In the last few weeks, we have conducted various experiments that use vinegar. Two weeks ago, you made dirty old pennies shine like new (http://discoveryexpress.weebly.com/homeblog/a-simple-solution-to-your-dirty-pennies), and last week, you created a film canister rocket (http://discoveryexpress.weebly.com/homeblog/make-your-own-film-canister-rocket) using either antacid or vinegar and baking soda for fuel! If you did either of those experiments, you know that vinegar is acidic. That is what allows it to react with other basic substances such as baking soda.
To learn more about acid-base reactions, check out this blog: http://discoveryexpress.weebly.com/homeblog/experimenting-with-eggs-acid-base-reactions-and-osmosis
Today, you are going to use vinegar in two different experiments that show how vinegar can react with calcium. In the first experiment, you will create plastic out of milk. Sound crazy? Let’s find out more.
Okay, there isn’t ACTUALLY plastic in your milk. The chunks that you see in the image above are a substance called casein. Casein is found naturally in any mammal’s milk. The word casein comes from the latin word caseus, which means cheese. The cow milk that you drink has protein, and 80% of that protein comes from casein. Casein also contains the calcium that you get from drinking milk.
At the end of your activity, your result will look something like this:
You don’t usually encounter chunks of casein in your milk. How will you end up with this result? As you know, the acid in vinegar reacts with other substances such as calcium. In the following activity when you mix vinegar with milk, the casein protein in the milk refuses to mix with the acid in the vinegar. Thus, you are left with blobs of casein that will harden into a plastic-like substance.
YOU WILL NEED:
- Sauce pan
- Adult help
Here’s what to do!
- Measure one cup of milk and add it to the sauce pan. Have an adult help you heat up the milk until it is hot, but not boiling. Watch the milk carefully so it does not boil!
- Once the milk is hot, carefully pour it into the bowl.
- Use a teaspoon to add four teaspoons of vinegar to the hot milk.
- Use a spoon to stir the vinegar milk mixture for one minute.
- Predict: What do you think the vinegar has done to the milk? What will happen when you pour the milk through the strainer? Write your predictions down in your observation notebook.
- Place a strainer in the sink and pour the vinegar milk mixture through the strainer. What do you see? Take pictures, sketch what you see, and write down your observations in your observation notebook.
- You should have seen a bunch of weird blobs left in the strainer. Once these blobs cool off, rinse them off in cool water and press them together. Now you can form them into any shape you want and it will harden into a plastic-like material in a few days!
- What is casein?
- What were the blobs left over after you dumped the vinegar milk mixture through the strainer?
- Why were those blobs created?
- Is there actually plastic in milk? If not, what is it?
Extension: If you want to make this activity into an experiment, try some of the following ideas!
- Use another acidic substance to see if it works better or worse than vinegar.
- Alter the amount of vinegar to see if it creates more or less casein blobs.
- Use different kinds of milk to see if all milk has the same amount of casein.
In the next experiment, you will use vinegar to break down the calcium in a chicken bone. A once solid bone will become bendy and flexible. Why does this happen?
Predict: Why would vinegar make a bone flexible?
When you leave a bone in vinegar, a reaction happens! The acid in the vinegar is strong enough to eat away the calcium in the bone over time. You may have seen this same reaction happen when you dissolved eggshells (http://discoveryexpress.weebly.com/homeblog/experimenting-with-eggs-acid-base-reactions-and-osmosis).
As you’ve probably heard from your mother, calcium keeps your bones strong! That calcium is what keeps your bones from bending or easily breaking. Once that calcium is removed, there is nothing to keep the bone rigid and strong. Of course, the calcium doesn’t just disappear; the acid in the vinegar frees the calcium from the bone and it becomes dissolvable in water. The once hydrophobic (water-fearing) calcium becomes hydrophilic (water-loving). Once this happens, all that is left is the flexible tissue that makes up the bone. Now you know why it’s important to drink your milk! (Or at least get some good source of calcium in your diet!)
Now that you understand how vinegar breaks down calcium, try it out for yourself!
YOU WILL NEED:
- Chicken bone
- Tall glass or jar
Here’s what to do!
- Whenever you have chicken, save a leg bone. (Other bones will work, but the leg bone is nice and rigid to start out with).
- Remove any remaining meat or skin from the bone and rinse it off in the sink.
- Record observations about the bone in your observation notebook. What does the bone feel like? Can you bend it at all?
- Put the bone in a tall glass or jar. Dump vinegar into the container until it completely covers the bone. No part of the bone should be sticking out of the vinegar.
- Cover the glass or jar and leave it to sit for 3 days.
- Times up! Dump out the vinegar and remove the bone from the container. How has it changed? Record your observations in your notebook and compare the bone now to how it was three days ago.
- Did the bone really turn into rubber? Of course not! What happened to it?
- Why would vinegar change the quality of the bone?
- What kind of reaction occurred?
- Do you think other acids would work the same way as vinegar? What if you put the bone in orange juice?
- Would thicker bones take longer to become bendy? Would smaller bones become bendy sooner?
- If you put the leg bone back in vinegar, will it become even more bendy? Does time spent in vinegar affect the bendiness of the bone?