Physical Experiments

Purification of ethanol

Ethanol has a boiling point of 78.37 °C, while water has a boiling point of 100°C. This means ethanol will evaporate more quickly than water. The flask containing the mixture of ethanol and water should be heated under water (water bath) , to ensure that the flask’s temperature will increase evenly and gradually and not above 100°C, so in the flask, water will hardly boil together with ethanol, contaminating the ethanol vapor.  The ethanol vapor is then collected in the glass tube, around which cold water is circulated to cool it down. In the end, the vapor condenses and flows into the target container.

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Freezing

Water’s freezing point is 0 °C while ethanol’s is -114°C, so it’s a good method to put the mixture of water and ethanol into the freezer. Some days later, the water in the liquid will freeze into ice. After removing the ice, the mixture will contain a higher ethanol concentration. 

 

“Salt out”

Alcohol and water can form homogeneous mixtures because they can form hydrogen bonds with each other. However, ionic compounds, like salt, are composed of electrically charged ions, which have a greater ability to be attached to water molecules. As a result, if we add salt to the mixture of ethanol and water, the water molecules will rather bond to salt instead of ethanol, making ethanol separate from the mixture, like oil. Its density is less than water, so it will float on top of water, and can be extracted using a syringe or spoon.

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Proof of why washing hands is still the most effective

1. First, fill a container with water.

2. Then sprinkle grounded pepper (or other light powder that is not soluble in water) on it.

3. Stick your finger into the water. You’ ll see that some pepper powder goes on your finger. 

4. Now cover your finger with soap and dip your finger into water again.

5. Pepper powder will scatter around your finger as if they are afraid of the soap.

The reason for this is that the surface tension of soap is much less than that of water, so the water molecules will be pulled towards places with higher surface tension, carrying the pepper powder with them. This is also why washing hands with soap is one of the most effective precautions against the virus or other diseases. 
 

Holding fire (Adults only)

1. Put some hand sanitizer on your hand.

2. Ignite it.

The alcohol in the hand sanitizer will start to burn, generating a bluish flame. Your hand does not feel the heat, because hand sanitizers also contain water. Water has a high specific heat capacity and will absorb the heat of combustion, while its temperature increases slowly.