Last updated 10-1-07
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Experiment #10: Preparing Red Cabbage Extract

Let's begin with the items that you will need for the lab that you may need to buy at the grocery store. There are three items.

#1. Distilled water: This is not the same as bottled drinking water. Distilled water is made from steam that is cooled and collected. It is supposed to be free of any salts (minerals). An alternative to distilled water is deionized water. Deionized water is water that has been passed through resins that capture all dissolved salts. You use these to rinse off glassware so there are no mineral spots. It is also used where you want pure water.
#2. Red Cabbage: You will also need red cabbage. The pigment in red cabbage is known for its ability to change colors depending on the pH (level of acidity) that it comes in contact with. In this experiment, you will extract the pigment from the cabbage. This extract will be used in future experiments to test the pH of liquids.

#3: Isopropyl alcohol. This is used as a preservative for the cabbage extract and for washing out used test tubes. If you rinse them out with rubbing alcohol, it makes them dry faster. Isopropyl alcohol at 70% concentration is called rubbing alcohol. If you find isopropyl alcohol at a higher percent, like 90%, get that.

 
The below items are in your kit. You can buy them at the grocery store, but again, these are in your kit.

#4: Baking Soda: Baking soda when mixed in water will make it alkaline (also called basic), which means it is the opposite of acid. (explained more farther down). It will also be used to test the red cabbage extract.
#3. Vinegar or lemon juice:Vinegar or lemon is needed to check how the red cabbage extract responds to an acid. If you do get vinegar, get one that is clear. This white distilled vinegar is clear. You will using vinegar for later experiments.
The following items should be in your chemistry kit.

#6. A few empty test tubes: You will use these to collect purified water and the red cabbage extract.

#7. Two plastic dropper bottles. One labeled pH Indicator (cabbage extract) and the other label Purified Water. In this experiment, we will be extracting the red pigment from the cabbage and placing it in the pH indicator bottle. Both bottles have a nozzle in them. Just like the Purified water bottle, the pH indicator bottle may need a spatula or fingernail to get the nozzle out of the bottle.

#8. Funnel. Your kit has a funnel and you might still have the small plastic tube still connected to it from the last experiment. You can pull off the plastic connector because it will be easier for the funnel to fit into the test tube without it.

 
#9. Plastic pipette. This pipette comes with a built-in dropper. Normally this pipette is used to draw up liquids into the bulb at the top and then squeeze out the liquid into some other container. For this lab we will mostly use its long thin portion as a plunger.
Instructions for experiment 2 of lab: Creating extract of red cabbage
You can either tear off leaves from the cabbage and tear them into smaller pieces or you can cut about 1/3 of a cabbage and cut the leaves into smaller pieces. They don't need to be as small as shown here.
Fill the larger beaker with about 150 milliliters of distilled water. Place the water into a small pan. This can be either a metal or cooking glass pan.
Place the torn (or cut up) pieces of red cabbage into the pan with the water. Turn the heat up to medium or medium high. (You can try this in the microwave if you wish. You just got to get the water to boil.)
Once the water starts to boil, turn down the heat so it boils gently.

If it looks like there's not enough water to cover the leaves, or too much of the water is boiling way, add a little more of the distilled water. (Perhaps another 50 mL)

Keep it at a gentle boil for about 10 minutes, or until the water turns a purple color. Then turn off the heat and let it cool down.

(Take a picture at this point. See if you can set your camera to either 1600x1200, 1280x960, or 1024x768. If you own a 2 megapixel camera, just use the highest setting [3 stars].)

While the cabbage is cooling, get a piece of filter paper out of the jar in your kit.

Fold the paper in half.
Fold it again, but this time not quite in half. Leave a little overlap like shown. This will help the filter paper sit snug into the funnel.

Open the filter paper so just one half side is opened.
Place the filter paper into the funnel and place of few drops of your purified water onto the filter paper to help hold it into place. The funnel will sit in an empty test tube. If the the short plastic connector tube is still on the funnel, remove it.
Once the cabbage cools down, pour the cabbage extract liquid into your 250 ml beaker. Also, put a plate under the beaker so if some juice spills, the plate will catch it. The cabbage juice might stain cabinet tops, clothes, and other fabrics.

Pour the cabbage extract (juice) into the funnel with the filter paper. The liquid will go through fairly fast. When the liquid starts to fill up the test tube, move the funnel over to an empty test tube right next to it.

