concept of a catalyst is fundamental to chemical reactions but
not applied very much in introductory classes. In fact, the term
catalyst is probably more commonly used by the general
public than the chemistry teacher. The problem is simple, a catalyst
is relatively uncommon at the general chemistry level.
There are a few common applications, like the decomposition of
hydrogen peroxide in the presence of manganese dioxide. This decomposition
can also be related to the bubbling observed when hydrogen peroxide
is used to clean a minor wound. But it is difficult to see how
either of these examples illustrates the definition appearing
in most textbooks. Most books give a definition similar to "a
catalyst is a substance that greatly accelerates the rate of a
chemical reaction without itself being permanently changed". The
part about increasing the rate of the reaction is easy but the
rest of the definition is elusive.
is a great reaction available that demonstrates the full action
of a catalyst using readily available chemicals. I can certainly
recommend it even for general chemistry classes.
- 250 ml beaker
- Laboratory grade thermometer (110oC)
- Laboratory burner
- Ring stand, iron ring, and wire gauze
- Glass stirring rod
- Graduated cylinder
- 0.2 g laboratory grade cobalt(II) chloride, CoCl2 dissolved in 5 mL water
- 20 mL 6% hydrogen peroxide
g sodium potassium tartrate, NaKC4H4O6 (also called Rochelle's
- Large tray to contain the setup
The chemical equation for the reaction is:
H2O2(aq) + NaKC4H4O6(aq)
→ 4 CO2(g) + NaOH(aq) +
KOH(aq) + 6 H2O(aq)
Dissolve the 5 g of NaKC4H4O6 in 60 mL of deionized (or distilled) water in the 250 mL beaker then pour in the 20 mL of 6% H2O2. Place the beaker on the ring stand and heat to 70oC. Observe the very slow rate of the reaction at this temperature then remove the burner and shut off the flame.
Now add the pink catalyst solution (0.2 g CoCl2 dissolved in 20 mL of water). Stir once or twice and stand back. Observe the pink color of the Co+2 disappear and a green solution form with CO2 gas being evolved very rapidly. Have the setup sitting in the tray since the effervescence may cause some of the solution to overflow the beaker. The evolution of CO2 gas ceases after about 30 seconds and the original pink color of the Co+2 ion reappears. The temporary appearance of the green color allows you to discuss the possibility of an intermediate species or activated complex.
This demonstration is easy to run and very impressive to see. It is certain to open the door to a lively discussion and change the topic of a catalyst from a dull definition to an exciting concept.