Lesson 1 — Activity 2: Classifying Matter



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Scientists use different ways to identify and classify matter. One of the ways is to determine physical and chemical properties.

Another way is to once again use the particle theory of matter. Scientists use the particle theory to organize substances into two basic categories based on how many types of particles they contain.


 

Classifying Matter

 

You will learn about how matter can be classified in this activity.



Physical and Chemical Properties

Think about how you would describe a friend. You might refer to the person’s height, weight, and eye or hair colour. These are physical characteristics or properties.


 When speaking about matter, physical properties include things like size, colour, smell, melting point, and boiling point.

If you were asked to describe a friend’s character or the way your friend interacts with other people, you would be talking about qualities that are similar to chemical properties.


 A chemical property tells how a substance will react with other substances. An example of a chemical property is how easily a substance catches fire.


The table below lists some physical and chemical properties of matter.




Self-Check


Try This!

Try the questions below on your own first and then click on the tab to check your answers!

1. List at least three physical properties of matter.


2. What is a chemical property?



1. Physical properties may include shape, colour, smell, melting, boiling, or freezing points, or if matter is magnetic or flexible.

2. A chemical property tells how a substance will react with other substances.





 

Matter can also be classified into categories based on how many types of particles they contain. The two basic categories are pure substances and mixtures.

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A pure substance is a single substance not mixed with anything else. It is made up of only one type of particle. Examples of pure substances include distilled water, sugar, and baking soda.


Sugar


Baking Soda



A mixture has two or more particles or items that do not react chemically when put together. In some mixtures, you can see the different types of substances because similar particles stay clumped together.

 Pizza is an example of a simple mixture. It is made of bread and can contain tomato sauce, pepperoni, mushrooms, and cheese — or whatever toppings you like! You can see each of the items or toppings and can pick them apart if you don't like mushrooms! When the ingredients are put together, they make up a delicious meal!



Mixtures can be either homogeneous or heterogeneous:

A homogeneous mixture, sometimes called a solution, is relatively uniform in composition; every portion of the mixture is like every other portion.

For example, if you dissolve sugar in water and mix it really well, your mixture is basically the same no matter where you sample it.



A heterogeneous mixture, sometimes called a mechanical mixture, is a mixture whose composition varies from position to position within the sample.

For example, if you put some sugar in a jar, add some sand, and then give the jar a couple of shakes, your mixture doesn’t have the same composition throughout the jar. Because the sand is heavier, there’s probably more sand at the bottom of the jar and more sugar at the top.

(You will learn more about homogeneous and heterogeneous mixtures in upcoming lessons.)



Differences between Pure Substances and Mixtures

If you looked at two clear, colourless liquids and were told that one was a pure substance and the other was a mixture, could you tell which was which just by looking at them? Probably not.

In order to tell the substances apart, you would have to examine more of
their properties. You might be able to tell them apart by colour, smell, or texture. You might need to look at their chemical properties. Or you might have to investigate their boiling and freezing points.

Mixtures boil and freeze at different temperatures than the pure substances that make them up. In our part of the world, temperatures are low enough in winter for snow and ice to form. This can make driving and walking dangerous as roads and sidewalks become slippery. Road crews use this property of mixtures to keep roads clear of ice. The interaction of salt and ice is an interesting thing to explore.

 
Oregon Department of Transportation, CC BY 2.0


Salt lowers the freezing/melting point of water, so in both cases, the idea is to take advantage of the lower melting point. Ice forms when the temperature of water reaches 0 degrees Celsius (32 degrees Fahrenheit). When you add salt, that temperature drops: A 10-percent salt solution freezes at –6° C (20° F) and a 20-percent solution freezes at –16° C (2° F). On a roadway, this means that if you sprinkle salt on the ice, you can melt it. The salt dissolves into the liquid water in the ice and lowers its freezing point.


 

Experiment!

Materials Required:

ice cubes

2 glasses

table salt

teaspoon

tablespoon

stirring rod

thermometer


Put two ice cubes in two glasses. Put a teaspoon of table salt on one ice cube.

1. Which ice cube melts faster: the one with the salt or the one without the salt?

 2. Why does this happen?

1. The ice cube without salt melts slower because the air around it is warmer than 0 degree C (32 degrees F). The salted cube melts faster.

2. When you add salt it dissolves into the water of the ice cube. Salt water freezes at a lower temperature than the 0 degrees C (32 degrees F) at which freshwater freezes. The difference between the air temperature and the freezing point of salt water is bigger than the difference between the air temperature and the freezing point of freshwater. This makes the ice with salt on it melt faster.





Now try putting ice in a glass of cold water. Leave it there for 10 minutes or so. What temperature is the water? Recheck the temperature every few minutes. Does it get any colder?

Next, add a tablespoon of table salt to the water. Stir the ice, salt, and water together. Does the temperature change? Keep stirring. What temperature can you get it to be?


Here's what happened. The salt dissolves in the water. Fresh water freezes at 0 degrees C (32 degrees F). Salt water freezes at lower temperatures, depending on how much salt is in the water. As the ice turns to water, the change from solid to liquid requires heat. This is just like when water changes from liquid to gas; for example, when evaporating sweat cools your skin. As ice melts, the heat is taken from the ice and water around it. Both get colder. How cold can you get the ice, water, and salt? When the Fahrenheit temperature scale was first made, 0 degrees F was the lowest temperature that could be made using salt, water, and ice.