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Density

Density. 1 kg of feathers. 1 kg of rock. Which do you think would have the greater mass? Greater volume? Why ?. Same mass! Larger volume. Same mass! Smaller volume. Volume vs. Mass. Volume is the amount of space something takes up. Mass

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Density

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  1. Density

  2. 1 kg of feathers 1 kg of rock Which do you think would have the greater mass? Greater volume? Why? • Same mass! • Larger volume • Same mass! • Smaller volume

  3. Volume vs. Mass Volume is the amount of space something takes up Mass is the amount of matter in an object (how “heavy” something is)

  4. Finding Mass Place the object on a scale or balance Units should be grams (g) or kilograms (kg)

  5. Finding Volume of a Regular Shape An object with a “regular” shape is measurable and symmetric • Measure length (L), width (W) and height (H) • Multiply L x W x H • Make sure units make sense (cm3, m3) 4 cm x 6 cm x 5 cm = 120 cm3 Conversion Factor: 1 cm3 = 1mL

  6. Finding Volume of an Irregular Shape An object that can not easily be measured • Use displacement • Fill a graduated cylinder or overflow can with water • Measure how much water goes up/spills out when object is placed in water Remember: 1 cm3 = 1mL

  7. DENSITY • Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object. • Density is the amount of matter within a certain volume (how much “stuff” is crammed into something) Units of Density: g/cm3 or g/mL Depends on the units used for mass and volume

  8. Density of Phases of Matter Which phase of matter is the densest? Which phase of matter is the least dense? *Usually the solid phase of a substance will sink in it’s liquid phase because it is more dense SOLID GAS • Water is an exception! • Because water expands when it freezes, solid water (ice) is actually less dense than liquid water

  9. Densities of Common Substances (g/mL) Metals Aluminum 2.7 Copper 8.9 Gold 19.3 Iron 7.8 Lead 11.3 Silver 10.5 Liquids Pure Water 1.0 Sea Water 1.03 Alcohol 0.8 Gylcerine 1.3 Milk 1.03 Turpentine 0.9 Mercury 13.6 Gasoline 0.7 Note: The density of a substance will always be the same, regardless of it’s shape or size i.e. the density of pure water is always 1 g/mL Solids Bone 2 Brick 1.8 Cork 0.2 Ice 0.92 Marble 2.7 Paraffin 0.9 Rubber 1.2 Bamboo 0.3 Oak Wood 0.7 Pine Wood 0.6

  10. Finding Density • Density (D) is mass (m) per unit volume (v) • per = divided by • D = m/v (m ÷ v) Formula: D = M / V M = D x V V = M / D M = mass V= volume D = density Divided by Multiplied by

  11. Practice Problem #1 If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density. Given: Mass = 35 grams Volume = 7 cm3 Density = ? (g/ cm3) Formula: D = M / V Solution: D = 35 g / 7 cm3 D = 5 g/cm3

  12. Practice Problem #2 A rectangular block of copper metal has a mass of 1896 g. The dimensions of the block are 8.4 cm by 5.5 cm by 4.6 cm. From this data, what is the density of copper? Given: M = 1896 grams V = 8.4 cm x 5.5 cm x 4.6 cm = 212.52 cm3 D = ? (g/ cm3) Formula: D = M / V Solution: D = 1896 g / 212.52 cm3 D = 8.92 g/cm3

  13. Practice Problem #3 Find the mass of 250.0 mL of benzene. The density of benzene is 0.8765 g/mL. Given: V = 250.0 mL D = 0.8765 g/mL M = ? g Formula: M = D x V Solution: M = 0.8765 g/ mL x 250.0 mL M = 219.13 g

  14. Practice Problem #4 What volume of silver metal will has a mass of exactly 2500.0 g. The density of silver is 10.5 g/cm3. Given: M = 2500.0 g D = 10.5 g/cm3 V = ? cm3 Formula: V = M / D Solution: V = 2500.0 g / 10.5 g/cm3 V = 238.10 cm3

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