 # DENSITY.

## Presentation on theme: "DENSITY."— Presentation transcript:

DENSITY

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

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

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.

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

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

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

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.

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.

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

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

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.

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

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

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