1. WU 9/7 1.How many sig. figs are in these measurements? a)3.0650 g b. 75800. L c. 53.000 mg d. 0.00065e. 0.0750 s 2.Perform the following calculations: a.2.32 + 4.793b. 6.21 – 3.47 c. 5.343 x 8.2345d. 7.21/4.564

2. Today’s Learning Goals Explain density in terms of particle arrangement. Correctly perform density calculations.

3. Answer these two questions What is mass? –The amount of matter an object has What is volume? –The amount of space an object occupies. Are the following measurements dealing with mass or volume? 10 g 15 mL 2 L 32 kg 2.3 cm 3

4. 3-4 Density Density: the ratio of the mass of an object to its volume. A measure of how closely packed together the particles are.

5. A Dense Concept: More dense = more stuff in less space Less dense= less stuff in more space

6. 3-4 Density Density depends only on the composition of the substance – not quantity or size of sample. 10 g of gold has the same density as 3500 kg of gold –Particles are spaced the same

7. To Float Or Not To Float? Density of water = 1.00 g/mL Density of cork = 0.34 g/cm 3 Density of steel = 7.98 g/cm 3 Predict which substance will float and which will sink

8. How dense are students? You are all magically: 120 lbs/student convert lbs to kg: 2.2 lb-1 kg Find the mass of 30 students. Volume of students = 42 m 3

9. Move Desks next to each other Has the mass changed? Has the volume changed? Calculate the new volume of students Calculate the density

10. 3-4 Density calculations D = m/v Units: g/cm 3 or g/mL or kg/m 3 or kg/L mL and cm 3 have equal magnitude Calculate the density of a substance that has a mass of 10 g and occupies a volume of 15 cm 3.

11. Practice with density EX: Substance A has a mass of 10 g, and a volume of 30 mL. Substance B has a mass of 10 g and a volume of 60 mL. Which has the greater density? (Answer this without calculating)

12. Practice: Calculate the density of a substance with a mass of 5.0 kg and a volume of 3 m 3. Water has a density of 1.00g/mL. Ice floats on water. Is the density of ice greater or less than liquid water? Explain.

13. More Practice: A substance has a density of 1.5 g/mL and a volume of 40 mL. What is the mass of this substance?