Sharon Endebak

Barbie Soap

Science Concept:

Phenolphthalein, an acid-base indicator, mixes with soap, a base, to produce a pink substance.

Materials:

Arm & Hammer washing soda laundry detergent

phenolphthalein

water

latex gloves

Directions:

1. Put a couple dropper-fulls of phenolphthalein, while wearing latex gloves, on your hands, and rub together to get both hands wet.

2. Have assistant pour some washing soda on hands.

3. Rub hands together to make pink substance.

4. Have an assistant pour some vinegar unto the hands to make the pink turn back to colorless.

Introduction:

How many of you girls just love to play with Barbies? I remember when I was a little girl, I just loved to play with Barbies. Everything I owned had to be Barbie-related. Well, I even discovered how to make Barbie soap!

Explanation:

The Arm & Hammer detergent has sodium carbonate, which reacts with water to from hydroxide ions, which is a base. Phenolphthalein is an acid-base indicator. It is colorless in neutral solutions or acids. This is the situation at the start of the demonstration. When the detergent and phenolphthalein are mixed together, the phenolphthalein indicator changes color because it is in the presence of hydroxide ions, a base, from the sodium carbonate.

Detergent = Sodium carbonate = Na₂CO₃ + H₂O ---> Hydroxide ions, OH^-1

The pink color disappears if vinegar is added to neutralized the effect of the base. The phenolphthalein is colorless in the presence of acid.

Vinegar or acetic acid + Hydroxide ions ---> Acetate ions + Water

HC₂H₃O₂ + OH^-1 ----> C₂H₃O₂^-1 + H₂O

Safety:

Be sure to use latex gloves to keep hands from turning pink.

Disposal:

The soap can be disposed of down the drain.

Reference: Unknown