In this video, we will learn how to describe matter, the various characteristics matter can exhibit, and the importance these have in applications.
Matter is all around us. Matter is anything that has mass and volume. Mass describes the amount of matter an object contains. Volume is how much space matter takes up. Different substances have different characteristics. These different characteristics help us to distinguish substances from one another. For example, at room temperature, iron metal is very hard. Striking a block of iron with a hammer has little effect on its shape. Butter is somewhat soft, and we may be able to change its shape by simply squeezing it with our hand. It does not take very much thermal energy to melt butter. But it would take a very large amount of thermal energy to melt iron metal. Iron and butter have very different melting points.
In fact, different substances generally have different melting points. Melting point is the temperature at which matter begins to change from the solid to the liquid state. The melting point of butter is much lower than the melting point of iron. The melting point of iron is so high that we could not measure it in the laboratory. But we could measure the melting point of ice. Ice ordinarily has a melting point of zero degrees Celsius. Let’s take a look at the steps we could take to determine the melting point of ice.
First, we need to make a cold water bath and place it on a tripod. Then, we put crushed ice in a beaker and lower the beaker into the water bath. We’ll need to clamp the beaker to a stand to keep it upright. We should place a thermometer into the ice. Next, we light a Bunsen burner under the tripod and use it to heat the water bath. As we heat the water, it gains thermal energy. Some of this thermal energy is transferred to the ice. This causes the temperature of the ice to increase. When the ice reaches zero degrees Celsius, it begins to change from a solid to a liquid. In other words, it melts and turns into liquid water.
The melting point of ice is pretty low. But some substances have very high melting points. If we heated each substance given in the table, ice would melt first and iron would melt last. Iron has the highest melting point, so it takes the most amount of thermal energy to melt it. Iron and copper are both metals. Metals tend to have high melting points. If we get a metal hot enough, it will begin to soften. But once the metal reaches its melting point, it will begin to turn into a liquid. When a metal is soft, we can change its shape using much less force. If a metal has melted, it is often called molten metal. Molten metals can be molded into new shapes by pouring them into molds and letting them cool.
Liquid metals can also be mixed with other substances to form alloys. An alloy is a mixture of a metal element and one or more other metal or nonmetal elements. Stainless steel is an alloy made by mixing together iron metal, a few other metals, and the nonmetal element carbon. Forming an alloy can make a metal more useful. Alloys are often stronger and resist corrosion better than pure metals.
Now, let’s discuss boiling point. The boiling point is the temperature at which matter begins to change from the liquid to the gas state. To determine the boiling point of liquid water, we would need to heat the water. The water will absorb thermal energy and its temperature will rise. Ordinarily, when water reaches 100 degrees Celsius, it begins to form steam. Steam is the gaseous form of water. So, typically, the boiling point of water is 100 degrees Celsius. This is the boiling point of water at sea level. The boiling point of a substance depends on air pressure. At an altitude of 2400 meters, the boiling point of water is only 92 degrees Celsius. Air pressure is lower at higher altitudes.
So, in general, the boiling point of water tends to be lower when pressure is lower and higher when pressure is higher. In a pressure cooker, the boiling point of water gets higher as the pressure builds up inside. This means foods that contain a lot of water can be cooked very quickly, since the water is boiling at a higher temperature.
Different substances tend to have different boiling points. When liquid crude oil is taken from the Earth, it contains many different components. These components have different boiling points. Before crude oil can be separated, it is first sent to a furnace. Inside the furnace, crude oil is heated until it boils and turns into a gas. This gas is then sent to a fractionating column. This is also called a distillation column. Inside the fractionating column, the different gases condense. This means they change from gases to liquids. The column is coolest at the top and hottest at the bottom. Each gas condenses when it reaches a height in the column that has a temperature equal to its boiling point.
For example, fuel oil condenses near the bottom of the column because it has a pretty high boiling point. Diesel oil, kerosene, and gasoline all have lower boiling points than fuel oil. So these gases condense higher up in the column.
Now, let’s discuss the characteristic hardness. Some materials, such as rubber or butter, are soft at room temperature. Other substances, such as metals, coal, and sulfur, are hard at room temperature. Metals soften at high temperatures before they melt. When metals get soft, they can be shaped into new objects. Coal and sulfur do not soften before they melt.
Electrical conductivity is another important characteristic of matter. Some materials are good conductors of electricity and others are not. Good conductors conduct a large electric current. Metals are generally good conductors of electricity. Metals like copper and silver are used to make electrical wires and electrical equipment. Some types of solutions are also good conductors of electricity. Some acidic solutions, alkali solutions, and salt solutions can conduct electricity.
Poor conductors of electricity do not conduct an electric current. They are often called insulators. Most gases are insulators. For example, oxygen gas does not conduct electricity. Some types of solutions are insulators too. A solution made from dissolving sugar in water will not conduct electricity, neither will a solution made of hydrogen chloride and benzene. Some solids are also insulators. These include sulfur and phosphorus.
