Density Labs. Now lets get in to some labs that really let you dig in to the concept of density. We will do a series of three groups of labs.

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1 Apologia Chemistry Page 1 Density Labs Monday, September 15, :31 PM Slides Notes Now lets get in to some labs that really let you dig in to the concept of density. We will do a series of three groups of labs. The first set will explore how you can control if something sinks or floats. 09 pick up here The first thing that you must realize is that density is relative. The object's density compared to the liquid's density is what matters here. Water has been set as the standard. When you compute water's density it conveniently comes out to be a 1. Let's take three small balls all with the same volume but with different masses. That will make them all have different densities. The first one we will explore is the one with the lowest density. If the grams is smaller than the volume, your object will be less dense than the density of water and it will float in water. If the grams are the same as the volume, your object will be neutrally buoyant in water and it will hover about in the middle of the container of water. If the grams are bigger than the volume, your object will sink because it is more dense than water. Oil, which has a density of 0.197, is much less dense than water. That is why you see it float on the water Italian Salad dressing. All the balls would sink in oil

2 Apologia Chemistry Page 2 because all of them would have a density larger than When you think of something heavy, you might think of a bowling ball. Will it float or will it sink? Well, it will depend on the mass to volume ratio, or density, compared to water. Bowling balls can range from 6 lbs. up to 16 lbs. and be the same circumference. If you have a bowling ball at home, make a hypothesis as to whether it will sink or float and test it to see if you are correct. This set of labs was to be focused on controlling sinking or floating, so we better get to the way you can control one variable at a time and get that controlling started. You have two variables for your object: mass and volume. However, you also have control over the liquid too. In this lab, you are going to control sinking and floating by controlling the density of the liquid. You can do this by adding salt to the water to increase its density. Notice that the computed density of a fresh egg is very similar to water's density. If you add salt you can begin to make the density of the water higher than the density of the egg. This will make the egg first begin to stand off the bottom of the beaker and if you add enough salt you can get it to being neutral in density to the salt water which will make it hover in the middle. Add more and the egg will then float. Give this lab a try at home.

3 Apologia Chemistry Page 3 In this lab, you will be controlling the mass of the object which will give you a neat toy called a Cartesian Diver. What you do first is set a beaker and a sports drink or two-liter bottle completely to the top with water and let it sit for several hour so that it reaches room temperature. Next, calibrate your pipette in the beaker of room temperature water by filling it with water until it hovers in the middle of the water in the beaker. Without letting the water drip out, transfer the pipette in to the drink bottle. It should move to the middle of the column of water if you calibrated it well and didn't lose water from the pipette. Add water from the beaker if needed so that the bottle is completely full, even overflowing a little. Screw the cap on tightly. Now, squeeze the bottle. The pipette will act like a diver and go up and down as you squeeze it. Why? Well, I told you that you were going to change one variable: mass. Look closely at the diver when you squeeze the bottle, Can you see the water level rise in the pipette? The volume cannot change, but the added water in the pipette makes the mass greater. This makes it sink. Release the pressure and the extra water goes back out to the starting amount and it moves back up to its hovering position. In this one, the volume changes so that floating and sinking is controlled. It is a lava lamp. When the solid is at the bottom near the heater, it begins to soften and the volume expands. Since its density is very close to the density of the liquid, it doesn't take long before the density is lighter than the liquid and it begins to rise. At the top it cools and the density becomes greater than the liquid and it begins to sink. This process can repeat over and over making a relaxing display of motion.

4 Apologia Chemistry Page 4 While we are on floating and sinking, I want you to think about the phenomenon of ice in water. For most substances, when they become a solid they shrink. Not water though. Water is the most dense at about 4 degrees Celsius. The molecules pack up tightly. When they get that close though, the positively and negatively charged sides of the molecule begins to line up somewhat like you see when you have magnets with north and south pole line up. This makes the molecules create a crystal lattice with space between the molecules. The ice expands which makes the volume larger yet the mass stays the same. That drops the density and the ice floats. Now, lets look at some of the fun we can have with layering liquids because of density. Fill an aquarium tube about half full with water. Add some food coloring to make it easy to see if you like. Now change the height of the ends of the tube. Do not close the ends with your thumbs. What happens to the water as you make one side higher and then the other? Do they stay the same? Now add oil to one open end. Repeat the height changes that you did a few moments ago. Does the water and oil act the same as the water alone as far as the height of the liquid? Why?

5 Apologia Chemistry Page 5 This one is a pretty and fun whay to play around with density and liquids. You will start out by creating some liquids with different densities and adding food coloring of different colors to each one. You can see the liquids we selected and they worked great. Stick a clear straw in to an apple half. Warning, don't use plastilin class as a base if one of your liquids is alcohol. The alcohol will start to melt your Plastilin clay. Now, fill up a clear straw with the liquid adding in the densest to the least dense one by one gently. A small funnel or pipette is a great tool for this. Enjoy your rainbow straw by displaying it. You have probably heard that water and oil don't mix and you see it in Italian salad dressing. You have to shake the bottle to get them to mix and it doesn't take long sitting still and they are separated again. You can make them mix and stay mixed though. Just add an emulsifier. Egg white is a great one. If you look at the ingredients list for real mayonnaise, you will discover is is oil, water, and egg white. Soap works like an emulsifier too and is why you can wash something oily and get it clean again. Try that without soap in just water. It doesn't work so well.

6 Apologia Chemistry Page 6 Next up: What is This? You can learn a lot about a substance by finding ways to make the density more obvious. For instance, we took several cans of different cans of soda and placed them in the water. They each would float at different levels. Here is the data arranged by cans that floated the highest to the ones than sunk the deepest. Can you hypothesize why some would float and some would sink based on density just by what you see in the labelling of the sodas?

7 Apologia Chemistry Page 7 When plastic gets recycled, density can be used to identify the type of plastic it is based on density. We created a column of liquid with three different densities as shown. We then could add in the various types of plastic chips and get a pretty good estimate of what the density was. Then we could compare it to a chart of densities for the common types of plastic. We were able to identify nearly all the chips we had. So far, we have focused a lot of attention on liquids. What about gasses and solids? Can you control sinking and floating with those? Well, gasses sink and float all the time and give us some wild weather. Wen cold fronts of air which are dense collide with warn fronts, the warm front air which carries a lot of water vapor ends up going up and over the denser cold air. The air is colder the higher that air goes and that makes the water vapor start to condense into droplets. We end up with rain, snow, sleet, or ice. Often, all the motion can cause thunderstorms too.

8 Apologia Chemistry Page 8 Okay, well then what about solids. I used density and solids to play a little trick on my boys. I told them I had a jar of magic M&M's that when you shae it a surprise would appear. I had hidden a plastic egg in the M&Ms. It was less dense than the M&Ms so it gradually moved upward as the jar was shaken. Let's close our study with a super stumper. Did Indiana Jones fail at density? [play video] In the escape, Indy tosses the statue about 6 feet to an unscrupulous man who leaves him stranded and takes the statue for himself. Also, the sand in the bad is supposed to be equal in weight to the gold statue to prevent triggering the trap. My question: Does that look like the right amount of sand and could he have really tossed the statue? video

9 Apologia Chemistry Page 9 Work out how much sand in volume Indy really would have had to bring in there with him to replace the statue with. To make the answer something you can connect with, convert the volume in to how many 2- liter soda bottles of sand it is. Did he put enough sand in the bag and could he have tossed the statue that easily?