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

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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.

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**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

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**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

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**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

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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.

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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 = g 1000 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 = cm3 454 g 1.00 lb cm3 11.3 g 40.17 40.2 cm3

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**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.

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**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

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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. 550 mL = g 523.6 520 g b. Determine the volume of 870 g of cooking oil. 870 g = mL 913.9 910 mL

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**Densities of Some Common Materials Substance Density g/cm3 **

water (25oC) ice (0oC) Gold Lead sand ?? Does density change with temperature?

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