C6 H 12 O 6 + 6O2 → 6CO2 + 6H2O + 29OO kilojoules(kJ)
glucose + oxygen → carbon + water + Energy
dioxide
When this process occurs in our cells, about twenty separate chemicals reactions are needed to convert the reactants (glucose and oxygen) into the products (carbon dioxide and water). The large amount of energy produced help to keep us warm (heat) and mechanical energy in our muscles to help us move around and to keep our heart and breathing muscles working. About half of the energy from cellular respiration is released as heat. This explains why you get hot whilst running. Your body uses up more food therefor more heat is produced.
Yeast
Yeast contains tiny single-celled organisms which can respire aerobically like animals and plants. Yeast is normally related to a certain group of microscopic fungi and to commercial products consisting of masses of dried yeast cells. Although a number of fungi are sometimes called yeast’s, the true yeast’s are unicellular, consist of oval or round cells and reproduce quickly by budding. When yeast reacts it doubles itself on and on again.
Yeast has long been of commercial importance because it is the main agent in brewing, wine making and the fermentation process. Yeast is also used in bread making as it acts upon the carbohydrates in the dough, forming carbon dioxide and ethyl alcohol which are lost in the baking process. The escaping carbon dioxide causes the bread to rise.
Prediction
I predict by raising the temperature in which the reaction takes place, the rate of reaction between hydrogen peroxide and the yeast solution will double. I expect to see the solution turn from in active to very reactive when mixed but it will cease to react above 40°C and then decrease in reactivity. We know from the kinetic theory of matter every thing is made up of moving particles. There are particles in all materials – glass, wood, paper, water, petrol, air etc. These individual particles are very very small and cannot be seen by the naked eye. The particles of different substances have different sizes. The particles in all substances are continually moving. As the temperature rises the particles get hotter. They have more energy and move around faster. Most catalysed reactions go faster as the temperature rises but above 40°C their reaction rate decreases rapidly because the enzymes are proteins and there structure is damaged as the temperature rises above 40°C. This damage to the protein structure is called denaturation. As the protein is denatured, it becomes less and less effective as a catalyst and the enzyme-catalysed reaction get slower and eventually stops.
Independent variables
My independent variable within this practical experiment is temperature my aim is to raise the temperature of the water baths by 10°C each time and record in cm3 the amount of gas given off per 10 seconds. I will repeat the experiment three times at temperatures of 10°c, 20°c, 30°c, 40°c and 50°c and record the results. The range of the temperatures being taken is 40°c.
Dependant Variables
My dependant variable will be to measure the temperature with a thermometer in to verify the temperature is correct giving me accurate results. I will also be measuring the volume of O2 given off in cm3 per 10 seconds. I will measure this in cm3 using a syringe body to collect the gas.
Control Variables
The quantity of yeast and hydrogen peroxide solutions will be equally diluted for each test. I will carry out each test three times at each temperature and record the results.
Pilot study
I found that you have to get organised quickly and efficiently so as to get results during the lesson.
Method
To carry out the practical the following should be done:
- Apply safety goggles and wear lab coat.
- Obtain 1 500ml beaker and ¾ fill it with water.
- Obtain 1 rubber bung with a hypodermic needle in it.
- Obtain a piece of plasticine and place it on the syringe body.
- Obtain 1 water bath and turn it on at the desired temperature.
- Obtain 2ml of 10% diluted hydrogen peroxide solution.
- Obtain 2ml of 10% diluted Yeast solution.
- Then insert the Hydrogen peroxide solution in to the test tube.
- Obtain a stopwatch so you can time the test.
- Obtain pen & paper to record your results.
- Insert the yeast solution.
- Record results every 10 seconds.
- When the reaction finishes repeat twice more (3 results in total).
- Move to the next water bath and repeat the above with a new test tube.
- Tidy up and dispose of solutions safely.
Apparatus
The following apparatus was used in the experiment:
Water bath (to change the temperature of the experiment)
Test tubes (to withhold the solutions when reacting)
Delivery tube (to direct gas being given off to the syringe body)
Rubber bung (to prevent gas leakage)
500ml beaker (to hold water)
Hypodermic needle (to allow direct insertion in to the test tube)
Syringe (to insert solutions in to the test tube)
Syringe body (to collect gas bubbling out of the delivery tube)
Plasticine (to prevent leakage of gas from syringe body)
2ml of H2O2 solution (10% H2O2 diluted in water)
2ml of Yeast solution (10% Yeast diluted in water)
Stopwatch (to monitor the time of the reaction)
Pen & Paper (to record results of experiment)
Lab coat (to protect clothing from solutions)
Safety glasses (to protect eyes from ‘blowback’)
Safety audit
In the practical safety is vital so I took these safety precautions:
I made sure that the yeast solution was the one in the syringe at all times in case of blowback in which it would fly over my head rather than hydrogen peroxide. I made sure that I was wearing safety goggles at all times and a lab coat as hydrogen peroxide could damage my eyes or corrode my skin.
Conclusion
In conclusion and by way of summary I found my hypothesis held true as it proved to be correct my hypothesis was: I predict by raising the temperature in which the reaction takes place, the rate of reaction between hydrogen peroxide and the yeast solution will double. I expect to see the solution turn from in active to very reactive when mixed but it will cease to react above 40°c and then decrease in reactivity.
The rate of reaction did increase between 30°c and 40°c but above forty the rate of reaction decreased. This proved my hypothesis to be correct but not entirely as it didn’t double in the rate of reaction.
Evaluation
In my experiment some of my results didn’t quite fit this may have been the cause of poor preparation or the way I carried out the experiment. Some of the problems I found in my experiment were:
- I should have let the reaction fully finish so that I could obtain a wider range of results giving me more to work on and adjust. I should have started recording at 5 seconds until 110 seconds.
- I should have let the solution warm up while it was sitting in the water bath rather than start straight away.
- The recording of data may not have been accurate due to the repeated rising in temperature whilst you are trying to take a reading. This may have been the reason why the results didn’t double up.
- In a classroom environment people are pushing and shoving and so the solutions may have been mixed causing a difference in results.
- I rushed obtaining my results and this may have caused me to predict what should be there rather than what is there.
- There was not enough lab equipment as people were taking other peoples apparatus which led to confusion and panic.
