1. Weather Density of Liquids and Solids How much of the country depends on snowfall for the year’s water supply? The mountains get many feet of snow every winter, and then, as temperatures rise in the spring, it melts.

2. Weather, L 3, Density of Liquids and Solids Can scientists measure the snowpack and then predict the amount of water that will be available for consumption the rest of the year? How much water is present in equal volumes of snow and rain?

3. Weather, L 3, Density of Liquids and Solids To answer this question we will look at: - density and phase - converting snowfall to rainfall - the density of ice

4. Weather, L 3, Density of Liquids and Solids Scientists measure the snowpack, or total amount of snow to predict the amount of water that will be available later in the year. These scientists are more interested in how much liquid water the snow represents.

5. Weather, L 3, Density of Liquids and Solids When snow melts, its volume decreases, but the mass remains the same. Volume=the amt of space an object takes up. Density = mass ÷ volume, or D= M / V The density of snow is __<__ than water

6. Weather, L 3, Density of Liquids and Solids Snow Water Mass is not lost, but volume changes.

7. Weather, L 3, Density of Liquids and Solids Unlike water, snow has a wide range of densities. Snow can be fluffy or it can be packed. As long as the density of the substance doesn’t change, its mass and volume are proportional.

8. Weather, L 3, Density of Liquids and Solids The proportionality constant here is the density, D. mass = D x V When we graph the mass versus volume for water, snow, and rain, the data points lie on a straight line that passes through the origin. (0,0)

9. Weather, L 3, Density of Liquids and Solids Volume (mL) What do the slopes of these three lines show us?

10. Weather, L 3, Density of Liquids and Solids Matter changes density when it changes phase. One way to determine the volume of water in the snowpack is to melt it. This isn’t practical, so scientists take samples of new snowfall then determine the density (divide mass by volume.

11. Weather, L 3, Density of Liquids and Solids

12. After pushing the empty aluminum tube into the snowpack, the tube is weighed. The density of the snow is the mass divided by the volume. Lets look at an example.

13. Weather, L 3, Density of Liquids and Solids m snow = D snow x V snow Suppose you have 20 mL of snow with a density of 0.25 g/mL What volume of liquid water will you get when you melt this amount of snow? When snow melts the mass will not change, so

14. Weather, L 3, Density of Liquids and Solids M snow = D snow x V snow and so m snow = (0.25 g/mL) x (20 mL) = 5 g You can also solve this problem using a graph. The graph shows mass versus volume for liquid water.

15. Weather, L 3, Density of Liquids and Solids Converting Snow to Liquid Water Volume (mL) Water

16. Weather, L 3, Density of Liquids and Solids Begin with 20 mL of snow, which is equal to 5 g of water. When snow melts, the mass remains the same, and 5 g of water is equal to 5 mL of snow. The Density of Ice The density of ice is 0.92 g/mL. It is less dense than water (1.0 g/mL).

17. Weather, L 3, Density of Liquids and Solids When water freezes it becomes less dense, and its volume decreases. This unique property of water is due to a special kind of intermolecular force called hydrogen bonding. When water freezes, the molecular motion slows down, and molecules lock into a hexagonal structure due to hydrogen bonding.

18. Weather, L 3, Density of Liquids and Solids

19. Work this out!! Mass=DxV Density=M/VVolume=M/D 2 samples of water. Each in a different phase. Liquid = 20 mL (density is 1.0 g/mL) mass=_______ Ice = 40 mL (density is.92 g/mL) mass=________ One is less dense than the other and will float on the other. Which one? One has more volume than the other. Which one and why?