Chapter 8 Density

Density Density describes the amount of mass in a given volume of a substance. In other words, density describes how closely packed together the particles are in a material.

Density A substance with a lower density will float on substances with higher densities.

The size of a material does not affect density. A big piece of salt and a small piece of salt will have the exact same density.

http://www.youtube.com/watch?v=VDSYXmvjg6M Fast forward through bouyancy – first part of video video…start at 2:33

Density and the Particle Theory of Matter (PTM) The PTM states that different substances have different sized particles.

The PTM also states that there are spaces between the particles.

Ex. Water vapour has a lower density than liquid water. The greater the spaces between the particles, the less particles therefore the lower the density. Ex. Water vapour has a lower density than liquid water. In general, gases are less dense than liquids and liquids are less dense than solids.

CALCULATING DENSITY You must know the mass and volume of a substance first. Mass: the amount of matter in a substance. Volume: the amount of space occupied by the substance.

If you have a regular shaped prism you can use a volume formula to calculate the volume.

To measure the volume of an irregular shape, you will need to determine the amount of water it displaces.

Displacement Displacement - A technique for measuring the volume of an irregularly shaped object by measuring how much water it displaces.

Interactive Displacement http://www.learnalberta.ca/content/mesg/html/m ath6web/index.html?page=lessons&lesson=m6lesso nshell15.swf (fast forward to displacement)

Density = Mass (m)/Volume (V) Calculating Density Formula: Density = Mass (m)/Volume (V)

Science and the NHL

SAMPLE PROBLEMS 1. Find the density of a 10g mass of a substance that has a volume of 2.0 cm³.

What is the volume of the container if the salt completely fills it? 2. You want to put 10g of salt into a container. What is the volume of the container if the salt completely fills it? To get density use the table on page 312.  

3. What is the mass of 1500mL of helium?  

Assignment: Complete practice problems on page 312-314 on loose leaf and pass it in next day as a portfolio mark in this chapter. *Be sure to label your answers with their page number and the number of the question being answered.

Changes in Density True or False? The density of a substance in it’s solid state is greater than the density of it’s liquid state. True! This is because the particles are more spread out and take up more space in a liquid therefore it is less dense.

Density of Water Water, however, is less dense in its solid state (ice) than liquid water. This is why ice cubes float in water! The particles as the water freezes move slightly farther apart then they would be away from each other in liquid form.

As temperature Increases: Particles gain energy and spread out, increasing their volume (space they take up) but decreasing their density. Increasing Temperature= Decrease in density

Temperature and density in Daily Life TIRES: You have to add air to your tires on your car in the winter as the particles of air lose energy as the temperature drops. The particles move close together and take up less space. The tire deflates a little. The density of the air decreases. The same mass of air is distributed in a larger area.

The opposite is true in the summer as air particles spread out due to increase in temperature and energy. They require more space to move around. The air in the tire expands and the tire inflates. The density of the air increases as the mass of air is distributes in a smaller area.

Hot air balloons: Operates by a gas burner heating the air inside it. The air gains energy from the heat and begin to move around more and spread further apart from one another. Some particles leave the balloon. DENSITY has decreased inside the balloon and is less dense than the surrounding air so the balloon floats!