Lesson Video: Uses of Metals Chemistry • 7th Grade

In this video, we will learn how to identify the uses of metals, such as copper, aluminum, and steel, based on their physical and chemical properties.


Video Transcript

In this video, we will learn about the metals we commonly use in everyday life and in industry and why they are suitable for the applications we use them in. The commonly used metals we’re going to look at are copper, aluminum, iron, steel, tin, lead, silver, and gold. You’ve probably come across all of these in your daily life. These are all pure metals except for steel, which is an alloy. However, copper, aluminum, iron, tin, lead, silver, and gold are usually used in alloys rather than in their pure form.

The metals and other elements in an alloy affect the properties of an alloy. For example, aluminum is low in density, and so aluminum alloys are lightweight and are therefore used in lightweight applications. So metals and their alloys have certain properties, and these properties directly determine the applications or uses of the metals and alloys.

Some of the more important properties to consider when choosing a metal or an alloy for a certain application are strength, malleability, corrosion resistance, and density. Besides these physical properties, cost is also an important factor to consider when choosing a metal or an alloy for a specific application. Now, let’s have a look at some of the more noticeable properties of each of the metals listed, as well as their common applications.

Let’s look at two metals at a time, and we’ll begin with copper and aluminum. Copper has a lovely pink-orange color when its surface is clean and aluminum a silver-white color. Silver white is a fairly common color for a fresh, clean metal surface. But pink orange is a fairly unique color, quite distinctive to copper. This property would help us identify copper or an alloy which contains a high amount of copper. Aluminum’s melting point is much lower than that of copper. It would melt and set much quicker than copper when molding metal parts.

Now copper is an excellent thermal and electrical conductor. We use it mostly in its pure form in electrical wires. Besides its conductivity, copper is also relatively cheap. Copper is also hard. And though it tarnishes to a green color over long periods of time, it doesn’t flake away like iron does when iron corrodes. And so copper is used in plumbing parts, as well as to strengthen gold and silver alloys. Some coins are made of copper.

For aluminum, we said that one of its distinguishing properties is its low density. Alloys used to make aircraft and bicycle bodies contain a high percentage of aluminum, and this makes these components lightweight. We also use aluminum in beverage cans, such as soda cans, in food packaging, and foils because this metal is corrosion resistant and lightweight. Some modern building construction parts, such as window frames and doors, are fabricated from aluminum. Again this is because of its corrosion resistance property.

Let’s move on to the next two metals. Iron is silver gray when its surfaces are cleaned and fresh with no corrosion, while steel, which contains iron and carbon, has a gray surface. The melting points of iron and steel are much higher than the other metals we are investigating in this video. Notice that the melting point for carbon steel is given in terms of a range. This is because the ratio of iron to carbon in the carbon steel alloys can be varied. Another video on steels goes into more depth on this.

Now, iron is used in more applications than any other metal, but mostly in steels. Pure iron rusts easily and is relatively soft, so pure iron is not very useful to us. But alloying iron in steel increases its strength and hardness, perfect for making machine parts. These undergo a lot of friction but have a long lifespan because of their strength and hardness. Car bodies, tools such as hammers and drill bits, and reinforcing bars for the construction industry are some of the common uses of steel alloys.

We said that the proportions of iron to carbon in carbon steel can be controlled and altered. The relative proportions of these elements determine the strength-to-brittleness ratio and thus the specific application of a specific carbon steel. In stainless steel, besides iron and carbon, there is also chromium and nickel. The presence of chromium and nickel in the alloy gives it corrosion resistance. We make cutlery and surgical equipment from stainless steels because of this property of corrosion resistance.

Let’s move on to tin and lead. A clean surface of tin has a silver color, while lead has a gray color. Both these metals have relatively low melting points compared to the other metals we are investigating in this video. The relatively low melting point of tin makes it melt quickly and easily but also cool and set quickly. And so we use it in solder. Tin has a low corrosion rate and doesn’t oxidize very easily. And so a thin layer of tin is sometimes used to coat steel to prevent the steel from corroding. Think of tin cans. Tin food cans are not made of pure tin but are only coated in a thin layer of tin. This prevents the steal from rusting and contaminating the food.

Now lead has a high density and is also corrosion resistant. For these reasons, it is sometimes used in the construction industry for roofing and gutters. However, lead is being phased out in some applications in certain countries because lead is hazardous to the environment. Lead has another interesting application in science and medicine. It is used as a shielding medium from radiation such as X-rays. It is the high density of lead which gives it this interesting application.

