To introduce reactions between acids and bases with a strong visible result.
Materials:
4L beaker
600mL beaker
Long stirring rod
Large tray
Reagents:
0.5% Methyl orange solution
3M Hydrochloric acid
Alconox powdered soap
Sodium bicarbonate (NaHCO3)
Hazards and PPE:
Hydrochloric acid is acutely corrosive and toxic. Avoid skin contact and inhalation of fumes.
Methyl orange is toxic if ingested. Handle with care.
Wear approved safety goggles and gloves.
Protocol:
Preparatiom
Place a very large tray on the demonstration bench.
Add 600mL DI H2O to the 4L beaker.
Add 100g NaHCO3 and 100g Alconox soap to the 4L beaker.
Prepare ~550mL 3M HCl in a 600mL beaker.
Stir solution with a stirring rod. All of the solid may not dissolve.
Demonstration
Pour 200mL 0.5% methyl orange solution into the 4L beaker. Solution should look similar to orange juice.
Place the 4L beaker on the center of the large tray.
Quickly and carefully add all of the 3M HCl in one pour to the 4L beaker and stand back.
The mixture will immediately erupt out of the beaker. A color change will occur and the mixture will take on the appearance of a strawberry float.
After some time, parts of the solution will turn yellow.
Disposal:
End mixture can be disposed of down the drain with excess amounts of water.
Reactions:
HCl(aq) + NaHCO3(aq) → NaCl(aq) + CO2(g) + H2O(l)
The soap added to the solution serves only the presentation purpose of making it foamy, and does not contribute materially to the reaction taking place.
Acid-base indicators such as methyl orange change over a certain color range with the change in pH. Methyl orange turns from a yellow-orange color at pH =4.4 to a red color at pH = 3.
The high indicator concentration creates the deep orange color in the basic solution and a berry red color in the end solution.
