advertisement

4.10 Density { The amount of mass per unit of volume of a substance Lesson Review How do we find Density? Density = Mass / Volume Example: 16 oz of water with a volume of 8 mL = 16/8 = 2 oz/mL Density is an intensive property, meaning it will not change if you change the mass of the object. Example: 16 oz of water with a volume of 8 mL = 16/8 = 2 oz/mL 32 oz of water with a volume of 16 mL = 32/16 = 2 oz/mL So the density of 16 oz of water is the same as 32 oz of water because the substance is the exact same. That means an Ice cube has the same density as an Iceberg! The Density of a substance will remain the same as long as the substance remains exactly the same, including the phase/state of the substance. Example 2: Substance 1 Substance 2 If you look at substance 1, you can agree it has more red dots than substance 2. If those red dots are atoms, you can agree substance 1 has more atoms than substance 2. Therefore, we can say that substance 1 is more dense than substance 2, because it has more atoms per square unit. In this example, Substance 1 is 16 oz of water and Substance 2 is 16 oz of Ice. Water is more dense than Ice because it has more atoms per square. When water freezes it expands, therefore changing the volume without changing the mass. Substance 1: Mass = 16 oz, Volume = 8 mL Density = 16/8 = 2 oz/mL Substance 2: Mass = 16 oz, Volume = 16mL Density = 16/16 = 1oz/mL More examples: Substance 1 Density Substance 2 Water Water is more dense Ice Ice cube Same density Iceberg Diet coke Diet coke is less dense than coke Regular coke 1 cup of pudding Same density Swimming pool of pudding Conclusion: Density is an intensive physical property and does not change if you increase or decrease the amount of the substance you have. Density of a substance will change if you change or alter the substance in any way (Ex changing phase/state or the substance all together) Practice: Find the density of the following: 1. This substance has a mass of 20 g and a volume of 5 mL. 2. Mercury metal is poured into a graduated cylinder that holds exactly 22.5 mL. The mercury used to fill the cylinder weighs 306.0 g. 1. A block of aluminum occupies a volume of 15.0 mL and weighs 40.5 g. Now put the above 3 substances in order from least dense to most dense based on your answers. Answers: Find the density of the following: 1. Density = 4 g/mL 2. Density = 13.6 3. Density = 2.7 g/mL Now put the above 3 substances in order from least dense to most dense based on your answers. 1. Density = 2.7 g/mL 2. Density = 4 g/mL 3. Density = 13.6