Investigating the effect of temperature on the rate of chemical reaction when an Alka-Seltzer tablet is dissolved in water and to estimate the temperature change needed to double the rate of reaction.

                            higher the temperature, the greater the energy the particles

                            have and therefore the faster and further they move. There

                            are more collisions, which happen more often, which

                              means the rate of reaction would be higher. The lower the

                              temperature, the less collisions as there is less energy

                              which means the reaction would be slower. In order to

                              control temperature I will use a water bath so the temper-

                              ature remains constant, using a thermometer to measure

                              the temperature is being kept the same.

                                 

                               

∙ Gas collected – I have to make sure that in my experiment I always collect

                            the same amount of gas in the gas syringe, so I may com-

                            pare the results in the end. I will time how long it will take

                            to collect 100 cm of gas.

∙ Surface area – The larger the surface area of the tablet, the faster the rate

                           of reaction will be. This is due to the fact that the more

                           tablet particles are in contact with the water particles at one

                           time. This means more collisions occur, more often which

                           means the time period the experiment takes is shorter, than

                           if there was a smaller surface area. A tablet which has a

                           larger surface area would dissolve faster in water. In my

                           experiment the surface area of the tablet can be enlarged by

                           crushing it up. In order to control the surface area in my

                           experiment I will use the same tablets from the same box.

♦ Scientific Explanation

In a chemical reaction, the starting materials are called reactants, and the finishing materials are called products. If the reactants take a short time to turn into products, it is a fast reaction. The speed or rate of reaction is said to be high. There are many factors, which may affect the rate of reaction:

∙ The size of the particles of a solid reactant

∙ The concentration of reactants in solution

∙ The temperature

∙ The presence of light

∙ The addition of a catalyst

However in this investigation I am going to concentrate on the effect of the temperature on the rate of reaction. The rate of reaction depends on how often and with how much energy the reacting particles collide with each other. As the diagrams below show:

For the reaction to take place the particles have to collide with certain energy. Therefore, for a chemical reaction to occur, effective collisions must be occurring. These collisions have a sufficient energy. Every chemical reaction has a certain Activation Energy and to increase the rate of reaction you must increase the possibility of the reactant particles having that energy. One of the ways of doing it, is to increase the temperature. The higher the temperature, the greater the kinetic energy of the particles, therefore there will be more collisions with enough energy to make reaction happen. This is explained in the Maxwell-Boltzman distribution below:

When the temperature is low, the particles do not have enough energy to pass the Activation Energy line. Only a few of them do. This means that only a few molecules have the required energy to react with other molecules. Therefore, the rate of reaction is slow. However, when the temperature is high, more molecules pass the Activation Energy line and react with the other molecules. This means the rate of reaction increases, as there are more collisions. The Maxwell-Boltzman distribution curve shows us the Activation Energy and how many molecules have the required energy to react. For T1, which is a lower temperature, it is clear that most of the molecules do not have the required energy to pass the Activation Energy line. The area under the curve is the number of molecules. We can see that T2 has a larger area past the Activation Energy line, which means that more molecules have the energy to react, as this reaction is faster.

♦ Plan

Apparatus:

• 15 Alka-Seltzer tablets
• A lab coat
• A pair of safety goggles
• A Bunsen burner
• A tripod
• A gauze
• A conical flask
• A large beaker
• A 50 cm  measuring cylinder
• A thermometer
• A 100 cm  gas syringe and bung
• A stop watch
• Top-pan scale

These pieces of apparatus will need to be set up in a particular way to be as useful as possible. Here is a diagram to show how this apparatus should be placed:

Method:

The experiment must be carried out accurately and fairly, so that the results can be trusted as reliable. Here is a method of how I shall be carrying out the investigation, using all the apparatus mentioned above.

1. Set up the apparatus above.
2. Light the Bunsen Burner and heat a large beaker of water.
3. Measure out 50 cm  of water using the measuring cylinder and then pour into conical flask.
4. Place the conical flask in the water bath, and slowly heat the water, checking the temperature with the thermometer.
5. When the water in the conical flask has reached the temperature of 20°C, remove the conical flask from the water bath.
6. Open the package containing an Alka-Seltzer tablet and ensure the stopwatch is set to display 00.00.00 minutes.
7. All at the same time, drop the tablet in the conical flask placing the bung, attached to the gas syringe, into the top of the conical flask.
8. Only start the stop watch when the tablet entered into the conical flask.
9. Keep an eye on the syringe and stop the stopwatch once it has reached 100 cm  .
10.  Record the amount of time taken for the syringe to reach 100 cm .
11.  Discard the contents of the conical flask and rinse it.
12.  Rinse the thermometer and dry them off.
13.  Repeat this experiment another two times.(Altogether you should  

 have 3 reading)

14. Then change the temperature you heat the water. (Preliminary work will determine the temperatures.)
15.  For each temperature, repeat the experiment three times.

♦ Prediction

I predict that as I increase the temperature of water, the rate of the chemical reaction will also increase. I predict that the rate of reaction will double each time I increase the temperature by 10°C. This is because as the temperature increases, the water particles will have more energy so will move about with more energy and speed. This will result in more collisions with the particles of the Alka-Seltzer tablet. Therefore, this should lead to the tablet dissolving in the water at a faster rate.

        

Once the tablet has dissolved, the reaction can take place. The reaction is between the two distinct types of particles that the Alka-Seltzer tablets are made of. These are Sodium Bicarbonate particles and Citric Acid particles. When these collide with enough energy to break their bonds, they cause a reaction, which results in the production of carbon dioxide. It is this gas, which is collected in the gas syringe, and used to work out the rate of reaction. The temperature affects this reaction, by providing the particles with more or less energy. A larger amount of energy does two things, both which help to increase the rate of reaction. Firstly it means the particles can more about faster, so have more of a chance of multiple collisions. Secondly, it means the particles collide with enough force to break the bonds and cause the reaction.

The equation for this reaction is;

Sodium Bicarbonate + Citric Acid ~> Carbon Dioxide + Sodium Citrate + Water  

        Other than temperature, the concentration of the solution also affects the speed of the reaction. The smaller the volume the faster the reaction as the particles is spaced out over a smaller area. This means that collisions will be more frequent than if the solution was much more concentrated.