name the following :-
1) this is the process of separating a pure substance in the form of crystals from its hot saturated solution by cooling
2) by adding this acid , rate of decomposition of H2O2 reduces
3) these types of substances improve the efficiency of a catalyrt
4) in this type of reaction , a more reactive element displaces a less reactive element from its compound
5) in this type of change overall change in energy takes places energy is either absorbed or released
Answers
Answer:
Using an enzyme catalyst
In many living organisms hydrogen peroxide is a product of metabolism that must be broken down, since in appreciable concentrations it is toxic. The rate of decomposition is increased by the intra-cellular enzyme catalase.
As a fairly simple project you could compare the effectiveness of the enzyme from different sources such as potato, celery and liver. This might lead you on to a more thorough investigation of other factors that affect the activity of the catalase, including, perhaps, temperature, pH, concentrations of substrate and enzyme and the presence of enzyme inhibitors.
Such experiments may at first sight seem quite straightforward, but as you try to interpret your results you will be led into quite complex, but very interesting, aspects of chemical kinetics and reaction mechanisms.
Using an inorganic catalyst
As an interesting contrast, a similar increase in the rate of decomposition of hydrogen peroxide can be achieved using an inorganic catalyst such as manganese(IV) oxide or lead(lV) oxide.
You could set out to look at how factors such as concentration of the peroxide, amount of the catalyst and temperature affect the rate of the decomposition. Experiments of this kind could lead you towards a possible reaction mechanism and towards the calculation of the activation energy involved.
Contact lens chemistry
The catalytic decomposition of hydrogen peroxide will be very familiar to some students, as it is an integral part of one system for cleaning contact lenses. In this method the l8 December, 2008 clean it and then the remaining solution is decomposed with the help of a platinum-coated catalyst. You might like to investigate how the effectiveness of this catalyst changes under different conditions and compare it with the other catalysts.
Monitoring the decomposition
There are several ways in which you can monitor the decomposition reaction. You might decide to follow the fall in concentration of the hydrogen peroxide. You can do this by taking samples of the reaction mixture at different times and running them into an acidified solution of potassium iodide. The iodine produced can be titrated with a solution of thiosulphate using starch indicator:
2H+ + H2O2 + 2I– → I2 + 2H2O
I2 + 2S2O32– → 2I– + S4O6 2–
The volume of thiosulphate solution required for the titration provides a measure of the amount of hydrogen peroxide in the reaction mixture at the different times. As an alternative you might prefer to measure the volume of oxygen produced during the decomposition of the hydrogen peroxide. You can do this by connecting a glass gas syringe to a Buchner flask or Hirsch tube.
There is also another, more novel, approach to monitoring the enzyme-catalysed reaction which you might like to try. First, prepare a catalase extract. Next, use a file paper hole punch to stamp out circles from a filter paper. Soak one of these circles in the enzyme extract, drain, then use a glass rod to poke it to the bottom of a test tube containing the hydrogen peroxide solution. The bubbles of oxygen generated by the decomposition of the peroxide stick to the filter paper circle and carry it to the liquid surface. The time taken for this to happen provides a surprisingly accurate measure of the relative activity of the enzyme under different conditions.