Since we are considering the effect of temperature on the reaction, all other variables (including number of yeast balls used and volume and concentration of the glucose solution) must be kept constant throughout.
Amount of precipitate formed
Reaction Rate = time
Extent of reaction
= time
When the glucose solution reacts with the yeast, carbon dioxide is formed. The amount of gas formed in a certain time can be used as an indicator of reaction rate.
In order for a reaction to occur, reactant particles must collide with a certain minimum energy – activation energy
Increasing reaction rate results from : - more collisions
- more energetic collisions
When performing rates experiments, we must have a suitable way of measuring the extent of the reaction.
It is essential to alter only one factor at any given time. This is called fair testing.
Concentration affects reactions, so it must be ensured that the concentration of glucose solution and of the number of yeast balls remains constant throughout.
Increased temperature means an increase in kinetic energy of the molecule, hence a greater reactivity.
Hypotheses:
The higher the temperature of the reaction, the faster the reaction rate. I believe that this will be true until about 70 oC, at which point the yeast cells shall start to denature. This means that it will affect the upper values.
Key: - HCl molecule - yeast cell
There is the same amount of acid and yeast in both container (i) and (ii), but container (ii) has a higher reacting temperature. Therefore, it speeds up the random motion of molecules and the yeast cells will have much more energy and therefore, collide quicker and with more force. This means that the reaction will occur much quicker.
As the temperature increases, the time taken for 1cm3 of CO2 to be produced decreases, meaning the reaction rate is faster. And as the values for the reaction rate are directly proportional to 1/t (or indirectly proportional to t), I have drawn up the above hypotheses graphs.
Safety:
Some safety precautions were undertaken to ensure no serious accidents occurred:
- No running in the lab
- No bags allowed near practical area of the lab
- Lab coats were worn to ensure that if any spillages occurred, they did not affect your clothes
- Safety goggles were also worn, in case any solutions splashed up towards the eyes.
- Washing hands after the experiment to ensure that no residue was left on fingers which could infect
Diagram:
Preliminary Experiment:
A preliminary experiment was performed to see whether the reaction works, and what needed to be improved on before the main experiment.
To discover reaction rate, we need to decide how to measure the volume of gas produced. The two main options are:
-
Check every x minutes and record how much gas has been produced.
-
See how long it takes to make x cm3 of carbon dioxide.
Both were performed, but the first option takes a very long time at low temperatures, and for a realistic comparison to be made, that same time scale would have to be used for every temperature. So, I have therefore decided to see how long it takes to make x cm3 carbon dioxide.
Now I have to decide how much CO2 am I looking to collect for the experiment. Having said that at low temperatures, the reaction rate is very slow, I have decided to see how long it takes for 1cm3 to be collected.
Also, to ensure that the experiment was correct, I set up another one, where instead of collecting the CO2, I bubbled it through HCIS solution, to ensure that it was in fact carbon dioxide. This proved positive.
The results are as follows:
These results are not as I predicted, and so I can see that I have either made an error, or my hypothesis was wrong. However, after talking to the rest of the class, I have decided that the yeast must have been a bad batch, because nobody really got good results.