From these results it is clear that the best amounts ton use is 50 cm² of hydrochloric acid and 1 cm of magnesium ribbon. This is what we decided to use among out group. This is a systematic mistake and it will not effect the results in a very bad way.
Ways of following a reaction
Their are four general ways of following a reaction in Chemistry. I will have to deside which one we will follow, this is the base foe our method.
I used the Chemistry revision guides that we have in school to find out about these different methods. The first method is precipitation. This is used in precipitation reactions when the reaction has one of the products solid. Usually a cross would be drawn on a peace of paper and placed under a beaker in which the reaction is going to take place. The solid formed will gradually make the cross invincible. The time it takes to do that is measured and recorded.
The second type of measurement involves weighing the beaker in which the reaction is going to take place. The change in mass will be recorded as gas is given of. The time when the reaction has ended could be see when the mass of the reactants will stop to change. Sometimes the mass will be recorded constantly, every 10 seconds or something like this, then graph to show the speed of reaction at different stages of the reaction could be drawn. Very accurate weighing scales will be needed because often the mass of the gas given of is very small.
An other quite accurate way of measuring would be to measure the volume of gas that is given of. The reactions at different conditions will give out the same amount of gas but at different rates, this is what will course the reaction to be faster. A gas cylinder and a conic flask will be needed to do this kind of experiment. Here to the rate of reaction (=gas given off) will usually be measure throughout the experiment.
The last method is the easiest to do. This is simply timing the time it takes for the reaction to end. It is considered to end when one will not be able to see anything going on. A stopwatch will be started when the reactants are placed together and stooped that they have fully reacted. If a gas produced then it will be easy to see when the reaction ends.
It was not very hard to choose the method to do our practical with. The first, precipitation method was not suitable, the reaction that we are looking at is not a precipitation reaction it is an exothermic one, a precipitation reaction is usually between two liquids. Water bath will be needed for safety and to keep the acid at needed temperature, so the second and third method would be too complicated. Also I do not think that our school can provide us with the weighing scales accurate enough to be able to record the mass change, because it is going to be very small. We tried to make the reaction change the temperature as less as possible so their is going to be only a little volume of gas given off, this may lead to the third method not being accurate, also the gas cylinders are very fragile, expensive and need gentle treating which we will not be able to give in the time provided. The gas may also expand with change of temperature and this will give misleading results. The best method that we could use was the timing. We were already familiar with it juring the preliminary work so this was the method that was chosen by our group.
Prediction
I think that the rate of reaction is going to increase as the temperature is going to be increased. There are some research I have done from the ‘GCSE Double Science, Chemistry. The Revision guide, Higher Level, Third Edition- for 2000 and beyond.’ On page 79 in the relative section this is what I found:
“When the temperature is increased the particles all move quicker. If they’re moving quicker, they’re going to have more collisions.”
The second relative quote was on the same page:
“The rate of a reaction simply depends on how often and how hard the reacting particles collide with each other.”
Together these statements show that temperature increases the rate of reaction. This is a source of material that I can trust.
I have also researched the effect of a ten degrees temperature increase on rate of reaction. It is proven that this doubles the rate of most reactions. This time the research was done in the internet, the firs useful website that I have found was:
“http://scidiv.bcc.ctc.edu/wv/7/0007-005-rea-t-cat.html”
Under the following title the above was clearly stated.
“Collision theory and temperature effects on rates
Reaction rates are roughly doubled when the temperature increases by 10 degrees Kelvin.”
Scientific knowledge
The increase in temperature is an increase in the energy that each individual molecule has on average. The increase in energy that molecules have is what makes the move round faster. The reaction can only take place after a collision, an effective collision. The effective collisions are though which take place between the two molecules of the reactants and if they collide at a sufficient speed. The increase in temperature increases the number of molecules that have the speed enough to make an effective collision, therefore the probability of effective collisions increases. Also the collision frequency increases and this to has an impact on probability to make it bigger. The energy that is spend to heat the substances can only be used to increase the speed at which the molecules go, so substances with higher temperature must have the molecules moving faster. The probability of effective collisions means that there are going to be more of them, so the rate of reaction will increase. There are so many molecules in the substances that are used and this means that probability is equal almost6 exactly to what will happen with the real reaction. More effective collisions mean that the rate of reaction will increase.
Some further research I have done is about ‘Maxwell and Boltzman’ theory. This is about the temperature and how it affects the rate of reaction. I have drawn a graph that helps to explain it. This is general and dose not have any numbers on because it could be interpreted for any reaction. The graph shows curves for different temperatures, one 20ºC and another one 30ºC. It also shows the different numbers of molecules that are any given temperature. The area that is belief the two curves is equal to the number of molecules, it is the same for both curves. But they are distributed differently. The highest point in the curve is where the most molecules are and the most molecules in 30ºC have a higher temperature. However we are especially interested in the molecules that are after the line of temperature enough to make an effective collision. It could be clearly seen that the numbers of molecules is higher for the 30ºC curve then for the 20ºC. The area equals to the number of molecules and it is shaded in pencil for the 20ºC curve, and the area under 30ºC curve is shaded with blue lines. It could be easily seen the the area shaded in blue covers all the pencil shaded area and extends beyond that. Also it is roughly twice as big because the temperature is a ten degrees rice. This theory is backed up by many experiments and is scientifically proven. I did not generalise the temperature because it is also important to see that their is a ten degrees difference. Rate of reaction depends on the number of molecules that have sufficient energy to make an effective collision' more particles- faster rate of reaction.
