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Density

Density. The concentrationof matter in an object is known as density . Computing Density. RT = Pg. 1. Density = mass ( g ) volume (cm 3 ). DETERMINE MASS : Use a triple beam balance to determine the mass of the object. DETERMINE VOLUME :

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Density

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  1. Density The concentrationof matter in an object is known as density.

  2. Computing Density RT = Pg. 1 Density = mass (g) volume (cm3) DETERMINE MASS: Use a triple beam balance to determine the mass of the object. DETERMINE VOLUME: One way to determine volume is to use a graduated cylinder to determine the displacement of water achieved by placing the object in a predetermined volume of water.

  3. Computing Density DETERMINE VOLUME: Another way to determine volume is to measure the height, length and width of a solid that is cubic or rectangular in design. The formula shown will determine the volume of the object.

  4. Sample Density problem #1 A student determines the mass of a rock sample to be 156.3 g. The volume of the same rock sample is 51.3 cm3. What is the density of the rock sample? Density = mass (g) volume (cm3) Density = 156.3 g 51.3cm3 Density = 3.0 g/cm3

  5. Sample Density problem #2 Given the information provided, determine the density of the toy? Mass of Toy Dinosaur = 10 g Density = mass (g) volume (cm3) Volume of Toy Dinosaur = ? Density = 10 g = 12.5 g/cm3 0.8cm3

  6. Determining Relative Density The densities of objects in gases and fluids can be determined by observing the “flotation” of the object in the fluid or gas Density of helium gas = 0.2 g/cm3 Density of air= 1.2 g/cm3 Objects with lower densities than the fluid or gas they are in will float above objects with higher densities.

  7. Determining Relative Density Liquid water has a density of 1.0 g/mL. Determine the relative densities of the objects in the glasses of water. The object has a relative density less than water because it floats. The object has a relative density more than water because it sinks.

  8. Physical Changes That Affect Density Changes in temperature and pressure can change the densities of substances …. especially gases. If temperature of a gas increases while pressure is constant… -- molecules move faster -- molecules will move farther apart (expansion) -- less mass per unit volume DENSITY WILL DECREASE Example: Air that is heated is less dense than air that is cooled. Therefore, heated air will rise above cooled air.

  9. Physical Changes That Affect Density Changes in temperature and pressure can change the densities of substances …. especially gases. If temperature of a gas decreases while pressure is constant… -- molecules move slower -- molecules will move closer together (compression) -- larger mass per unit volume DENSITY WILL INCREASE Example: Air that is cooled is more dense than air that is heated. Therefore, cooled air will sink below heated air.

  10. Physical Changes That Affect Density Changes in temperatureand pressure can change the densities of substances …. especially gases. If the pressure on a gas increases while the temperature is constant… -- molecules will move closer together (compression) -- larger mass per unit volume DENSITY WILL INCREASE Pressure Pressure

  11. Phases of Matter and Density Matter on Earth exists in three phases: solid, liquid, gas. Most substances will increases in density as the substance changes phase from gas to liquid and from liquid to solid. Water’s highest density exists in its liquid phase (3.98 C). Liquid Iron = 7.2 g/cm3 Solid Iron = 7.8 g/cm3 Ice = 0.97 g/cm3 Liquid Water = 1.0 g/cm3

  12. Density vs. Object Size and Shape Quartz crystal: Mass = 10.9 g The density of an object will NOT change should an object change its size and/or shape. Density of quartz 2.6 g/cm3 Quartz globe: Mass = 88..9 g

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