Investigation to see how the concentration affects the rate of reaction.

There are three ways you can measure the speed of reaction:

1. Change in mass – Any reactions that produces gas can be carried out on a mass balance and as the gas is released the mass disappearing is easily measured.
2. Precipitation – This is when the product of the reaction is a precipitate which clouds the solution. Observe a marker through the solution and measure how long it takes for it to disappear.
3. The volume of gas given off – This involves the use of a gas syringe to measure how much gas is given off.

I plan to carry out an investigation to see how the concentration affects the rate of reaction. I will do this by mixing together water and invertase in a test tube. I will then add the concentration of sucrose solution. I will then measure the time it takes to go cloudy, know as the precipitation method.

Prediction:  I predict that during my experiment the higher the concentration the faster the reaction will occur and therefore the solution will go cloudy faster. This is because increasing the concentration of the reactants will increase the frequency of collisions between the two reactants.  This is because the molecules in the reaction mixture have a range of energy levels. When collisions occur, they do not always result in a reaction. If the two colliding molecules have sufficient energy they will react. If the concentration of any reactant in a solution is increased, the rate of reaction is increased. Increasing the concentration, increases the probability of a collision between reactant particles because there are more of them in the same volume and so increases the chance of a successful collision forming products. Below is a picture showing this:

Increasing the concentration of reactant A or B will increase the chance or frequency of collision between them and increase the speed of product formation (slower => faster).

I predict the graph will look something like this:

Equipment:

1. 5 test tubes – used to hold all the chemicals ready for the reaction to take place
2. A minimum of 45ml of invertase solution – used to break down the sucrose into sugars
3. A minimum of 45ml distilled water – Used to slow down the reaction
4. A minimum of 45ml sucrose solution – Used to react with the invertase solution
5. Thermometer – used to make sure that the water bath remains above to 70 degrees Celsius
6. Stop watch – used to calculate how long it takes for each solution to go cloudy
7. Water bath – used to denature the invertase
8. Benedict solution – Changes from blue to yellow or red in the presence of reducing sugars, such as glucose.

Method:

1. Mix water and invertase in a test tube, add the sucrose solution.
2. Start the timer and leave for two minuets for the invertase solution to break down the sucrose into sugars.
3. Prepare the water bath making sure that it stays above 70 degrees Celsius; this is so that the invertase is denatured.
4. After two minuets put the test tube in the water bath for another two minuets, to denature the enzyme.
5. Once the two minuets has finished take the test tube out of the water bath and add benedict’s solution.
6. Measure the time taken for the solution to turn from blue to cloudy yellow.
7. Record results, and then repeat the experiment again.

Safety:  I will make sure I handle all equipment with care, so to prevent any breakages. I will also wear a lap-coat and safety goggles. Finally I will handle all hot water with care and only mix the correct amounts of each solution.

Fair test: To make sure my results are as accurate as possible I will firstly keep all variables the same except the concentration of invertase for example I will maintain a constant temperature in the water bath  so not to affect the number of collisions between each molecule, I will also keep the same volume of solution in each test tube, I will wash pipettes through thoroughly before filling each test tube, I will wear gloves to prevent contamination, and finally I will use distilled water to prevent any impurities.

During my experiment I will need to keep both water and sucrose constant. I will change the concentration of invertase throughout a series of 5 or 6 tubes so that the change in results can clearly be seen. For my experiment I will use a maximum concentration of invertase of 1% and a minimum of 0%. I will take 6 readings in even steps, increasing by 0.2% each time to make sure each part of the range is investigated. Therefore my readings will be taken at o%, 0.2%, 0.4%, 0.6%, 0.8%, and 1%.