Materials may also conduct thermal energy to different degrees. Most metals conduct thermal energy well. Cooking pots are often made with aluminum because it is a good conductor of thermal energy. This helps us to heat foods to cook them. Heating coils in appliances are made with nickel and chromium metals because of how well they conduct thermal energy. Some examples of materials that do not conduct thermal energy well are wood, plastic, and rubber. These materials are used to make the handles of cooking pots. Because they are poor conductors of thermal energy, we can move or lift the pot during cooking without burning our hands.
Substances also differ in reactivity. Let’s discuss the reactivity of metals. Some metals have high reactivity. This means that they can react with many substances. Some metals have low reactivity. These metals do not react with very many substances. The following diagram is called the chemical activity series. “Activity” is another word scientists use for reactivity. The most reactive metals are found at the top of the series. As we move down the series, the metals become less reactive. Sodium and potassium are highly reactive metals. They are so reactive that they react rapidly with oxygen gas in the air. Potassium metal has a silvery-white color. After a few minutes in air, the surface of potassium tarnishes and turns a darker color. This happens because the potassium is reacting with oxygen in the air.
Potassium and sodium react very quickly with oxygen. Aluminum, iron, and copper react more slowly with oxygen. It would take several days of exposure to air before they tarnished. Silver, gold, and platinum do not tend to react with very many substances, including oxygen. So, they do not tarnish as easily in air. These metals are often used in jewelry because they will stay shiny for a long time. Most metals are lustrous, which means that they look shiny and bright. But when the surface of a metal tarnishes, it loses the shininess.
When only the surface of a metal reacts with oxygen in the air, we call it tarnishing. But if the reaction affects more parts of the metal, we tend to call it corrosion. Corrosion occurs in moist or humid air. When iron corrodes, we say that it is rusting. Manufacturers try to protect reactive metals from corrosion. One way to do this is by encasing the metal with a less active metal like gold. The gold does not react with oxygen. So, it makes a barrier to protect the iron underneath from reacting with oxygen. Or they may paint the metal with nonmetallic materials. This also prevents oxygen from reacting with the iron underneath the paint. Or they may apply grease. Grease is used to protect parts inside machinery. It will not chip away when parts of the machine move.
Before we summarize our learning, let’s take a look at a couple of questions.
In order to shape copper, the metal must first be heated to a temperature between 400 degrees Celsius and 700 degrees Celsius. Why must the metal be heated first? (A) To purify the metal, (B) to increase its luster, (C) to help harden the metal, (D) to help soften the metal, (E) to turn the metal into a gas.
Copper is a metal. Like many other metals, copper is a hard solid at room temperature. It would be extremely difficult to change the shape of a solid piece of copper, unless it was a thin sheet or wire. Copper has a very high melting point. The melting point of copper is 1085 degrees Celsius. We are told that to change the shape of copper, it must be heated to between 400 and 700 degrees Celsius. These temperatures are below the melting point of copper. When we heat copper, we are adding thermal energy to the copper. When the copper reaches a temperature between 400 and 700 degrees Celsius, it softens. But it does not melt, because we have not reached the melting point.
Soft copper is easier to bend, shape, and cut. So it can be made into many different useful products, such as cooking pots, jewelry, or sheets for the siding and decoration of buildings. Now we can see that the correct answer to the question is answer choice (D). Copper metal is heated before it can be shaped to help soften the metal.
Why are cooking pots and pans made from aluminum and not from plastic? (A) Aluminum is a better electrical conductor than plastic. (B) Aluminum is a better conductor of thermal energy than plastic. (C) Aluminum is light, whereas plastic is heavy. (D) Aluminum is easier to shape than plastic. (E) Aluminum is cheaper to produce than plastic.
The materials used to make pots and pans must be safe for humans and effective for cooking food. Aluminum is a metal. Like many metals, aluminum is stable at high temperatures. The melting point of aluminum is much higher than temperatures used to cook food. So, aluminum will remain a hard solid while cooking. Aluminum is also a good conductor of thermal energy. During heating, thermal energy moves into the aluminum in the pan. The aluminum quickly conducts some of this thermal energy into the food. This thermal energy raises the temperature of the food and helps it cook.
The handles of many pots and pans are made of plastic. Plastic is a poor conductor of thermal energy. So the handle will remain cool enough to hold while we are cooking.
Now, when looking at the answer choices, we can select choice (B) as the correct answer. Cooking pots and pans are made from aluminum and not from plastic because aluminum is a better conductor of thermal energy than plastic.
Now let’s summarize our learning with some key points. Matter is anything that has mass and volume. A material begins to change from solid to liquid at its melting point. A material begins to change from liquid to gas at its boiling point. Metals tend to soften before they melt and can be shaped or mixed with other substances to make alloys.
Metals are also generally good conductors of thermal energy and electricity. Some metals tarnish quickly in the air or corrode easily. These metals tend to react quickly with oxygen. Because of this, manufacturers protect highly reactive metals by coating them with less active metals, paint, or grease. Besides metals, some solutions containing acids, alkalis, or salts are good conductors of electricity. Most gases and a sugar solution are examples of poor electrical conductors.
Wood and plastic are poor conductors of thermal energy. Poor conductors of thermal energy are often called insulators.