Let’s have a look at the last two metals, silver and gold. Silver, with its silver color, when untarnished and gold with its distinctive yellow gold color are both precious metals. This is because they both have a high luster, which means they are very shiny. They are rare and costly. Because of their property of a high luster as well as their desirability because of their cost and rarity, they are both used in jewelry. Now, gold is highly corrosion resistant, but silver does tarnish over time. Both these precious metals are highly malleable and conductive, but they are not commonly used in other applications because of their high cost.

For the various metals that we have looked at, we have mostly discussed their physical properties. However, corrosion resistance is a chemical property. Other chemical properties and chemical uses of these metals have not been discussed in this video. We have seen that a metal has specific properties, which determines its usefulness in specific applications. This flowchart can work backwards or from the middle. For example, if we know the properties of a specific metal, we can potentially identify the metal. Or if we have a desired application and we want to make something specific, we’d have to know the properties that suit that particular application. And from the properties, we could determine the metal or alloys which are suitable for that application. Let’s practice this a bit.

The table shows the properties of five different metals. (a) Which metal is most suitable for use in aircraft bodies? And the answer options are (A) metal a, (B) metal b, (C) metal c, (D) metal d, or (E) metal e.

The properties of different metals listed in the table are strength, malleability, corrosion resistance, and density. Cost is not really a property of a metal but is a factor that a company will consider when fabricating a specific metal part. The properties of metals determine how useful they are in different applications. Note that the pure form of a metal is often not used for applications. Usually metals are used in alloys. And the properties of the metals in the alloy determine the overall properties of the alloy.

The question asks which metal is most suitable for use in aircraft bodies. When making an aircraft body, a manufacturer would want to make it lightweight and relatively strong. These two factors of strength and density are arguably the two most important factors when making an aircraft body. Of the five given metals — a, b, c, d, and e — the one with the lowest density also has a moderate strength. These properties or characteristics would be useful for use in aircraft bodies. Metals a, b, c, and e have high, very high, or moderate density. They would not be suitable to make an aircraft body from because the body would not be lightweight. So the metal most suitable for use in aircraft bodies is metal d. Also, metal d is highly malleable and corrosion resistant. It can be molded into an aircraft body shape easily and would have a long lifespan.

(b) Which metal is most suitable for use in mass-produced gates and railings? And the answer options are the same as before.

When mass-producing a product, cost is often an important factor. In most cases but not always, a company will plan to produce a product at low cost but sell many units and thus make a good profit overall. When making gates and railings whose purpose is for security, strength is the most important factor, so strength and cost are arguably the most important considerations when mass-producing gates and railings. The most suitable metals from those in the table with a high strength and a low cost are metals a and b. Both could be suitable to make gates and railings.

To decide between the two, we’d need to know the relative cost of each, but we don’t have this information. b has a high strength, although not as high as a, and also has a high malleability. This means metal b will be easier to press into shape. This is particularly important if the gates and railings are made from flat panels pressed and cut into shape, making metal b cost less overall to make, compared to metal a which is less malleable. So the metal most suitable for mass-produced gates and railings is metal b.

Part (c) which metal is most suitable for use in hip replacements? And the answer options are the same as before.

What properties would an artificial hip joint need to have? Well, strength would be important to carry the weight of the body as well as corrosion resistance because the new hip joint would be constantly surrounded by bodily fluids as well as dissolved oxygen. Malleability is an undesirable property for a hip joint replacement. We would not want the weight of the body to deform or alter the shape of the hip joint replacement. So we’re looking for a metal with a high strength, a high corrosion resistance, and a low malleability. It would be really great if the cost of hip replacement were low. However, this type of replacement only occurs maybe once in the lifetime of a person. And so a high cost is not really an influencing factor here.

Metals a, b, and e all display high or very high strength. However, we can rule out metals a and b because they have a low corrosion resistance, while metal e has a very high corrosion resistance and a very high strength. Added to that, it has a low malleability. And although the cost is high, the part would have a long lifespan. So the metal most suitable for use in hip replacements is metal e.

Let’s summarize what we’ve learnt in this video. We compared some commonly used metals. Specifically, we compared some of the more noticeable properties of copper, aluminum, iron, steel, tin, lead, silver, and gold and listed some of the main uses or applications. We noted that these metals are usually not used in their pure form but mostly in alloys. And we know that steel is an alloy. We made a general observation that each metal has its own unique specific properties and that these properties directly determine and influence the applications of these metals.

We saw that this flowchart can also work backwards. If we know a specific application or design brief for a part that needs to be manufactured and understand the properties that it needs to have, we can then determine which metals are suitable and which are unsuitable to make that part from. Some of the most important properties to consider when choosing a metal are its strength, malleability, corrosion resistance, and density. We also briefly mentioned that cost, although it is not a property, is an important factor which influences whether a metal is chosen for use in a specific application or not.

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