Sharon Endebak

Lemon Shell Game

Science Concept:

How a lemon reacts with acids and bases.

Materials:

water

1 M sodium hydroxide (NaOH)

phenolphthalein

3 lemons

knife

syringe with no tip or plastic tip

50 mL beaker

Directions:

1. Mix 10 mL of the 1.0 M sodium hydroxide with 90 mL of water to make 0.1M

NaOH.

2. Pour 5 mL of the 0.1 M sodium hydroxide/water solution into 50 mL beaker.

3. Add four drops of phenolphthalein into beaker.

4. Use the syringe to suck up 2-3 ml the pink basic solution from the beaker.

5. In just one of the lemons make a tiny hole for the syringe to go through.

6. Inject the pink basic solution into the lemon.

7. Mix lemons around, and have kids try to guess which is the pink lemon.

8. Then cut open the lemons to find the pink one.

9. After, squirt some pink NaOH on open lemon to show how pink disappears.

Introduction:

Let's play a game now. All of these lemons look similar, right? Well, I am going to give just one of these lemons a shot of this pink solution. Now, I am going to mix them around and see if you can guess which one is the pink lemon.

Explanation:

When the sodium hydroxide, which is a base, is mixed with phenolphthalein, it turns pink. When the base is neutralized by the acid, citric acid, which is present in lemons, the pink solution turns colorless. This happens because the base is neutralized in an acid solution, which causes the indicator to become colorless. All of the base is neutralized by the citric acid. The inside of the lemon stays acid so the phenolphthalein indicator is colorless.

NaOH + phenolphthalein ----> pink colored solution

neutralization: 3 NaOH + H₃-citric acid -----> 3 HOH + Na₃(citrate)

Safety:

Use caution using the knife to cut the lemons open. Use a plastic syringe without the needle.

Disposal:

The lemons can be disposed of in the garbage, and the remaining solution can be disposed of in the sink.

Reference: Unknown