This reaction involves the oxidation of potassium sodium tartrate by hydrogen peroxide using a colbalt salt as a catalyst.


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 demonstration.

Lesson organisation

The demonstration lasts about 15 minutes, longer if explaining the chemistry to an A-level audience.

It takes about 30 minutes to set up.

Apparatus Chemicals

Eye protection

Each demonstration requires:

Beaker (250 cm3)

Measuring cylinder (50 cm3)

Measuring cylinder (10 cm3)



Bunsen burner

Thermometer, -10 – 110 oC

Access to balance (1 d.p.)

Potassium sodium tartrate (Rochelle salt), 5 g

Hydrogen peroxide, 20 ‘volume’ (IRRITANT), 20 cm3

Cobalt(ll) chloride solution, 4% (TOXIC, DANGEROUS FOR THE ENVIRONMENT), 5 cm3

Distilled or deionised water, 60 cm3

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection.

Potassium sodium tartrate (Rochelle salt), KNaC4H4O6.4H2O(s) - see CLEAPSS Hazcard.

Hydrogen peroxide solution, H2O2(aq), (IRRITANT) - see CLEAPSS Hazcard and CLEAPSS Recipe Book. The 20 ‘vol’ solution is best made by diluting fresh 100 ‘vol’ hydrogen peroxide solution (HARMFUL, wear goggles and consider wearing gloves) for this demonstration.

Cobalt(ll) chloride solution, CoCl2(aq), (TOXIC) - see CLEAPSS Hazcard and CLEAPSS Recipe Book. Dissolve 0.2 g of cobalt(II) chloride-6-water (TOXIC, DANGEROUS FOR THE ENVIRONMENT) in 5 cm3 of distilled or deionised water.   


a Weigh 5 g of the potassium sodium tartrate into a 250 cm3 beaker. Add 60 cm3 of distilled water and stir to dissolve the solid. 

b Add 20 cm3 of 20 volume hydrogen peroxide solution to the solution in the beaker. Note any signs of reaction.

c Put the beaker on the tripod and gauze and heat the mixture in the beaker to about 70 °C. 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 2016


This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

Page last updated October 2015