We began by asking the question, what is density? Density is a measurement of mass, or the relative heaviness of an object with a constant volume. Simply put, density is a measure of how much "stuff" is in something. That "stuff" pertains to atoms and molecules, which make up the mass of an object. For example, in a liquid, the molecules are loosely "hanging out". Kat and I demonstrate this by clasping our hands closely together, and wiggling our fingers around to demonstrate the "hanging out" of liquid molecules. Some liquids are denser than others, which means that their atoms are "hanging out" closer together, they're more tightly packed, but not quite as tightly packed as they are in a solid. Things that are really dense, are generally heavier than those that are not.
To demonstrate the density of water, and how it can change, Kat and I did a floating egg demonstration.
2 tall cups/glasses
We took 2 12 oz glasses and filled them both with water. In one of them, Kat added 7 Tbsp of salt and stirred until the salt was mostly dissolved. Kat and I each took an egg and dropped it into a cup. Predictably, the egg sank in the cup with water and floated in the cup with the added salt.
|The difference in the density of these liquids is quite clear.|
Now that we had demonstrated how to give water a different density, it was time to conduct an experiment!
Wen we added the salt, it made the water more dense, thus it heavier than the egg. This allowed the egg to rise to the surface. It seemed reasonable to suppose that we could dissolve other substances in the water, and we would get the same result. I knew that salt allowed for greater buoyancy, but what if we added sugar instead?
We decided to test it out, by adding a third cup with 7 Tbsp of sugar added to the water. Sure enough, it worked, and the egg was floating!
|Today we learned that dissolved sugar yielded just as much buoyancy as salt!|
Next time we do this, we'll try dissolving other solids in the water, to see if it truly is the case that dissolving any solid (that is safe to use, and that we have at home) in water will make it more dense and cause the egg to float. For now, sugar worked, we learned something new, and now we were off to our next demonstration....
Making a liquid rainbow!
|Ta~Da! We're going to make a rainbow in a glass!|
50 mL (1/4 c) dark liquid corn syrup, honey, or boiled sugar water*
50 mL (1/4 c) liquid dish soap
50 mL (1/4 c) water
50 mL (1/4 c) vegetable oil
50 mL (1/4 c) rubbing alcohol
Tall 12 oz clear glass/cup
* We didn't have corn syrup or honey on hand. Instead, we made a sugar water mixture by bringing 1/2 cup of water to a boil and slowly dissolving 1 1/2 cups of sugar, stirring constantly. We let it cool to a warm temperature, and used an extra cup to mix in some food coloring.
Pour your liquids into your plastic cups (keeping them separate). Mix desired food coloring into each cup.
When you're ready to start pouring your density column, add the liquids in the following order. Make sure to pour very slowly! Tilt the cups to the side so that the liquids travel down the side of your glass.
1. Add the syrup/honey to the 12 oz. glass.
2. Slowly pour dish soap over the syrup.
3. Slowly pour water over the soap.
5. Slowly pour your vegetable oil over the water.
6. Slowly pour the rubbing alcohol over the vegetable oil.
|If you pour carefully, this is what you'll end up with!|
We admired our beautiful liquid rainbow, and talked a little more about density. This is a great way to illustrate exactly what density means in relation to other liquids. Kat and I talked about which liquid was heaviest, why that might be, and what it might be like if the water we are used to on Earth were more like some of these other liquids (what it would it be like if rain was the consistency of vegetable oil?). It was really neat to see how all of these liquids were so alike, yet completely different.
All this talk about properties of matter got me thinking. What about surface tension? Do all liquids have it? Let's find out!
4 small cups
3 other liquids - try to have a nice variety of liquids (we used half and half, vinegar, and olive oil)
piece of paper for recording your predictions and observations
We took 4 small glasses and filled them with the following liquids: water, half and half, vinegar, and olive oil. We placed a penny in front of each glass. I had Kat make a prediction of how many drops of each liquid we could fit on a penny. She thought that the penny could hold 11 drops of water, 7 drops of half and half, 8 drops of vinegar, and 10 drops of olive oil.
We set to work. Kat used the medicine dropper to place water droplets on the penny. She got to 26 drops before the surface tension broke and the water spilled! She moved on to the half and half, which took 25 drops. The vinegar gave 26 drops and the olive oil gave 18. Why did the olive oil have such a low number compared with the rest of the liquids? At first, I thought it was because oil was denser than the other liquids. However, Kat poured the rest of the liquids into the oil, and I was quickly proven wrong. After searching for the answer online, we found out that oil has less surface tension than water, which explained the amount of drops it took before the oil spilled over.
Once we had our answer, Kat was able to play with the liquids as she saw fit. Can you guess what happens when you combine vinegar with half and half? This time, the reaction took place under a layer of olive oil, and it was really neat to see!
|Do not break the seal! This will smell terrible. When cleaning, keep your nose far away from this glass!|
All in all, today was filled with great demonstrations and experiments pertaining to different properties of matter! We learned quite a lot about density, and about surface tension. These demonstrations made the concept of density, matter, and mass, much easier to grasp, and I think Kat will have a better understanding of it as well, as she heads forward in her life of discovery!