Cody Svoboda

Rainbow in a Cylinder

Science Concept: A chemical reaction takes place to produce carbon dioxide and an acid to change the color of an indicator.

Material:

• 1 Alka Seltzer Tablet (Broken)
• 4 mL. Universal Indicator
• 0.1 M NaOH (17 mL. Of diluted (6 M) sodium hydroxide, diluted to 600 mL. With distilled water. (Mix this ahead of time and save extra for later).)
• 250 mL. Graduated Cylinder
• 250 mL. Distilled water
• Small amount of Vinegar

Directions:

• Put the Universal Indicator into the cylinder
• Add 75 mL. of the 0.1 M Sodium Hydroxide into the cylinder
• Fill the rest of the cylinder with water to 250 mark
• Drop the Alka Seltzer into the cylinder
• Add a small amount of vinegar to the top of the cylinder to create a red color

Introduction: I love rainbows. Do you? All the colors are so beautiful, but it seems like they hardly ever happen. I thought to myself that it would be so cool if I could create a rainbow whenever I wanted to. So today I want to show you what I have finally come up with.

Explanation: The universal indicator added to the sodium hydroxide turns the original solution a violet color. The indicator is used to detect the presence of an acid or base, and the sodium hydroxide is a base, turning the solution purple. The Alka-Seltzer tablet contains sodium bicarbonate and citric acid. When this tablet hits the water, it dissolves and makes carbon dioxide bubbles.

When carbon dioxide comes in contact with water, it makes carbonic acid. The carbonic acid neutralize the sodium hydroxide base. The increasing presence of an acid, therefore, causes the universal indicator to change colors based upon the acidity of the solution. As the solution neutralizes, the base concentration decreases, while the acid concentration increases. The process of color changes occurs as the solution becomes more and more acidic, causing blue, green, and yellow colors to form. The acidic solution created by the Alka-Seltzer tablet is not strong enough to make a red color, however, so vinegar is added to increase the acidity and turn the indicator red at the end of the demo.

CO2 + H2O ---> H2CO3

Neutralization: H2CO3 + 2 NaOH ---> Na2CO3 + 2 H2O

Waste Disposal: This solution is safe to be put down the sink. There is nothing in it to damage the drain of the sink.

Safety:

-When dealing with the solution always wear goggles. This is a protection in case any splashes up.

-When adding Alka Seltzer the solution, watch out. It might bubble over causing a mess and a possible danger.

Reference: Charles Ophardt, Professor of Chemistry, Elmhurst College, 2000.