I will use the following calculation to work out the concentration of the invertase solution:

         Volume of invertase used

                                                                                              X 1%     =    concentration of invertase solution

   Volume of invertase used +

  Volume of distilled water used  

Below is a table showing my preliminary calculation based on 5(cm3) of solution:

Method of preliminary experiment: (Note: do each test tube one at a time)

1. Boil the kettle or check that the water bath is on using the thermometer, maintain at a temperature above 70 degrees Celsius.
2. Calculate the correct amount of invertase solution and distilled water for each of the 6 test tubes. Label each test tube and add the right amount of solution into each test tube.
3. Add 5ml of sucrose to each test tube and time for 2 minuets using the stop watch.  
4. After 2 minuets place the test tube  into the hot water bath/ water from the boiled kettle, and time for two minuets, this denatures the enzymes and stops the reaction from proceeding further. (Denature is the alteration of a protein shape through some form of external stress for example, by applying heat, acid or , in such a way that it will no longer is able to carry out its cellular function).
5. Once the 2 minutes are over take the test tube out of the hot water bath and add the benedict solution, at the same time start the stop-watch.
6. When the blue mixture changes to a cloudy yellow, stop the clock and record the time.
7. Carry out the experiment for each test tube and record results.

Preliminary results:

On the next page is a graph for my preliminary results:

After analysing my graph I can see that it does not produce a true curve, either my prediction is incorrect of my results are unreliable. To make sure that my actual results are more accurate I will increase the volume of solution. This is because after carrying out my preliminary test I learnt that the quantities of each solution where too small to measure out accurately and therefore this affected my results. I therefore hope to use this knowledge to improve my actual experiment.

Improved calculation table:

Improvements: I will now use increased volumes of each solution so that my measurements are more accurate. I will also repeat the experiment another 3 times and find the overall average to ensure the accuracy of my results.

I will need to work out the rate of reaction for each concentration of invertase in order to analysis my results. I will then plot these results onto a graph. The rate of reaction can be found using the following formula:

                                                                                                                                   

Average rate of reaction     =                                   1                                      

                                                   Average time taken for cloud to appear

Table of results:

As my results are very similar in each reading this confirms that my results are accurate and therefore reliable.

On the two pages are graphs showing the average /secs it took each concentration of invertase (%) to turn cloudy yellow. These results then allowed me to go on and create a second graph showing how the rate of reaction is affected by the concentration of invertase (%).

                             

Conclusion: After analysing graph two I can conclude the following:

After plotting the coordinates and drawing a line of best fit I can see that the results have a positive correlation which ascends in a straight line. This can be proven as for every 0.2% increase of invertase the average rate of reaction increases by an average of 0.02 seconds. This therefore supports my previous prediction that as the concentration of invertase increases so does the rate of reaction.  This is because invertase is a biological catalyst which increases the rate of reaction. From my results I can now work out an equation which could be used to predict the average rate of reaction for any concentration of invertase. This equation is x = 10y e.g. if I wanted to calculate the average rate of reaction for invertase concentration of 0.4 it would be 0.04.  From these results I can now see that all previous predictions where correct. I have now proved that the concentration of invertase does affect the rate of reaction.

Evaluation:

Although my experiment did work efficiently and give me results accurate enough to prove my initial aim and analysis a pattern clearly, improvements could still have been made to make my results more precise. Firstly there where some anomalous results during my experiment; for example at a concentration of 0.08%  invertase  the rate of reaction calculated was 0.09, however from my prediction and my graph I can see that this reaction rate should have been 0.08. This result could have been affected by the following:

• Temperature in water bath may have varied depending on where the tube was in the water bath.
• Inaccurate volumes of the solutions, due to mistaken measurement of the solutions.
• The level of cloudiness may have been interpreted differently by different people.
• The temperature may not have remained constant throughout each experiment.
• The concentration of invertase may have still been too small a percentage and therefore incorrectly measured.
• It may have been difficult to read the level of solution on the test tube due to refraction.

To improve my results I would change the following:

1. Firstly I could use a colorimeter which gives a far more accurate reading for cloudiness compared to judging by eye. However if this equipment was unavailable I would also make sure that the same person judged it each time therefore to prevent inaccurate results as peoples opinions may vary on when the solution has turned cloudy.
2. I would also leave the thermometer in the water throughout my experiment enabling me to check the water bath temperature is remaining constant.
3. To also have more accurate measurements of each solution I would use greater volumes making it easier to measure.
4. Furthermore I could use a burette to measure out the volumes of solution which may help to improve accuracy.

Overall my results where fairly reliable; they allowed me to see the relationship between the concentration of invertase and the rate of reaction, which lead me to conclude that my prediction was correct. I could now go on to study other factors which could affect the rate of reaction, for example temperature, size of particles, a catalyst being present, ect.