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DENSITY

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DENSITY

Pb Pb

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

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PbPb

WHICH BLOCK HAS THE GREATER DENSITY?

IF YOU ANSWERED, “THEY HAVE THE SAME DENSITY.” YOU ARE CORRECT!!!

WHY?

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

WHY?

2. Density is a ratio of Mass to Volume (D=M/V).

Let’s do some calculations to explore this.

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Let’s take measurements of each block.

Small block:mass: 272.16 g

linear measurements:

2.00cm x 3.00cm x 4.00cm

Large Block:mass: 1360.8 g

linear measurements:

4.00cm x 5.00cm x 6.00cm

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Let’s calculate the volume of each block.

Small block:mass: 272.16 g

Volume Calculations:

2.00cm x 3.00cm x 4.00cm = 24.0 cm3

Large Block:mass: 1360.8 g

Volume Calculationss:

4.00cm x 5.00cm x 6.00cm = 120cm3

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Now let’s calculate the density of each.

Small block:mass: 272.16 gVolume: 24.0 cm3

DENSITY=M/V

272.16 g = 11.3 g 24.0cm3 cm3

Large Block:mass: 1360.8 g Volume: 120cm3

DENSITY=M/V

1360.8g = 11.3g 120cm3 cm3

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Small block:mass: 272.16 gVolume: 24 cm3

272.16g = 11.3 g =DENSITY

24.0cm3 cm3

Large Block:mass: 1360.8 g Volume: 120cm3

1360.8g = 11.3g = DENSITY

120cm3 cm3

Note: the mass to volume ratios (DENSITIES) are the same.

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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.

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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 = g1000 mL 1L

11.3 g mL

11300

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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 = cm340.17454 g1.00 lb

cm3

11.3 g40.2 cm3

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1.00 lb 454 g cm3 = 40.17 cm3

1.00 lb 11.3 g

Let’s compare the two solutions.

1.00 L 1000 mL 11.3 g = 11300 g 1 L mL

Compare how density was used in the two solutions.

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Now work with someone next to you to solve this problem.

Problem: A rock having a mass of 136.17 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 = 48.5 - 23.0 =25.5 mLDensity = 136.17 g = 5.34 g = 5.34 g 25.5 mL mL cm3

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Cooking oil has a density of approximately 0.952 g/mL.

a. Determine the mass of 550 mL of cooking oil.

= g550 mL 0.952 g

mL523.6

520 g

b. Determine the volume of 870 g of cooking oil.

= mL870 g mL

0.952 g913.9

910 mL

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Densities of Some Common Materials

Substance Density g/cm3 water (25oC) 1.00 ice (0oC) 0.917Gold 19.31Lead 11.3sand ??

Does density change with temperature?