Chemistry 11 Lab #17: Introducing Acids and Bases

 

Safety: Take special care when handling the chemicals in this lab.

A) Identifying acids and bases using your senses

(One should never use touch or taste to identify chemicals in a chemistry lab so the first section of this part of the lab will take place in the classroom.)

1. Note the label of each sample and do a touch and taste test to determine whether it is an acid or a base. Rinse your mouth between tests. (Acids are sour to the taste. Bases are bitter and feel slippery when rubbed between the fingers. )
2. Place a small piece of magnesium metal to see if a reaction takes place.
3. Once you have some acids and bases identified test for neutralization by mixing acids with bases to see if the properties are attenuated.
4. Use the ohmmeter to test for conductivity.

B) Identifying acids and bases using Litmus paper

1. Using the plastic dropper, half fill six four-inch test tubes with the samples from the front (make sure to label the tubes with a sheet of paper under the test tube rack. You should have one tube of each sample: hydrochloric acid, sodium hydroxide (base), lemon juice, baking soda (or cocoa if I can find dutch cocoa), vinegar and soapy water.
2. Use a glass rod to place drop of each sample on a piece of blue litmus paper and a piece of red litmus paper.
3. Note the results in the table below.
4. Save the acid and base samples for experiment C.

C) Identifying acids and bases using phenolphthalein and bromthymol blue

1. If you have done experiment B you will be using the same samples. If you have not done it you should get your samples as per B(1).
2. Retrieve a beaker of phenolphthalein and bromthymol blue with a plastic dropper in each.
3. Add a few drops of bromthymol to each of the samples and note the results in the table.
4. Save the samples for experiment B.

D) Identifying acids and bases (and finding pH) using a digital pH meter

1. Rinse the end of the pH meter in tap water.
2. Calibrate the meter using the standard solution. Rinse it again.
3. Place the meter in each of the six samples at the front and note the pH. Make sure to rinse the meter between samples.
4. Note the pH readings in the table. (pH=7 is neutral. Is a pH less than 7 an indication of acid or base? A pH greater than 7?

E) Make your own indicator (and try others)

1. Finely chop enough red cabbage to half fill a 500 mL beaker.
2. Add enough tap water to cover the cabbage and bring this to a boil with the hot plate.
3. Allow to cool, then pour the juice into a 250 mL beaker.
4. Use this mixture to test the samples in the same way as in experiment C.
5. Note the results in the table.
6. You can also do this with blackberries, beets, onions and other fruits and vegetables. If you filter the juice through filter paper and allow it to dry you can use the dried paper like the litmus paper in experiment B.

	Hydrochloric acid (HCl)	Sodium hydroxide (NaOH)	Lemon juice	Baking soda	Vinegar	Soap
Taste	Don’t do	Don’t do
Feel	Don’t do	Don’t do
Reaction w/ metal
Neutralization
Conductivity
Blue litmus
Red Litmus
Bromthymol blue
Phenolphthalein
pH meter reading
Cabbage