Density. How tightly the atoms are packed together in an object

Transcription

1 Density How tightly the atoms are packed together in an object

2 Mass vs Weight Mass is the amount of matter in an object. (it doesn t change) Weight is determined based on the amount of gravity pulling an object down. (It can change. The greater the gravitational pull the greater the weight)

3 Volume Measurement of the amount of space an object takes up Measured in milliliters (ml) or cm 3

4 Which do you think would have the greater volume? The greater mass? Why? 1 kg of feathers 1 kg of rocks

5 Which one is more dense? Demonstration: People in a square How about this: Which square is more dense?

6 Which one is more dense? Now which one is more dense?

7 Ways to Affect Density Change Mass AND Keep Volume Same Increase the mass increase density Decrease the mass decrease in density Which container has more density? A B

8 Ways to Affect Density Change Volume AND Keep Mass Same Increase the volume decrease density Decrease the volume increase density Which container has more density? A B

9 In your notebook illustrate the answer to the following question: What 2 ways will INCREASE density?

10 What 2 ways will INCREASE density? Keep the same mass AND decrease the volume Keep the same volume AND increase the mass

11 What 2 ways will INCREASE density? Keep the same mass AND decrease the volume Keep the same volume AND increase the mass

12 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/cm 3 (solid)

13 DENSITY - an important and useful (qualitative) intensive physical property Density mass (g) volume (cm3) Mercury Platinum Aluminum 13.6 g/cm g/cm g/cm 3

14 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.

15 Density Calculations Regularly Shaped Solid : mass = balance volume = measure (l x w x h) Irregularly Shaped Solid: mass = balance volume = water displacement

16 Density Calculations Liquid: volume = read graduated cylinder mass = tare graduated cylinder, mass liquid

17 Problem A piece of copper has a mass of g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm 3 ). Density mass (g) volume (cm3) M D V

18 Strategy 1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculat e the density.

19 SOLUTION 1. Get dimensions in common units mm 1cm 10 mm 2. Calculate volume in cubic centimeters. 3. Calculate the density g = 9.0 g / cm cm = cm (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm 3 Note only 2 significant figures in the answer!

20 Problem: Mercury has a density of 13.6g/cm 3. What is the mass if 95 ml of mercury in grams.

21 Strategy First, note that 1 cm 3 = 1 ml 1. Use density to calculate mass (g) from volume.

22 Strategy 1. Convert volume to mass 95 cm g cm 3 = 1.3 x 10 3 g

23 Learning Check Osmium is a very dense metal. What is its density in g/cm 3 if g of the metal occupies a volume of 2.22 cm 3? 1) 2.25 g/cm 3 2) 22.5 g/cm 3 3) 111 g/cm 3

24 Solution 2) Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = g = volume 2.22 cm 3 = g/cm 3 = 22.5 g/cm 3

25 Learning Check Osmium is a very dense metal. What is its density in g/cm 3 if g of the metal occupies a volume of 2.22 cm 3? 1) 2.25 g/cm 3 2) 22.5 g/cm 3 3) 111 g/cm 3

26 Volume Displacement A solid displaces a matching volume of water when the solid is placed in water. 25 ml 33 ml

27 If you have 2 or more substances, the MORE dense substance will be on bottom The LESS dense substance will be on top

28 The density of five liquids are measured as follows: Liquid 1: 1.0 g/ml Liquid 2: 1.38 g/ml Liquid 3: 0.77 g/ml Liquid 4: 2.95 g/ml Liquid 5: g/ml Liquid 5 Liquid 3 Liquid 1 Liquid 2 Liquid 4 Draw a picture of all 5 liquids in a test tube how they would layer according to density

29 Liquid Layers Check out this picture. Which layer has the highest density? Which layer has the lowest density? Imagine that the liquids have the following densities: 10g/cm 3. 3g/cm 3. 6g/cm 3. 5g/cm 3. Which number would go with which layer? 5 g/cm 3 3 g/cm 3 6 g/cm 3 10 g/cm 3

30 Liquid Layers Try with your neighbor Which liquid has the highest density? Which liquid has the lowest density? Which liquid has the middle density?

31 Liquid Layers Try on your own! Imagine that the liquids on the right have the following densities: 15g/cm 3 10g/cm 3 3g/cm 3 9g/cm 3 7g/cm 3 12g/cm 3 Match the colors to the correct densities. 3g/cm 3 9g/cm 3 12g/cm 3 7g/cm 3 10g/cm 3 15g/cm 3

32 Learning Check What is the density (g/cm 3 ) 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/ cm 3 2) 6 g/m 3 3) 252 g/cm 3 25 ml 33 ml

33 Density Let s see if you can: 1. Define density 2. Calculate the density of a given object if given the volume and mass 3. Calculate the volume or mass if the density is given with the volume or mass

34 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) V 2) W 3) W K K V K V W

35 Learning Check The density of octane, a component of gasoline, is g/ml. What is the mass, in kg, of 875 ml of octane? 1) kg 2) 614 kg 3) 1.25 kg

36 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) L 2) 1.25 L 3) 1.83 L 4) 548 L

37 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/cm 3 ) are obtained from the cans? (1 kilogram = 2.2 pounds) 1) 1.00 L 2) 2.00 L 3) 4.00 L

38 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.

39 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.