Linette Guare

The Magic Pitcher

Concept: The concept of acids and bases are taking place.

Materials:

• Opaque pitcher or large beaker covered with foil
• four - 250 mL beakers
• 400 mL water
• phenolphthalein
• vinegar
• sodium hydroxide 0.1M (NaOH) first choice; (or household ammonia (smells bad).
• 3 - eye droppers

Pre-Demo Directions:

1. Label the beaker 1 - 4.

2. In beakers 1 & 3, put 30 drops of phenolphthalein.

3. In beaker 4, put 45 drops of vinegar.

4. In the pitcher, put 15 drops of sodium hydroxide or household ammonia and 400 mL of water.

Directions:

1. Pour 100 mL of water from the pitcher into each four beakers.

Beakers 1 & 3 should be pink, and beakers 2 & 4 should be colorless.

2. Pour the liquids from beakers 1, 2, and 3 back into the pitcher (not beaker 4 at this time).
Ask the students what color do they think is in the pitcher?

3. Pour the liquid from the pitcher back into beakers 1, 2, and 3. Now all three should be pink.

4. Now pour the liquid from all FOUR beakers back into the pitcher. Ask the students what color do they think is in the pitcher? Why does the last beaker change the color from pink to colorless?

5. Pour the liquid from the pitcher back into the four beakers. All four should be colorless.

Introduction:

I was thirsty the other day and I went to get a drink from this pitcher, but every time I poured a glass I got a different drink. (Start experiment.) Sometimes I got pink lemonade and sometimes I got water. The pitcher can't make up it's mind.

Explanation:

Phenolphthalein is an indicator of acids and bases. In an acid, its colorless. In a base, it's pink. Sodium hydroxide or ammonia is a base, and it was in the pitcher, so when added to the phenolphthalein in beakers 1 and 3, it turned pink. The two so far (1 & 3) beakers so far had ammonia, a base and the phenolphthalein which is pink.

The second beaker has only the ammonia but no phenolphthalein, so it remained colorless. So the first three beakers poured back into the pitcher give a pink solution, which is then when poured back into the first three beakers as a pink solution. In the fourth beaker, a strange thing happens in that the pink solution coming out of the pitcher now changes to colorless. This happens because the 4th beaker contains some vinegar or acetic acid which neutralizes the ammonia, changes the solution from basic to acidic. Under acidic conditions, the phenolphthalein indicator is colorless.

For the final event, pour of all four of the beaker back into the pitcher. Vinegar, which is acidic, which was in beaker 4, turned everything colorless, because acid neutralized the sodium hydroxide or ammonia base (NH4OH).

Neutralization: HC2H3O2 + NaOH ----------> Na(C2H3O2) + H2O

Safety Precautions: Wear goggles and be careful not to splash the bases in your eyes.

Waste Disposal: Pour the liquids down the drain.

Reference: Unknown