Properties of Matter

Pre-Assessment Questions What is matter? Can you give an example of matter? Are mass and volume the same thing? What is density? These are for informal class discussion.

Matter – anything that takes up space and has mass

Which of these are matter? You Table Dog Pop Water Air Carbon dioxide Light I let the kids orally answer and we discuss each of these, emphasizing that each thing that is matter has mass and takes up space. Light is not matter, everything else on this slide is matter. The kids often want to say that air is not matter, but you can demonstrate that air is matter by blowing up 2 balloons and taping them to opposite ends of a meterstick. Then balance the meterstick on your finger and carefully pop one of the balloons – it’s best to try to let the air out slowly so the pieces of the balloon don’t break off. The meterstick should tilt with the filled balloon end down to show that air does have mass and of course it takes up space in the balloon, so it must be matter.

Everything in the universe is either MATTER or ENERGY.

Matter has physical properties. Physical properties – characteristics that can be used to identify and describe materials. Any property that can be observed or measured is a physical property. Examples include: color, shape, brittleness, density, length, width, height, mass, and volume.

Science uses the metric system to measure. This is a good time to put in a quick review of the metric system or introduce the SI.

Measuring Mass Mass is the amount of matter (number of atoms) in an object. Mass does NOT change unless you add or subtract matter. In this demonstration, how could I change the mass of the water? The demonstration is water in a beaker. To change the mass, I could pour some out or add more or drink some (but we never drink out of lab equipment, so we have a little discussion about that)

Measuring Volume Volume is the amount of space an object occupies. Solids and liquids have a definite volume – that means you can’t change it without adding or subtracting matter.

Gases can compress or expand to the size of their container, so their volume can change; it’s NOT definite. Watch the demonstration. Which type of matter can be squeezed into a smaller space? I use a balloon that is blown up about halfway and tied and a board (as in a piece of wood). I step on the board and ask the students if I am compressing the board. Then for dramatic effect I usually jump up and down on the board and ask if I am making the board smaller. Then I squeeze the balloon and ask if I am compressing the air in it. A pop bottle with a lid might also work instead of the balloon.

We measure the volume of liquids with a graduated cylinder. Graduated cylinders are made of glass and will break if dropped. Please be careful with them!! I do have some plastic graduated cylinders that I often insist they use for this lesson, but I point out that in a real chemistry lab the graduated cylinders are glass because glass does not react with as many chemicals as plastic does.

We measure volume of a regular solid by using math. To find the volume of a box you multiply length times width times height. V = l x w x h

Example: A box has a length of 10 cm, a width of 5 cm and a height of 2 cm. Find volume. V = l x w x h V = 10 cm x 5 cm x 2 cm V = 100 cm3 cm times cm times cm = cm3 Demonstrate this with a box and a ruler.

We find volume of an irregular solid using the submersion method: An example of an irregular solid is a rock. To find its volume: Put water into a container such as a graduated cylinder. Note how much water there is. Put the object in and the water rises. Note how much the water rose and that’s the volume. Demonstrate this If your objects are larger than the opening of the graduated cylinder, fill a beaker completely with water and then gently submerge the object into it and catch the water that spills out the spout in a graduated cylinder. The water in the graduated cylinder is the volume of your object. Doing this on the edge of a sink so the water is being caught over the sink works well. Also, any objects that float in water need to be submerged without including your finger in the volume.

Why does this work? Since volume is the amount of space an object takes up, when you put an object in water it displaces the water. This means that the water still takes up the same amount of space for itself plus the amount of the object, so the water rises the amount of the volume of the object. This concept is important!!

Okay, now that you understand mass and volume, let’s put them together.

Which weighs more – a pound of feathers or a pound of lead? Actually, they weigh the same. But which takes up more space? This is to try to illustrate the importance of density.

Density Density is a measure of how closely packed the atoms are in a substance. density = mass divided by volume d = m/v

An example: An object has a mass of 30 grams and a volume of 6 milliliters. What is its density? m= 30 g v= 6 ml d=m/v d= 30g/6ml d=5 g/ml