The Properties of Acid: Classroom Activities

Learning the properties of acid can be fun.

Today we are going to drink acid, make volcanoes, tranform grapefruits into power plants and melt some metal. This is to demostrate four properties of acids and help high school students understand the chemical principles behind these properties. Acids react with bases to form water. Acids dissociate to release extra electrons. Acids are corrosive, meaning they dissolve things by reacting with them. Acids provide a sour taste, which can be a good thing and a bad thing.

Grapefruit Battery: Acid Dissociation

The acid property behind grapefruit batteries has been understood for thousands of years.

Imagine the capability to make electricity from a piece of fruit. Because of the acid's dissociation constant, Ka, the rate at which the molecule splits into ions in water, you can make batteries out of many types of fruits and vegetables. Grapefruits work very well and are easy to prep. All that needs to be added is a copper wire and a zinc, or galvanized, nail into the juicy core. From there make the zinc nail the negative, or anode, and the copper wire the positive, or cathode, and power small amp systems like a voltmeter or Christmas light bulb.

Drinking Acid: Sourness of Acids

Drinking acid is not always a bad thing because of its sour properties.

Drinking acid is a common event, but it can tell you a lot about the acid, if you know what to pay attention to. In this activity pick four fluids that are consumable but progressively more sour. The list of carbonated water, pickle juice, milk and orange juice works well. As you drink each one rank the level of sourness for each. Once you determine a ranking from 1 to 4, compare this to the pH of each drink. The property of sourness and acid pH will be easy to see. The more sour, the lower the pH; here the soda water can vary.

Classroom Volcano: Acid-base Reacion

Acids react with bases to form water vapor similar to this geyser.

It is time to make a volcano in the classroom, but do not get too excited. This is a simple acid-base reaction between vinegar and baking soda. To perform this activity and get the best results, you need a good volcano design. To achieve this use Play-Doh and its container. Form the Play-Doh by covering the container, which should leave a hollow space that works well after shoving this back into the container. Any cup shape will work, add 2 tbsp. baking soda, and 50 ml vinegar. Watch the water vapor rise.

Melting Metal: Acids Are Corrorsive

Acids will corrode metals and other objects even at low concentrations.

Cleaning metals is very easy with this activity. To demonstrate the property of corrosion this acid activity will literally melt an atomic layer of metal off the surface, which will quickly provide a nice shiny surface once again. Take a permanent marker or oil base paint and cover the surface of a thin piece of metal. Allow it to dry well. Fill a beaker with strong sulfuric acid and carefully dip the dirty metal piece in the acid with a pair of tongs of other safe extension. With rubber gloves carefully dry the metal and notice how quickly the shine comes back.

References

• Science Buddies: Veggie Power! Making Batteries from Fruits and Vegetables
• Avogadro.Co:Acid Dissociation Constant, Ka