Involvement of catalysts in reactions
Catalysts provide an alternative route for reactions to proceed. They are involved in the progress of the reaction. This reaction involves the oxidation of potassium sodium tartrate by hydrogen peroxide using a cobalt salt as a catalyst. This is an exciting and spectacular reaction.
Read our standard health & safety guidance
Apparatus and chemicals
Eye protection
Each group of students requires:
Beaker (250 cm3)
Measuring cylinder (50 cm3)
Measuring cylinder (10 cm3)
Tripod
Gauze
Bunsen burner
Thermometer, 10 oC – 110 oC
Access to balance (1 d.p.)
Potassium sodium tartrate (Rochelle salt)
Hydrogen peroxide (20 volume) (Irritant at this concentration) (see note 1)
Cobalt(ll) chloride solution, 4% (Toxic) (see note 2)
Distilled water
Technical notes
Potassium sodium tartrate (Rochelle salt) (Low hazard) Refer to CLEAPSS Hazcard 36C
Hydrogen peroxide (20 volume) (Irritant) Refer to CLEAPSS Hazcard 50 and Recipe card 32
Cobalt(ll) chloride solution, 4% (Toxic) Refer to CLEAPSS Hazcard 25 and Recipe card 71
1 For 20 volume hydrogen peroxide solution, it is best to use freshly diluted 100 volume hydrogen peroxide (Harmful), as the concentration of old samples decreases over time, and hence the rate decreases.
2 The cobalt(ll) chloride solution should be made in distilled water (4 g in 100 cm3 of water).
Procedure
HEALTH & SAFETY: Wear eye protection
a Weigh 4 g of the potassium sodium tartrate into a 250 cm3 beaker. Add 50cm3 of distilled water. Put the beaker on the tripod and gauze.
b Heat the mixture in the beaker to about 80 °C, stir to dissolve the solid.
c Add 20 cm3 of 20 volume hydrogen peroxide solution to the solution in the beaker. Check the temperature, warm to 80 °C if necessary. Note any signs of reaction.
d Add 5 cm3 of cobalt(ll) chloride solution to the mixture in the beaker. Take care to avoid skin contact. Note any colour changes and gas produced.
Teaching notes
It is worthwhile trying this experiment before carrying out in class, because it is important to note the colour changes that occur when carbon dioxide gas is evolved.
This is an impressive demonstration of how a catalyst is involved in the progress of a reaction. Students can add another 10 cm3 of the hydrogen peroxide solution and if there is any potassium sodium tartrate remaining they will see a similar reaction.
The reaction is an oxidation of the tartrate ion (proper name is 2, 3-dihydroxybutandioate ion) to carbon dioxide gas and the methanoate ion. Hydrogen peroxide oxidises the tartrate ion very slowly if there is no catalyst, even at elevated temperatures.
Cobalt(ll) ions are pink. The hydrogen peroxide initially oxidises the cobalt(II), Co2+, to cobalt(lll), Co3+, which is green. The cobalt(III) bonds to the tartrate ion, allowing the oxidation to take place. The CO3+ is then reduced back to CO2+ and the pink colour returns.
The cobalt catalyst provides an alternative route for the reaction to occur. This alternative route has a lower activation energy and the reaction proceeds much more quickly.
Health & Safety checked, February 2008
Web links
This website gives information about the ‘Traffic light’ experiment which can be done as a demonstration
www.rsc.org/Education/EiC/issues/2005July/Exhibitionchemistry.asp
(Website accessed August 2007)
Updated 29 Oct 2008Average rating: 
5 out of 5
Your reviews
To underline the fact that catalysts are regenerated at the end of the experiment, I repeat this using copper(II) sulphate, instead of the cobalt salt, which also speeds up the CO2 production considerably. However, the Cu2+ is reduced to the 1+ with the characteristic coloration, showing that this is a different reaction.
Submitted by: Graham Gisby on 10 November 2008
V.good - I like it!
Submitted by: abu abdulrahman on 27 January 2009
I used this experiment many times in the UK to demonstrate the notion that although the catalyst is in its original state in the reaction, the catalyst often changes during the reaction. The colour change during the reaction illustrates this perfectly.
Submitted by: Christine Ellis on 13 July 2009
I have used this experiment successfully for many years. I am now having a problem getting it to work! It goes from pink to green with effervescence, but then goes muddy green and will not go back to pink. I have changed the hydrogen peroxide and tartrate solutions (using new containers of each), but it still won't work. I have made fresh cobalt chloride solution too. Any ideas?
Submitted by: Steven England on 25 September 2009
Another must try!
Submitted by: CAROLE DONNAN on 4 October 2009
I LIKE SCIENCE!
Submitted by: TOM BRECKLES on 1 December 2009
The experiment is great. A little more chemistry for those bright and inquisitive students would be helpful.
Submitted by: Mike Carrington on 17 April 2008