Conclusion
As we gathered very little information we can not make a accurate conclusion but, the one we do make is that our prediction is right “as the concentration of glucose increases in the solution, the time in which it takes the reaction in the solution to turn clear, will decrease.”
Evaluation
As you can see from the above table the reactions took so long that we did not wait to find out how long they took to react, to overcome this problem we diluted the potassium manganate (IIV) to a ratio of 1part potassium manganate (IIV) to 10parts water. As you can see this improvement of ours worked as it speeded up the reaction significantly. Another fault we found was the reactions did not only take a long time but they also turned a brownie colour. We did not overcome this problem until we did the experiment a second time.
Method
The intervals in which we will change the concentration of the glucose will be 5cm³, we did not chose10 as an interval as we would not gather enough information to be accurate, and an interval of 2.5cm³ would mean to many unnecessary reading. The concentration of potassium manganate (IIV) will always remain at 5cm³.
How many observations / measurements will be taken
We will repeat the whole experiment 3 times, in each experiment there will be 6 different concentration mixtures of potassium manganate (IIV) and glucose, see table of mixtures.
Number of measurements taken at each individual height
As the whole experiment will be repeated 3 times, we will be able to take an average for each concentration mixture and from these average results draw a graph.
Safety
We will overcome the problem of safety by remaining at ground level throughout the experiment; this will overcome the problem and danger of standing on a stool or chair. Before we began we would clear the area of obstructions such as bag’s, chairs and we will clear the desk of any books pencil cases etc.
First we collected the following apparatus;
- 6 beakers,
- 1 stop clock,
- 7, 10cm³ measuring cylinders,
- 2, 25cm³ measuring cylinders,
- 105cm³ of glucose,
- 30cm³ of potassium manganate (IIV),
- 75cm³ of water,
- some scrap paper,
- a book with results table,
We then assembled the apparatus as follows
- we chose a non congested corner of the laboratory were there was no obstructions, and were not near any doors so that there would be no draft,
- We wrote on the strips of scrap paper each different combination of solutions, these were placed in a line with a beaker on each,
- We then carefully measured out the liquids from the bottom of the meniscus accurate to 0.5cm³, and poured them into the appropriate beakers,
- After we had double checked all the measurements, we placed each liquid except the 5cm³ of glucose in the beakers we ticked off the specific liquid on the scrap labels, we did this incase we forgot if we had or had not added the liquid to the beaker,
- Once we had measured and added all the liquids in the correct beakers we then along with some help from another group poured in the 5cm³ of glucose which was in the 10cm³ measuring cylinder into the rest of the solution which was in the beakers, at this moment when the glucose was added the stop clock was started,
- We carefully observed each beaker but paid more attention to the beaker with the highest concentration of glucose, as this was the reaction we expected to react most quickly,
- As the solution began to turn clearer we observed the beaker closely and when it turned completely clear we took the time in the stop clock and wrote into our table of results. We repeated this process for each beaker using the first beaker’s solution as a comparison of clarity to the others to be more precise when it actually became clear. This method is called an end point.
Modifications
Since doing an initial test we have noticed that there are certain modifications that could be done to the experiment to improve accuracy and therefore our results. These improvements are
- We noticed that the solutions did not turn clear but went a brownish colour, this meant that these results were void,
- The answer to the above problem is to add 5cm³ (1M) sulphuric acid, when added the solutions reacted as they did before but the end results were that the solution did not go a brownish colour but turned clear.
Secondary information
Collision theory
Collision theory explains how chemical reactions occur and why rates of reaction differ. For a reaction to occur, particles must collide. If the collision causes a chemical change it is referred to as a fruitful collision.
Collision theory, the theory that explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called fruitful collisions. The fruitful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more fruitful collisions, increasing the rate of reaction.
When a undergoes collision with the reactant molecules, less energy is required for the chemical change to take place, and hence more collisions have sufficient energy for reaction to occur. The reaction rate therefore increases.
Reaction
In chemistry, the coming together of two or more atoms, ions, or molecules with the result that a chemical change takes place; that is, a change that occurs when two or more substances interact with each other, resulting in the production of different substances with different chemical compositions. The nature of the reaction is portrayed by a .
Chemical equations show the reactants and products of a chemical reaction by using chemical symbols and formulae. State symbols and the energy symbol (H) can be used to show whether reactants and products are solids, liquids, or gases, and whether energy has been released or absorbed during the reaction. In addition reactions two or more compounds react together to form one compound.
Energy of reaction
Energy released or absorbed during a chemical reaction is also called heat of reaction. In a chemical reaction, the energy stored in the reacting molecules is rarely the same as that stored in the product molecules. Depending on which is the greater, energy is either released (an exothermic reaction) or absorbed (an endothermic reaction) from the surroundings (see ). The amount of energy released or absorbed by the quantities of substances represented by the chemical equation is the energy of reaction.
Conservation of energy
In chemistry, the principle that states that in a chemical reaction, the total amount of energy in the system remains unchanged. For each component there may be changes in energy due to change of physical state, changes in the nature of chemical bonds, and either an input or output of energy. However, there is no net gain or loss of energy.
Activation energy
In chemistry, the energy required in order to start a chemical reaction. Some elements and compounds will react together merely by bringing them into contact (spontaneous reaction). For others it is necessary to supply energy in order to start the reaction, even if there is ultimately a net output of energy. This initial energy is the activation energy.
Activation energy diagram
Progress of a reaction and the process of the reactants turning into products can be plotted as you can see below.
Going From the bold line labelled reactants to the top of the curve, you are now going up the energy scale. Energy is being put into to break these bonds, in this case in the form of heat. Bonds in the reactants have been broken at the top of the curve. The amount of energy that it took to break the bonds is called the reaction energy. Activation energy is the minimum amount of energy necessary to be inputted to the reaction for the reaction to occur. (a catalyst may work by lowering the activation energy of a reaction therefore increasing the speed of the reaction.
Going from the top of the curve to the products, you are going down the energy scale, energy (heat) is given off as bonds form in the products.
The reactants are higher up the energy scale than the products, this is because the amount of energy (heat) you need to put in (the activation energy) is less than the amount of energy (heat) you get out. This is a typical exothermic reaction.
The difference in energy levels between the reactants and the products is given the symbol DH (pronounced “delta H”0. This is the amount of heat given out )or taken in) during the reaction. For an exothermic reaction, DH is negative.
For an endothermic reaction, DH is positive.
Rate of reaction
The rate of reaction is the speed at which a chemical reaction proceeds. It is usually expressed in terms of the concentration (usually in per litre) of a reactant consumed, or product formed, in unit time; so the units would be moles per litre per second (mol l–1 s–1). The concentration of the reactants and the temperature of the reactants (or the presence of a ) may effect the rate of reaction. During a reaction at constant temperature the concentration of the reactants decreases and so the rate of reaction decreases. These changes can be represented by drawing graphs.
The rate of reaction is at its greatest at the beginning of the reaction and it gradually slows down. For an (one that absorbs heat) increasing the temperature may produce large increases in the rate of reaction. A 10°C rise can double the rate while a 40°C rise can produce a 50–100-fold increase in the rate.
is used to explain these effects. Increasing the concentration or the pressure of a gas means there are more particles per unit volume, therefore there are more collisions and more fruitful collisions. Increasing the temperature makes the particles move much faster, resulting in more collisions per unit time and more fruitful collisions; consequently the rate increases.
Obtaining
1st Experiment
Results
Below is a table that shows the results that we obtained.
Graph showing reaction between potassium manganate (IIV) and glucose
On separate sheet over leaf.
Obtaining
I will use in my experiment the following apparatus;
- 6 beakers,
- 1 stop clock,
- 7, 10cm³ measuring cylinders,
- 2, 25cm³ measuring cylinders,
- 105cm³ of glucose,
- 30cm³ of potassium manganate (IIV),
- 75cm³ of water,
- some scrap paper,
- a book with results table,
For instructions of how I assembled this apparatus please see method.
Analysing
Below there is a diagram of how we set up the apparatus for the experiment.
From analysing my results I can see a pattern that, as the concentration of glucose increases so the time in which it takes the potassium manganate (IIV) to react with the glucose to turn colourless decreases. I predicted this to happen, because if there is more glucose in the solution, this means that there is a higher chance that it will collide with the potassium manganate (IIV), increasing the chance of a reaction, therefore speeding up the reaction. This related back to the collision theory, the more molecules the more likely the chance of collision and therefore more chance of a fruitful reaction. I am happy to say that from analysing my results that my prediction was correct, from using scientific knowledge I can now explain why, see scientific knowledge.
Conclusion
My overall conclusion from doing the preliminary and final experiments is that my prediction at the beginning was correct - “I predict that as the concentration of glucose increases in the solution, the time in which it takes the reaction in the solution to turn clear, will decrease”. This statement can now be reinforced with information that I have gained from doing these experiments (see table of results and graph). As the concentration of glucose increases so the time in which it takes the potassium manganate (IIV) to react with the glucose to turn colourless decreases.
Evaluation
From designing and carrying out these experiments I have noticed areas which can be improved. These improvements will make the experiment more accurate and will therefore make my final conclusion more accurate. These improvements are as follows :-
- Make measurements of all liquids as accurate as possible, this may involve less human input to the measurements as human error is one of the largest factors in the less accuracy of measurements,
- Use a more accurate method of determining whether or not the reaction has finished, instead of human judgement,
- Use a more accurate method of timing the reaction, e.g. stop watch, this is because the stop clock we used was only accurate to 1 second,
-
Use a fairer method of combining the to liquids, we noticed as we poured the potassium manganate (IIV) our into the beaker, that we did not pour them in from the same height, this means that some solutions had more potential energy which could then be converted into kinetic energy, this could result in one solution colliding quicker, and therefore reacting quicker,
- Use a more accurate method of measuring the temperature of the liquids and the room. This is because whilst repeating the experiment, we noticed that when we examined the results of the experiment on the colder day, the experiment took longer than it did on the hotter day. This is because on the hotter day the solutions had more energy already in them, this was in them in the form of heat, this then means that the time taken for them to reach their activation energy was less resulting in a quicker reaction.
If I was to repeat this experiment I would not only try and make it more accurate by using more accurate equipment, but I would also take more repeat readings and take readings at smaller intervals. By doing this, the results would give me more accurate information to analyse and conclude.
