1. DENSITY

2. DENSITY Pb Pb
Both of the above blocks consist of pure lead (Pb)

3. Pb Pb
WHICH BLOCK HAS THE GREATER DENSITY?
IF YOU ANSWERED, “THEY HAVE THE SAME DENSITY.”
YOU ARE CORRECT!!!
WHY?

4. WHY?
1. Both of the above blocks consist of pure lead (Pb)
2. Density is a ratio of Mass to Volume (D=M/V).
Let’s do some calculations to explore this.

5. Let’s take measurements of each block.
Small block:
mass: g
linear measurements:
2.00cm x 3.00cm x 4.00cm
Large Block:
mass: g
linear measurements:
4.00cm x 5.00cm x 6.00cm

6. Let’s calculate the volume of each block.
Small block:
mass: g
Volume Calculations:
2.00cm x 3.00cm x 4.00cm =
24.0 cm3
Large Block:
mass: g
Volume Calculationss:
4.00cm x 5.00cm x 6.00cm = cm3

7. Now let’s calculate the density of each.
Small block:
mass: g
Volume: 24.0 cm3
DENSITY=M/V
g = 11.3 g
24.0cm cm3
Large Block:
mass: g
Volume: 120cm3
DENSITY=M/V
1360.8g = 11.3g
120cm cm3

8. Small block:
mass: g
Volume: 24 cm3
272.16g = 11.3 g =DENSITY
24.0cm cm3
Large Block:
mass: g
Volume: 120cm3
1360.8g = 11.3g = DENSITY
120cm cm3
Note: the mass to volume ratios (DENSITIES) are the same.

9. Density as a Conversion Factor
Note: The units of density are in a ratio form, so density can be used as a conversion factor to change mass to volume or volume to mass.
Let’s explore this.

10. Problem: Determine the mass of a 1.00 L sample of Pb.
(The density of Pb is 11.3 g/cm3, 1 L = 1000mL =1000 cm3
Solution:
1. What are the units of what we are looking for?
__________________ = g (mass units = grams)
2. What do we have?
1.00 L______________ = g
3. Now convert L into g using density
1.00 L = g
1000 mL 1L
11.3 g mL
11300

11. Problem: Determine the volume of a 1.00 lb (454 g) sample
of Pb. (The density of Pb is 11.3 g/cm3)
Solution:
1. What are the units of what we are looking for?
__________________ = cm3 (volume units)
2. What do we have?
1.00 lb______________ = cm3
3. Now convert lb into cm3 using density
1.00 lb = cm3
454 g
1.00 lb
cm3
11.3 g
40.17
40.2 cm3

12. Let’s compare the two solutions.
1.00 L mL g = g
1 L mL
1.00 lb g cm = cm3
1.00 lb g
Compare how density was used in the two solutions.

13. Now work with someone next to you to solve this problem.
Problem: A rock having a mass of g was placed in a graduated cylinder containing water with an initial reading of 23.0 mL. The water level rose to a reading of 48.5 mL. Calculate the density of the rock.
Volume = =25.5 mL
Density = g = 5.34 g = 5.34 g
25.5 mL mL cm3

14. Cooking oil has a density of approximately 0.952 g/mL.
a. Determine the mass of 550 mL of cooking oil.
550 mL
= g
523.6
520 g
b. Determine the volume of 870 g of cooking oil.
870 g
= mL
913.9
910 mL

15. Densities of Some Common Materials Substance Density g/cm3
water (25oC)
ice (0oC)
Gold
Lead
sand ??
Does density change with temperature?