1. Topic 5: Density Density: The mass per unit volume of a substance

2. Density Density can be described as the “crowdedness” of the particles that make up matter. – Elevator example Particle model states that the size of the particles determines how many particles can fit into a given space. Each substance has it’s own density based on how close together the particles are.

3. Density of Solids, Liquids, Gases Solid particles have very little space between them. Therefore, solids have a higher density than liquids. Liquid particles have slightly larger spaces between them and therefore liquids are less dense than solids. Gas particles have larger spaces than both solids and liquids, therefore gases are less dense than BOTH solids and liquids. There are some exceptions (ice)

4. Density Solids can move freely through liquids and with even less effort through gases. This is because you do not have to move as many particles apart in gases as you do in water. Why can we not push apart the particles in a solid?

5. How does temperature affect density? As temperature increases, a substance will change from solid, to liquid, to gas. Particles spread out and move faster as they gain energy, making them take up more space. When particles take up more space, the density of the substance will decrease – less particles can fit in a given “space”

6. Can the density of the liquid state of one substance be greater than the density of the solid state of another substance? Table 1.5 p.52

7. How are Mass and Volume Related? Mass: the amount of matter in a substance – Usually measured in grams (g) or kilograms (kg) Volume: a measurement of the amount of space occupied by the substance. – Usually measured in milliliters (mL) or liters (L) Weight: the force of gravity exerted on a an object. – On earth gravity pulls on an object towards the Earth at 9.8N for every Kg of it’s mass – All forces are measured in Newtons (N)

8. Formula for Density Density is a mass to volume ratio Mass : Volume Density of a substance is determined by calculating its mass to volume ratio. Do this by dividing the objects mass by its volume. Density = Mass (g) D = M Volume (cm 3 or mL) V 1 cm 3 = 1 mL

9. Examples 1.An object has a mass of 10g and a volume of 2cm 3. Find its density. 2.A glass of juice has a volume of 50mL and a mass of 65g. What is the density? 3.The density of a substance is 16g/mL. The volume is 36mL. What is the mass of the substance?