Again, because something might spill, I have the test tray sitting on a plate (or something like it) to catch any of the purple cabbage extract.
Here I'm using a saucer as a coaster for the beaker to again keep any liquid from staining a table or counter top.
As one test tube starts to get full of the filtered cabbage extract, empty it into the pH indicator bottle. The funnel should be now sitting in a second test tube filtering liquid into that test tube. When that starts to get full, place funnel back into the first test tube. It takes about 5 or 6 test tubes to fill the pH indicator bottle. If you have extra cabbage juice (extract) you can rinse the extra down the sink.
Either before putting the extract into the pH indicator bottle or before the bottle is full, you need to add some isopropyl alcohol to the extract. Do this by first pouring about 10 mL of isopropyl alcohol into the small beaker and then use the plastic pipette to transfer the alcohol to the bottle. The alcohol should take up about 1/8 of the volume of the bottle. This will make an alcohol concentration of about 10%, which should be enough to keep the extract from spoiling due to bacterial growth. The alcohol should not affect the pH or color.

Just like the purified water bottle, the pH indicator (cabbage extract) bottle needs the nozzle replaced and the cap placed on it.


Take a picture of your pH indicator solution made of cabbage extract. Hold it so your face is visible too.
Section 2: Checking cabbage extract for use as a pH indicator.

Red cabbage extract changes to many colors depending on acidity. Acidity is measured on a pH scale. pH stands for "potential for Hydrogen." Acidity is caused by hydrogen atoms that have lost their electrons and are roaming free in water [H+]. The scale goes from 0 to 14. The fractions represent the concentration of these positively charged hydrogen atoms [H+]. You can probably see the pattern. The numbers of the pH scale represent the number of zeros behind the 1. In other words, they are exponents. For example, 7 means or 10x10x10x10x10x10x10 or 10,000,000. Pure water has a pH of 7 because it has an acid [H+] concentration of one over ten million. pH 3 has a concentration of one thousandth. One thousandth is a larger number than one ten millionth. Therefore the smaller the pH numbers the greater the acid [H+] concentration.

The opposite of acidic is alkaline (or basic). Alkaline gets its name from the "al kali" plant whose ashes are capable of neutralizing acids. It does this because it contains KOH. The "OH" is called hydroxide and as the equation shows, it combines with the acid [H+] to form water.

At the end of this experiment you will be comparing the colors of three test tubes. The left will have vinegar. The middle will have distilled water. The right will have baking soda in water. All three will have 3 drops of the red cabbage extract added to them. By looking at the color chart above, it shows the vinegar is in the 1 to 3 range. The distilled water is about 7 (as it should be) and the baking soda is around 10 meaning it is alkaline.

When solutions are alkaline, the [OH-] concentration is larger than the [H+] concentration. Water is neutral because the acid [H+] concentration is equal to the [OH-] concentration. Also, both of these are at very low concentrations (one ten millionth)
Pour a little distilled water into the small beaker. Less than 10 ml is fine. We could use our purified water that we made in the previous experiment, but for this test the distilled water should be adequate.
Pour it into an empty test tube. Only fill the test tube to about 1/4 full. Place the test tube back on the test tube rack.
Use your microspatula and scoop up a little baking soda and place in an empty test tube
Pour some of the distilled water into the test tube. Shake it to get some of the baking powder to dissolve.  Not all of it needs to dissolve.

You can use white vinegar or lemon juice to check to see if your red cabbage extract really works.

Pour a little vinegar into the small 50mL beaker. 10 ml or less is plenty. You will only need about 3 ml to fill a test tube 1/4 of the way.

You pour into the beaker first because it has a small pouring spout, which makes it easier to pour into the test tube.

Pour some vinegar into an empty test tube. Fill the test tube to about 1/4 full. Make a note which test tube has water and which has the vinegar. You can use the small paper labels in your kit if you want.

Place three drops of the red cabbage extract into each test tube. (if extra drop goes in, it's OK) The tubes with vinegar, water, and baking soda don't have to be in this order, but when they are, the acidic one is on the left, the neutral is in the middle and the basic (alkaline) one is on the right; which is the way the pH color scale is laid out.

After placing the drops in, you will need to pick up each test tube and swirl the liquid to get it to mix. Placing a sheet of white paper behind the test tubes will help the colors stand out.

After adding the our red cabbage pH indicator drops, you should have something similar to the below picture. (Take picture of your 3 test tubes.)
CLEAN UP
You can pour out the contents of the test tubes into the sink.
Rinse with tap water first.

Pour some distilled water in the beaker (if it had vinegar in it, rinse it first a couple of times). Use the beaker to pour some distilled water into the tubes to rinse out the tap water.
If you do a final rinse with the isopropyl alcohol, the test tubes will dry faster.
Place test tubes upside down in the test tube tray to allow them to drain and dry. The test tube lids can be placed in the tray as well so as not to lose them.
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Since Feb 23, 2004