the pure metal, because the layers of the metal ions can no longer easily slide over one another. So this is going back to just looking at a pure metal and just showing that the rows of the metal ions are able to easily slide if a force is applied. So for example, if you put a hammer to a pure piece of metal, what essentially happens is that the layers of metal ions are able to move and slide. Now remember that the metal is not going to break. The reason for it is because we still have the sea of delocalised electrons, which are negatively charged and obviously the positive metal ions. And we have got something called electrostatic attraction between the positive metal ions and the negatively charged sea of delocalised electronics. And so what happens is that the sea of delocalised electrons are able to keep the giant metallic lattice in shape as the rows slide. So we're just going to do a series of quick fire questions. I'll read the question you need to select which one is correct. So what charge do metal ions have? Well done if you selected positive. Metal ions are positively charged. Surrounding the positive metal ions is a sea of delocalised protons. Well done if you selected false. Surrounding the positive metal ions is a sea of delocalised electrons. Alloys are much softer than pure metal. Well done if you selected false. Alloys are much harder than pure metal because remember the layers, the regular arrangement of the layers has been disrupted due to different size atoms now in the structure. So what you are going to do now is you are going to pause the video and I would like you to answer the following questions on your piece of paper. Once you have answered all the questions, if you can please press play, and then we can go through the answers. So please pause the video now. Okay. So let's go through the answers. Please make sure that you pause the video now and you correct any answers you didn't get right. And you obviously mark correct the ones that you did. Please press play once you have marked your work. Okay. So an alloy remember is when you have a mixture of metal and potentially a nonmetal, but quite often it's when you have a mix of two metals. So an example of an alloy, which you've probably heard of is bronze. Now bronze is an alloy and it has many different uses, but one of them being statutes. Okay. Another example of an alloy is brass. So both bronze and brass contain copper. Copper is a metal. And brass, one of the uses of brass is in a musical instruments. And then another example of an alloy is stainless steel and a common use of stainless steel is in cutlery. So what we've got here is a table, and we're going to look at five different alloys, composition just means what it's made up of. We're going to look at the properties that these alloys have and some of their uses. So bronze is made up of copper and tin. Now a useful property of bronze is that it's resistant to corrosion, hence why it's used in statues because statues are quite often outside, and so they're exposed to really harsh weather conditions. And therefore it's a positive thing that they're not going to cover it over time. Bronze is also used for decorative items or it's avoiding the household and is also used for ship propellers. Brass is also made up of copper. But this time it is mixed with zinc. Now brass is very hard, but it's workable. And some examples are musical instruments, taps and door fittings. So obviously it's really important for those three that the alloy is very hard. You don't want it to be soft or ability to change shape. We then have high carbon steel. so we have iron with one to 2% carbon. So what happens is the addition of carbon, which is a non-metal, it disrupts the layers of ion. So therefore it makes steel much harder than pure ion. So high carbon steel is strong, but it's brittle. And it's used for things like cutting tools and metal presses. We then have low carbon steel. So they says iron with carbon, but this time it contains less carbon, hence it's called low carbon steel. So it contains less than 1% carbon. And in low carbon steel, because there's a lot less carbon. That means that the layers of iron ions are less distorted and less disrupted. And therefore they're more easily able to slide over each other. And hence low carbon steel is soft and it is easy to shape. And low carbon steel is used extensively in manufacturing, such as in making cars, machinery and ships. And then the final example of an alloy that we're looking at is stainless steel. And again, we have got iron because remember steel always contains iron. And this time the iron is with chromium and nickel and the properties of stainless steel is that it's resistant to corrosion and it's hard. And use of stainless steel is in cutlery and in plumbing. And if you think in both of those cases, cutlery and plumbing, they are going to be frequently exposed to water. Remember rusting which applies to iron. One of the things needed for rusting to take place is water. So it's really important because the iron is mixed with chromium and nickel it's resistant to corrosion. You don't want your cutlery or your plumbing being corroded by the water that they're exposed to. So again, a series of quick fire questions to you, check what we've just done. So bronze is used to make musical instruments. Well done if you selected false. It is brass that is used to make musical instruments. Brass