1. Today is Thursday (!), February 12 th, 2015 Pre-Class: Choose one: Why does wood float? or Which is heavier, a kilogram of lead or a kilogram of hydrogen gas? http://fineartamerica.com/images-medium/the-schooner-margaret-todd-bar-harbor-maine-bob-orsillo.jpg Stuff You Need: Calculator In This Lesson: Density (Lesson 5 of 6)

2. Today’s Agenda Density! Where is this in my book? – P. 89 and following…

3. By the end of this lesson… You should be able to calculate density of a given substance.

4. Density The density of an object (that’s one of its intensive properties, a physical property) is the relationship between its mass and volume. Density = mass / volume – Mass = volume * density – Volume = mass / density M D V

5. Density To put it another way, if two objects take up the same amount of space but have different masses, one must be more dense than the other. Alternatively, if two objects have the same mass but different densities, their volumes must be different. – I think you get the idea…

6. Density Facts Density is always expressed in terms of [mass]/[volume]. – For us, it will typically be g/cm 3 or g/mL. – Don’t forget the units! Water has a density of 1 g/cm 3. – Funny how water always has nice round numbers, huh? 1 cm 3 of water has a mass of 1 g.

7. Buoyancy To see if something is buoyant (can float), you need two densities: – The object’s. – The fluid’s. Object density > fluid density? Object sinks. Object density < fluid density? Object floats. Object density = fluid density? Object “kinda” floats. – For water, since its density is 1 g/mL, anything higher than 1 will sink; lower will float. Dense water? Try the Dead Sea (video).

8. Buoyancy http://i.telegraph.co.uk/multimedia/archive/02109/CostaConcordia-WEB_2109037b.jpg http://cdn.theatlantic.com/static/infocus/costa011612/c01_36991800.jpg Less Dense Than Water More Dense Than Water The Costa Concordia, which wrecked off Italy’s coast in January 2012.

9. Density and Problem-Solving Here’s a challenge question for you: – Imagine you’re a king (or queen), and you have a royal crown-maker. – Problem is, the dude looks really suspicious. Has funny eyebrows or something. – So you suspect that maybe he’s not making your crowns out of solid gold like you said. Instead, he might be cutting the gold with something gold-like, but cheaper. – How do you prove him innocent or guilty without destroying one of your crowns? – Discuss!

10. Density and Problem-Solving Turns out this was a real problem faced by this guy: His name was Archimedes and he solved this problem. What’d you come up with? http://charlespaolino.files.wordpress.com/2010/07/archimedes_16201.jpg

11. How Archimedes Solved The Problem Archimedes noticed the property of displacement (how much matter is moved) when he got into his bathtub. He realized this is a way to measure volume. He was so excited by his discovery (early science dork) that he supposedly jumped out of his bathtub and ran naked down the streets of Sicily shouting “Eureka!” (“I have it!”)

12. Let’s try some examples ourselves: Grab your calculators, grab the whiteboards, [don’t] grab your partners, and let’s try some density problems right now. http://www.algebralab.org/practice/practice.aspx?file=word_density.xml

13. Density Problem #1 What is the density of a piece of wood that has a mass of 25.0 grams and a volume of 29.4 cm 3 ? 0.850 g/cm 3

14. Density Problem #2 A piece of wood that measures 3.0 cm by 6.0 cm by 4.0 cm has a mass of 80.0 grams. What is the density of the wood? 1.1 g/cm 3 Would it float in water? – No! It’s more dense than water, so it would sink.

15. Density Problem #3 A group of gold-colored beads was measured to have a mass of 425 grams. By water displacement, the volume of the beads was calculated to be 48.0 cm 3. Given the following densities, identify the metal: (1 mL = 1 cm 3 ) A.Gold: 19.3 g/mL B.Copper: 8.86 g/mL C.Bronze: 9.87 g/mL

16. Density Problem #3 A group of gold-colored beads was measured to have a mass of 425 grams. By water displacement, the volume of the beads was calculated to be 48.0 cm 3. Given the following densities, identify the metal: (1 mL = 1 cm 3 ) A.Gold: 19.3 g/mL B.Copper: 8.86 g/mL C.Bronze: 9.87 g/mL

17. Density Problem #4 If I throw a plastic ball into a pool for my dog to retrieve, what volume must the ball be to float? The mass is 125 grams and the density should be 0.500 g/mL. 250 mL [density = mass/volume]

18. Density Problem #5 CHALLENGING: If the ball happens to spring a leak, how many mL of water can the ball take in before it sinks? [remember, ball is 125 g and we designed it to be 250 mL] – Greater than 125 mL

19. Density Problem #6 CHALLENGING: What is the mass of a cylinder of lead that is 2.50 cm in diameter and 5.50 cm tall? The density of lead is 11.4 g/mL and the volume of a cylinder is V=πr 2 h. – Volume of the cylinder is 8.59π mL (≈27 mL) – Mass of cylinder = 308 g [Density * Volume = Mass]

20. Density Problem #7 The volume of a solution is shown by the graduated cylinder below. If the mass is 60.75 grams, what is the density? 1.350 g/mL http://www.algebralab.orit to be 250 mL].g/practice/practice.aspx?file=word_density.xml

21. Density Problem #8 An ice cube measuring 5.80 cm by 5.80 cm by 5.80 cm has a density of 0.917 g/mL. What is the mass? 179 grams

22. Density Problem #9 Gasoline is a non-polar liquid that will float on water. 450 grams of gasoline is spilled into a puddle of water. If the density of gasoline is 0.665 g/mL, what volume of gasoline is spilled? 677 mL

23. Density Problem #10 The density of aluminum is 2.70 g/mL. If the mass of a piece of aluminum is 244 grams, what is the volume of the aluminum? 90.4 mL

24. DENSITY CHALLENGER Also known as “The Density Boss.” A little aluminum boat (mass of 14.50 g) has a volume of 450.00 cm 3. The boat is placed in a small pool of water and carefully filled with pennies. If each penny has a mass of 2.50 g, how many pennies can be added to the boat without it sinking? 174 pennies

25. Now it’s your turn to work alone… Try the Density Practice Problems worksheet.

26. So now then… Let’s put this to the test in a virtual lab called Density Laboratory. It’s found on ExploreLearning.com. Log-in information will be on the next slide or (recommended) posted on my teacher site on the Chemistry Links. Complete the accompanying worksheet. [Log-in Instructions]

27. Density to Water You may have noticed that there is a relationship between floating/sinking and the density of the water. The specific gravity of a substance is the ratio of that substance’s density to the density of water. – Specific gravity greater than 1? It’s more dense than water. Liquids are usually measured with a hydrometer.

28. Density Lab We’re going to finish our lessons on density with a look into a less electronic exercise. The Density Lab!

29. Closure and Homework Tonight for homework, make sure your Coca- Cola lab is done. Make sure your density virtual lab is done. Make sure your density worksheets are done. Then read pages 89-92. Do questions #85-87 on page 97.