RELATIVE STRENGTH OF ACID SAMPLES
INTRODUCTION:
In this experiment you will determine the relative strength of acid samples, by qualitative observation of the reaction. Your unknown acid samples will be acetic acid, CH3COOH. You will react the unknowns with equal amounts of the base sodium bicarbonate, NaHCO3 .The principal product of this reaction is the gas carbon dioxide, CO2. You will trap the carbon dioxide in the balloons.
MATERIALS:
Acid unknowns:
1. 10 ml white vinegar = 100%
2. 7.5 ml white vinegar and 2.5 ml distilled water = 75%
3. 5 ml white vinegar and 5 ml distilled water = 50%
4. 2.5 ml white vinegar and 7.5 ml distilled water = 25%
Sodium Bicarbonate (baking soda)
Safety goggles
Test tube rack
10ml graduated cylinder
4 test tubes
Weighing papers
Balance
4 balloons 5" round
PROCEDURE:
This requires 2 people let someone else mark the acid samples A, B, C, and D, so you wont know which is which untill you do the experiment.
1. Check your 4 test tubes. If any have chips in the rim, exchange them for new ones. Using a pencil, mark the test tubes with the letter designation of your acid samples. ONLY USE PENCIL ON THE WHITE MARKING AREA OF GLASSWARE. Obtain 10.0 ml of each unknown acid sample and place them in the test tube marked with the matching label. Place the test tubes into the test tube rack.
2. On weighing papers, weigh-out four 2.50 g samples of sodium bicarbonate and set at lab station. Be sure to use proper procedure for the balance used.
3. One partner is to quickly dump the sodium bicarbonate sample into the first acid sample, and the other partner must quickly place a balloon over the test tube. THIS MUST BE DONE QUICKLY BECAUSE THE REACTION WILL BE VIOLENT. Hold the balloon to the rim of the test tube until the reaction is over, or the balloon will blow off. Repeat this with the other 3 acid samples.
RESULTS:
4. The gas that fills the balloons is carbon dioxide, CO2 . This is a product of the reaction. From looking at the balloons, what is the order of strength of your acid samples from strongest to weakest? How did you arrive at your conclusion?
5. How could you tell the relative strength of the acid samples from the excess sodium bicarbonate left in the test tubes after the reaction stopped?
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