Is there a substitute for indigo carmine?

[vlclabbie]

To do a prac called 'traffic lights' but have none...

Thanks guys!

[kimmy]

this is a traffic light experiment that we have dont know if it is the same as what you are doing or not

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.


Apparatus and chemicals
Eye protection

Each group of students requires:
Beaker ml
Measuring cylinder (ml
Measuring cylinder ml
Tripod
Gauze
Bunsen burner
Thermometer, 10 oC – 110 oC
Access to balance (1 d.p.)

Potassium sodium tartrate (Rochelle salt)
Hydrogen peroxide (20 volume)
Cobalt(ll) chloride solution, 4%
Distilled water


a Weigh 4 g of the potassium sodium tartrate into a 250ml beaker. Add 50ml 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 mlof 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 ml 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.

[color=#80FF00]This is an impressive demonstration of how a catalyst is involved in the progress of a reaction. Students can add another 10 ml 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.[/color]

[vlclabbie]

Thanks Kimmy!