Kool Demo for Acid-Base Reactions

Transcription

1 Kool Demo for Acid-Base Reactions Kool Demo for Acid-Base Reactions Adapted from : Materials: Red cabbage juice indicator (Distilled) water squirt bottle 2 large (500 ml) Erlenmeyer flasks or graduated cylinders 1, 100 ml graduated cylinder 1 large watchglass Magnetic stir plate 2 magnetic stir bars 1 ringstand with large clamp Milk of Magnesia White vinegar dry ice Baking soda Sharpie marker Lab coat gloves Procedure 1. Pour 50ml indicator into both of the Erlenmeyer flasks. Label one acid and the other base. 2. Gently place a stir bar into each flask with the solution. 3. Place the base flask on the stir plate/ringstand set-up and turn on the STIR so that the solution is gently stirring (for set-up, see photo above). 4. Pour 50ml Milk of Magnesia into the 100 ml graduated cylinder. Dilute to 100ml with distilled water.

2 Kool Demo for Acid-Base Reactions 5. Slowly pour this solution into the Erlenmeyer flask with the indicator. A green color should appear quickly. 6. You can match this color to the Reference Chart for Cabbage Juice Indicator and show students that it is indeed a basic household product. 7. Take this solution off of the stir plate and replace with the acid Erlenmeyer flask. 8. Measure 50ml white vinegar to the 100 ml graduated cylinder then pour into the second Erlenmeyer with the indicator solution. Alternatively you can simply drop a small chunk of dry ice into the second Erlenmeyer flask. In this case, quickly cover with the watchglass. In either case, the solution should quickly turn red. 9. You can match this color to the Reference Chart for Cabbage Juice Indicator and show students that it is indeed an acidic household product. Now for the Grand Finale: 10. Pour the basic solution from the first Erlenmeyer into the acidic solution from the second Erlenmeyer. The solution should revert to its original purplish-red color (cabbage indicator color). 11. You can match this color to the Reference Chart for Cabbage Juice Indicator and show students that this was indeed an acid-base reaction and now the base (Milk of Magnesia) neutralized the acid (white vinegar). 12. If you have indeed achieved true neutrality, you can now wash the solution down the drain with PLENTY OF WATER TO DILUTE IT. 13. If it is not yet dilute, you can use baking soda (base) or white vinegar (acid) to add to your experiment until the original purplish-red color is achieved.

3 Kool Demo for Acid-Base Reactions Demonstration for Acid-Base Indicator Color Change Basic Substance + Acidic Substance + Indicator Indicator

4 Make Your Own Acid-Base Indicator and Then Test It! Make Your Own Acid-Base Indicator and Then Test It! Materials: Red cabbage (Distilled) water Blender Coffee filters Rubber bands 2, plastic cups (per group) 1 Spot plate (per group) Household products to test (ie. Baking soda, vinegar, ammonia, antacids, citrus juice) 1 disposable pipette (per group) 1 set of markers (per group) Filter paper Lab coats gloves Procedure: teacher 1. Peel off six big cabbage leaves and put them in a blender with 12 cups of water. Liquefy! (This can be scaled-down or scaled-up as long as the ration remains 1 leaf:2 cups water) *note: test your water beforehand.if it is not close to ph 7.0 (±0.5 ph units) then you should probably try to use distilled water. 2. Pour some of the mixture into one cup for each student group.

5 Make Your Own Acid-Base Indicator and Then Test It! Procedure: students ph is the measure of how acidic or basic a substance is. A ph indicator is a chemical that changes color based on how acidic or basic a substance is. When the indicator comes in contact with a substance, the indicator's color corresponds to that substance's approximate ph, which is a scale of zero to fourteen (with zero being the most acidic, seven being neutral, and fourteen being the most basic) that indicates the acidity or basicity of a substance. Red cabbage contains a ph indicator. You will make a solution of ph indicator and test the ph of various household products. 3. Place a coffee filter loosely over a second cup and secure with a rubber band. Carefully pour the cabbage mixture onto the filter. You should see only a deep reddish-purple liquid in the second cup with no cabbage pieces. 4. Cabbage leaves can now be discarded in trash or compost bin! Save the liquid as this is your indicator. 5. Obtain a 6 well plate. Choose six different commercial products and have your teacher put a little in each well. Write down the name of which product is in which well below. Get a variety of those from the acid group and those from the base group. 1" 2" 3" 4" 5" 6" 1" 2" 3" 4" 5" 6" Product" ph" Acid"or"Base?" 6. One at a time, pipette indicator one drop at a time until you see a color change. GENTLY swirl the plate to mix everything. 7. Write down the color of each well after adding the indicator. Use the Acid-Base Color Chart for Cabbage Juice Indicator to estimate the ph of each product and determine which are acids and which are bases.