and bronze both contain copper. Well done if you selected true. They do both contain copper. Bronze is resistant to corrosion. Well done if you select a true. Remember one of the uses of bronze is in statues. Steel always has iron in. well done if you selected true. Steel will always have iron in. Stainless steel is used to make cutlery. Well done if you selected true. So what's going to happen now is a series of questions are going to come up. I would like you to pause the video now and using your piece of paper and pen, I would like you to write the answers down. Once you have finished answering the questions, if you can please click play so that we can mark your answers. So please pause the video now. Okay. So going through the answers. The answers are on the slides now. If you can please pause the video. If you can please mark your work. Make sure you correct any answers you didn't get right And then if you can press play once you are finished. So what we're going to look at now is as an exam style question. So what this looks like in an exam, so we're going to look at interpreting some data on different alloys. So brass is an alloy of copper and zinc. The table below shows the percentage by mass of copper and zinc in two types. So we've got red brass, which is made up of 85% copper and 15% zinc. And then we have yellow brass, which is made up of 60% copper and an unknown mass of Zinc. So the first question, calculate value X in the table. So how we're going to do this is we are looking at percentage by mass. Now a percentage will always equal a hundred percent. when you know that yellow brass is made up of 60% copper. So it's work out the percentage by mass of zinc for yellow brass, all we're going to do is a hundred, which is the percentage we would end up with. So a hundred take away 60, and that will give us our value. So a hundred take away 60 gives us 40. So the percentage by mass of zinc in the yellow bras is 40%. Next question is, explain why red brass is softer than yellow bras. Use the table and your own knowledge. Okay. So what we're going to do is look at how much copper, red brass and yellow brass contain. So red brass has 85% copper. Whereas yellow brass only has 60% copper. If we look at how much zinc each one contains, red brass contains 15% zinc, yellow brass contains 40% zinc. So how you would write that as an answer is that red brass contains more copper and therefore the layers slide more easily because in this case, it's how much zinc is in alloy. The more zinc there is the more the layers will be disrupted, the harder it will be for the layers to slide. And why is yellow brass more suitable than red brass for making door keys? Now door keys obviously need to be hard. You don't want them to be soft and you definitely don't want them to change shape. So again it's all to do with how much copper and how much zinc that is in yellow brass. So yellow brass contains less copper and more zinc than red brass. And so it's less likely to be able to bend. So yellow bras has a higher percentage of zinc, so 40% compared to 15%. And so it is less likely to bend. So what you're going to do now is have a go yourself. So carbon steel is an alloy of iron and carbon. The table below shows the percentage by mass of iron and carbon in two types. So we've got high carbon steel and we have low carbon steel. First thing that you need to do is calculate value X in the table. Then I would like you to explain why low carbon steel is softer and easier to shape than high carbon steel. And you need to use the table and your own knowledge. And then which still would be most useful for making tools like chisels? And why? So if you can please pause the video now and have it go at answering those questions. And once you are finished, if you can please press play and we will mark your work. So going through the answers. So first thing you have to do was calculate the value of X. So you should have done a hundred takeaway 98 gives you an answer of 2%. And then if you can pause the video, a mark question two and three, please make sure anything you didn't get to you write it. Okay. So a recap of what we have learned today. So pure metals are softer than alloys due to the regular arrangement of metal ions and the ability of the layers to slide over each other. Alloys are a mixture of metal atoms with atoms of a different elements. I remember quite often, this different element is actually another metal. Alloys are harder than pure metals due to the disruption of the layer arrangement. So well done on all your fantastic work this lesson. Please make sure that you now click next to complete the quiz.

This lesson will look at metals and why they are often alloyed. We will look at common examples of alloys and what they are used for.

Chemistry

Y11 Chemistry

Key Stage 4

Year 11

Alloys

Using Resources

UNIT

Finite resources

Life cycle assessments

The importance of recycling

Phytomining and bioleaching

Rusting

Polymers

Glass, ceramics and composites

Water safe to drink

Required practical on potable water

Wastewater treatment

Making ammonia and the Haber Process

The economics of the Haber Process

Making fertilisers in the lab and in industry

Review lesson

Review lesson: Chemistry content

Exam skills: Compare and evaluate

Case study: Kitty Hach Darrow

Lesson overview: Alloys

Video

Presentation

Worksheet

Exit Quiz

Transcript

18 lessons in Using Resources: