This experiment is for advanced students.
ACID!!! The word causes fear to creep in and get our attention.
BASIC!!! The word causes nothing to stir in most of us.
The truth is, a strong acid (pH 0-1) is dangerous, but a strong basic (pH 13-14) is just as dangerous. In this lab, we will get comfortable with the basics of bases and the acidity of acids along with how you can use both and tell the difference between them.
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Familiar acidic solutions:
- pH 1: Stomach acid
- pH 2: Lemon juice
- pH 3: Vinegar
- pH 4: Soda pop
- pH 5: Rainwater (serious acid rain could have a pH of 2-4)
- pH 6: Milk
- pH 7: Distilled water
- pH 8: Egg whites
- pH 9: Baking soda
- pH 10: Antacid
- pH 11: Ammonia
- pH 12: Limewater
- pH 13: Drano
- pH 14: Sodium hydroxide (NaOH)
Materials:
- Lemon
- Apple
- Blue litmus paper
- White vinegar
- Clear glass cup
- Tartaric acid (C4H6O6)
- Measuring spoon
- Measuring syringe
- Water
- Test tube rack
- Test tube
- Cool water
- Sodium hydroxide (NaOH) (MSDS)
- Dropper pipette
- Calcium hydroxide (CaOH) (MSDS)
- Erlenmeyer flask
- Solid rubber stopper
- Storage bottle
- Stick-on label
- Permanent marker
Acids usually taste sour and turn blue litmus paper red. There are exceptions. One exception to this is with apples. They contain malic acid. Malic acid does in fact taste sour by itself, but apples produce so much sugar that the sour taste of the acid is overpowered with sweetness. Making lemonade is a good example as well.
NaOH – Be very careful working with sodium hydroxide (NaOH). It isn’t an acid, so it shouldn’t be very harmful, right? WRONG! A strong base is just as dangerous as a strong acid. Please be careful when using them.
Don’t get confused and don’t forget what litmus paper indications mean. Acids turn blue litmus paper red, and bases turn red litmus paper blue. If you are testing a substance and the paper doesn’t change color, try the other type. The substance might not be neutral, but an acid or base that you used the wrong color litmus paper.
When testing with litmus paper, don’t dip the litmus paper into the chemical bottle. Use a clean dropper to transfer the chemical to the paper. Dipping into the chemical can and will, eventually, contaminate the chemical.
When shaking a liquid in a test tube or flask, put a solid rubber stopper on top. If you just start shaking from there, your stopper may fly across the room and scare your dog unnecessarily. The hot, or acidic, or basic contents of the container will find a place on the salad waiting to be served. The paramedics will be puzzled when they find the entire family, heads down, lettuce hanging from their mouths. With the stopper firmly inserted, wrap your hand around the container with your thumb over the stopper, pushing down to hold it in place while you shake.
After we finish the experiment, don’t discard the contents of the Erlenmeyer flask. It now contains limewater, a substance that we want to save for later experiments. Carefully pour the liquid into a storage bottle and discard the solids in the trash. Place a sticker on the bottle and/or use a permanent marker to label the bottle for future use. Keep the storage bottle out of direct sunlight when storing it.
We will explore for ourselves some of the properties of acids and bases. If we consider the acid-base theory discussed below, it will help us to further understand what we are experiencing in our lab.
C3000: Experiments
Download Student Worksheet & Exercises
Cleanup: We must clean everything thoroughly after we finish with the lab. After cleaning with soap and water, we need to rinse everything thoroughly. Chemists use the rule of “three” in cleaning glassware and tools. After washing, chemists rinse out all visible soap and then rinse three times more.
Storage: Place cleaned tools and glassware in their respective storage places.
Disposal: Liquids can be washed down the drain, and solids put in the trash.
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