6 Make Your Own Acid-Base Indicator and Then Test It! To make your own ph paper for easy testing on the go! 1--After you have made and strained the indicator so that only the purple liquid remains (step 3), cut filter paper into thin (3*6 cm strips) and soak it in the juice until it obtains a purplish hue when wet (depends on paper type but I soaked mine overnite for best results). 2 Remove from the juice and hang it to drip dry on a washline with clothespins. 3 When dry you can spot different samples onto it with a disposable pipette or dip the tip of the paper into a solution that you want to test.

7 The Carbon Dioxide Acid Breath Test The Carbon Dioxide Acid Breath Test adapted from: NASA, EG HQ, The Brain in Space A Teacher s Guide With Activities for Neuroscience, Raising the Level of Carbon Dioxide in Your Blood and Pipe2e) Stopper) Flask) S"r)bar) S"r)knob) S"rplate) X" Materials: Phenolphthalein or universal indicator (see ph scale/color for each indicator) Slightly basic tapwater (ph ~8) KOH (finely ground) Dry ice 2 Erlenmeyer flasks (per group) 1 Magnetic stir plate (per group) 2 magnetic stir bars (per group) 1, 2-hole rubber stopper (per group) 1, no-hole rubber stopper (per group) 1 disposable pipette (per group) 1 Normal drinking straw (per group) Sharpie marker Gloves for instructor 1 balloon (per group)

8 The Carbon Dioxide Acid Breath Test Procedure: teacher 1. Set-up each Erlenmeyer/stir plate combination as depicted above. 2. Fill each Erlenmeyer with about 20 ml of tap water (not distilled water) and drop in a stir bar. Add several drops of phenolphthalein or universal indicator to one Erlenmeyer until a slight pink color (for phenolphthalein) or green (for Universal indicator) can be seen. Quickly put on the stopper/disposable pipette combination as depicted in the picture above. Label that flask indicator only. 3. In the second Erlenmeyer, place 0.5 g of finely ground KOH, then several drops of the indicator until a slight pink color (for phenolphthalein) or green (for Universal indicator) can be detected. Quickly put on the stopper as depicted in the picture above. Label that flask indicator and absorber. Place this next to the stir plate set-up for later use. Carbon dioxide (CO 2 ) is a colorless gas. It s responsible for giving soda its fizz and plants use it for photosynthesis. We use oxygen to burn fuel for energy and CO 2 is a product of that process that we breathe out. CO 2 levels in the air are very low, however, in a closed environment such as a space shuttle, the amount of CO 2 may reach toxic levels. The level of CO 2 must be closely monitored and removed from the shuttle so that it does not poison the astronauts. In this activity, you ll learn how CO 2 can affect ph (how acidic or basic a substance is) and how to counteract this using a CO 2 absorber. Procedure: students 4. Place the Indicator Only flask on the stirplate and turn on the STIR (NOT HEAT) so that the stir bar is slowly but steadily stirring your mixture. Move the flask until the stir bar does not interfere with the pipette tip. What is the color of the liquid in the flask? Answer: pink if using phenolphthalein or green if using universal indicator 5. Take your balloon and blow it up but DO NOT TIE IT. Hold it tightly so the air does not escape. 6. Take your straw and place it over the tip of the pipette which is inserted into the stopper of your flask.

9 The Carbon Dioxide Acid Breath Test 7. Place the end of your balloon over the straw and slowly loosen your grip so that you can let the air enter into the straw. You can take turns with your own balloon. The reaction is complete when you observe a color change. Once you do you can stop. This color change alerts you that the solution has changed from slightly basic to acidic. What is the color of the liquid in the flask now? Answer: clear if using phenolphthalein or yellow to orange to red if using universal indicator 8. Now switch flasks. Turn off the stirplate. Carefully remove this flask indicator only from the stir plate and replace it with the indicator and absorber flask. What is the color of the liquid in the flask? Answer: pink if using phenolphthalein or green if using universal indicator 9. Slowly turn-on the STIR so that the solution is stirring slowly. 10. Remove the rubber stopper and USING TONGS drop a small piece of dry ice into this second flask then quickly replace the rubber stopper. 11. Watch the liquid in the flask. Do you see a color change? What is the color of the liquid in the flask? Answer: pink if using phenolphthalein or green if using universal indicator

10 The Carbon Dioxide Acid Breath Test The chemical that is responsible for the color in the flasks is called [phenolphthalein or universal indicator]. Use the chart showing the color of [phenolphthalein or universal indicator] at different ph values to fill in the ph range of each of the flasks before and after addition of CO 2. Indicator*only* CO 2 #from#your#breath# ph#range= # ph#range= # Indicator** +*absorber* Dry#ice# ph#range= # ph#range= #