Name ____________________________________
Table _____ Period _____
Describe effects of the polarity of water.
Record observations and write conclusions.
You will do these tests with your cooking group, but each person will complete, and turn in, his/her own paper.
Be sure to wash tools between tests.
Background Information
Test:
Hypothesis
Observations: r o f n t a t h
W a t c
1.
Water molecules have an uneven distribution of atoms, which is what makes them polar. Polar solutions will be attracted to a charge.
If I create a static electricity charge on a plastic water bottle, and then put the bottle next to a slow stream of water, the water will ___________
________________________________ because it is attracted by the charge of the bottle.
Charge a balloon or water bottle by rubbing it against a piece of wool, or your head. Turn a water faucet on so that there is a thin, steady stream and hold the balloon or bottle near the stream of water.
What happens?
2 . Water is polar, so its molecules are attracted to each other by hydrogen bonds.
Oil is non-polar.
If drops of a substance are dropped on a penny, then MORE drops of a polar substance will stay on without sliding off, because
_________________________________
Take a clean, dry penny. Using an eyedropper, count how many drops of water you can put on the penny before the water spills off. Observe and draw the shape of the water as you work. Dry out the eyedropper.
(Blow into it to help dry it.) Repeat the experiment using vegetable oil.
Drops of water held: ______
Draw shape that water took:
Drops of oil held: _________
Draw the shape the oil took:
Conclusions:
What does this mean in the kitchen?
Was your hypothesis correct? ____ ____
If not, explain.
____________________
____________________
____________________
____________________
Why is it important to keep electrical appliances away from water?
_______________________
_______________________
_______________________
_______________________
Was your hypothesis correct?
_______________
Explain why you say so.
____________________
____________________
____________________
____________________
Why is is important to use a liquid measuring cup, rather than a dry measuring cup when measuring water-based liquids?___________
_______________________
_______________________
_______________________

3.
Water has “surface tension” created by its polarity; detergent has a polar end, and a non-polar end.
The surface tension in water will allow you to float light objects on it. If you add soap to the water, it’s non-polar end will reduce the surface tension of the water, and the objects will _________________.
1.
Fill a clean, bowl with water.
2.
Lay a 2-3” piece of paper towel on the water, and then gently lay a paper clip on the paper so they float..
3.
Gently add a squirt of dish soap to the water and watch what happens.
4.
Try again to float a paper clip on new paper towel in the soapy water. What happens?
Describe what happened.
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
Was your hypothesis correct?
____________ If not, explain.
____________________
____________________
____________________
____________________
Adding detergent to water reduces the surface tension of the water.
Some people call this making water “wetter.” When water has less surface tension, it can get in and clean better. What are some e things you clean with water & detergent?
___________ __________
___________ __________
Polar substances will dissolve into polar solvents. Non-polar substances dissolve into non-polar solvents. Water is polar, oil is non-polar.
(Use this information to determine if sugar and salt are polar or nonpolar molecules.)
Stir these substances into 1 t of water in a bowl. Which dissolve in the water?
A pinch of salt
A pinch of sugar
Rinse and dry the bowl, and repeat the same tests in 1 t. of vegetable oil.
Describe what happened. Did the substance dissolve?
Salt in water:_________________
____________________________
Sugar in water:________________
____________________________
Salt in oil:____________________
____________________________
Sugar in oil:__________________
____________________________
According to your tests, are these molecules polar or non-polar?
Salt ________________
Sugar _______________
In cooking we often need substances to dissolve. It is essential for starting many of the chemical reactions we want.
Sometimes, though, we do not want things to dissolve. Be very careful cooking vegetables; water
–soluble vitamins can easily be lost into cooking water!
Milk is mostly water molecules (polar), but if it isn’t skim milk, it has tiny drops of fat (non-polar) floating around in it.
Watch what happens when we add detergent molecules, which have one polar end, and one nonpolar end
Put 1 T. of milk into a bowl.
Add a drop of food coloring.
Take a toothpick. Get the end of the toothpick wet, and dip it into your food coloring.
What happened when you put the toothpick with water into your food coloring? ____________________
____________________________
What happened when you put the toothpick with detergent into your food coloring? ________________
____________________________
____________________________
____________________________
The soap's polar end dissolves in water, and its nonpolar end attaches to a fat globule in the milk. The molecules of fat bend, roll, and move in all directions as the soap molecules race around to join up with the fat molecules. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops. Try adding another drop of soap to see if there's any more movement. If so, you discovered there are still more fat molecules that haven't aligned with the detergent.
We use detergent to help clean both polar and nonpolar substances.
We also use food ingredients that are polar on one end and nonpolar on the other as emulsifiers to help hold polar/nonpolar mixtures together.