Télécharger la présentation
## Density

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Density**How tightly the atoms are packed together in an object**DensityAt the conclusion of our time together, you should be**able to: Define density Calculate the density of a given object if given the volume and mass Calculate the volume or mass if the density is given with the volume or mass**Density**• Density = mass volume • Mass = the amount of matter in an object • Volume = the amount of space the object takes up • Units = g/mL (liquid) OR g/cm3 (solid)**Platinum**Mercury Aluminum DENSITY - an important and useful (qualitative) intensive physical property 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3**Familiar Saying**A rotating lithoidal fragment never accrues lichen. A rolling stone gathers no moss!!**Density Calculations**M D V Cover up whatever unit you are solving for, the two units remaining will show you how to solve the problem.**Density Calculations**• Regularly Shaped Solid : mass = balance volume = measure (l x w x h) • Irregularly Shaped Solid: mass = balance volume = water displacement**Density Calculations**• Liquid: volume = read graduated cylinder mass = tare graduated cylinder, mass liquid**ProblemA piece of copper has a mass of 57.54 g. It is 9.36**cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3). M D V**Strategy**1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density.**SOLUTION**1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density. (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3 Note only 2 significant figures in the answer!**Euphemisms in Science We all know that some politicians and**government spokesmen use certain euphemistic phrases to give an aura of respectability to descriptions of events or actions which would be offensive when expressed in plain English. The following is a list of Euphemisms in Science and their translations into plain English. “These results are correct within an order of magnitude...” Wrong!**PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is**the mass of 95 mL of Hg in grams? In pounds?**Strategy**First, note that1 cm3 = 1 mL 1. Use density to calculate mass (g) from volume. 2. Convert mass (g) to mass (lb) Need to know conversion factor = 454 g / 1 lb**Strategy**1. Convert volume to mass 2. Convert mass (g) to mass (lb)**Learning Check**Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupies a volume of 2.22 cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3**Solution**2) Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = 50.00 g = volume 2.22 cm3 = 22.522522 g/cm3 = 22.5 g/cm3**Learning Check**Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupies a volume of 2.22 cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3**Volume Displacement**A solid displaces a matching volume of water when the solid is placed in water. 33 mL 25 mL**Learning Check**What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? 1) 0.2 g/ cm3 2) 6 g/m3 3) 252 g/cm3 33 mL 25 mL**A.P. TEST IN AMERICAN HISTORY**• There is a red telephone on your desk. Start World War III. Report in length on its socio-political effects on the United States, if any.**DensityLet’s see if you can:**Define density Calculate the density of a given object if given the volume and mass Calculate the volume or mass if the density is given with the volume or mass**Learning Check**Which diagram represents the liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) 2) 3) K W V V K W W V K**Learning Check**The density of octane, a component of gasoline, is 0.702 g/mL. What is the mass, in kg, of 875 mL of octane? 1) 0.614 kg 2) 614 kg 3) 1.25 kg**Learning Check**If blood has a density of 1.05 g/mL, how many liters of blood are donated if 575 g of blood are given? 1) 0.548 L 2) 1.25 L 3) 1.83 L 4) 548 L**Learning Check**A group of students collected 125 empty aluminum cans to take to the recycling center. If 21 cans make 1.0 pound of aluminum, how many liters of aluminum (D = 2.70 g/cm3) are obtained from the cans? 1) 1.00 L 2) 2.00 L 3) 4.00 L**Water has a density of 1.0 g/ml and mercury (Hg) has a**density of 13.6 g/ml. Which is heavier, a quart of water or a quart of mercury? If we have equal volumes of two different substances, then the one with the greater density will have the greater mass.**15 Helpful Hints On The Lab Report from Mr. T’s Vast Lab**Experience!!! Hint #11. Given the most inappropriate time for something to go wrong, that's when it will occur.**Which is heavier, a ton of feathers or a ton of bricks?**Neither • Which is larger? Feathers • If two objects have the same mass, the one with the higher density will be smaller.