Apparatus
The apparatus bellow will be all needed for my method.
- Large beaker
- Small beaker
- 2 thermometers
- Timer
- Buns and burner
- Heat prove mat
- Tripod
- Clamp stand
- Scissors
- Goggles
- Gauze
- Measuring cylinder
Diagram
I will set up apparatus as shown above in the diagram. Then I will sand the magnesium until it shines (I will get rid of magnesium oxide) so that I can cut it into pieces. I will cut it into 15 pieces of 1 cm. The acid will be measured as we go along to. The volume of the acid, as I decided in the preliminary work, will be 50 cm². This will be measured using a 100 cm² measuring cylinder and then purred in the small beaker. It is going to be kept by a clamp stand so that the acid level would be lower then the water in the water bath. The large beaker will act as a water bath, and will be standing on a tripod and gauze so that it heated easily using buns and burner. It will be used to heat up the hater bath to make the acid the needed temperature. Also I will also put a heat prove mat under the tripod and the buns and burner. The starting temperature will be 25ºC, from the experiments I did before I know that this is the temperature of the water from the tap, so I will not have to change the temperature for the first temperature. I want to have as much data as possible so I will work out the rates for at least five temperatures. So that I will not have to heat up the acid to a high temperature I only go up in 5ºC every time. I think that I will have time to get through at least five temperatures, so the highest temperature will be 45ºC. Also I will need 2 thermometers, one to measure the temperature of the acid and another one to measure the temperature of the water bath. This will be needed to make sure that the water bath is not warmer then the temperature required, so the experiment will be fair. Also the thermometer in the acid will be used to suture the acid and keep the magnesium ribbon in acid, not floating. I will start with the smaller temperatures and then go on to bigger temperatures, so that I will not have to wait fro the water to cool down. The method that I will use to measure the rate of reaction was chosen in our group to be the timing. This is because it is the fastest to do and requires the least equipment. So we will time it will take the reaction to end. This method is described in detail in ways of following a reaction. The stop watch will be operated by one member of our group and another one will suture the acid with magnesium. I will do three repeats for each temperature to be able to do averages and see anonymous results. This graph is just before the analysis section.
Health and Safety
Health and safety is important during any practical and it is slightly different for each practical. The point below are general but still fill be followed all the time trough the practical.
- Do not sit down at any time during the experiment. It is better to be able to getaway from the reaction if something goose wrong.
- Wear goggles when working with acid and fire.
- Rinse any acid that gets in the skin.
- Do not play with fire it is dangerous.
- Do not boil the acid and use the water bath.
- Keep the magnesium away from fire.
Results
I followed my plan during the experiment and I resaved some good results. They are below in a table. I have included the column for rate, it converts the times to rates of reaction. The only difference from my plan was that I did four repeats instead of three.
The value that is written in grey is an anonymous result. This is because it is different from all the other times for this temperature and stands out from the rest. The repeat number 1 for starting temperature f 25ºC is the anonymous result. I also drew a graph to represent this data (see next page). On it I plotted the rate of reaction at different temperatures. Temperature is a controlled variable, so it is measured up the x-axis and rate of reaction is the dependant variable and is measured up the y-axis. I also decided to measure the end temperature, the temperature which the acid was at straight after the reaction ended. On my graph I have circled the point, that did not fit in with the pattern of the others. This is an anonymous result.
Analysis
In my results I can see that the temperature is linked with rate of reaction. From the line on the graph I can see that when the temperature rices the rate of reaction rices too. This pattern could be explained scientificly, especially if looking to what happens to the molecules when the liquid reactant is warmed up. The increase in temperature is an increase in the energy that each individual molecule has on average. The increase in energy that molecules have is what makes the move round faster. For the magnesium and the hydrochloric acid a hydrochloric acid molecule must hit the magnesium molecule, the magnesium molecules do not move, its a solid. Also the speed at which the molecules collide should be a certain a speed or bigger. This is called an 'effective' collision. The increase in temperature increases the number of molecules that have the speed enough to make an effective collision, therefore the probability of effective collisions increases. The heat energy is the average speed at which the particles move, therefore increasing heat energy will increase the speed of an average molecule and this the collision frequency. The energy that is spend to heat the substances can only be used to increase the speed at which the molecules go, so substances with higher temperature must have the molecules moving faster. Probability of more effective collisions will always be similar to the reality, because there are a great number of molecules in a substance and the higher the number the more likely that the higher probability will increase the actual number of effective collisions. More effective collisions mean that the rate of reaction will increase.
The theory of 'Maxwell Boltsman' too explains how the rate of reaction increases after an increase of temperature. I have drawn a graph that helps to explain it. This is general and dose not have any numbers on because it could be interpreted for any reaction including the one we are studying. The graph shows curves for different temperatures, one 20ºC and another one 30ºC. It also shows the different numbers of molecules that are any given temperature. The curves show the same reaction, so the number of molecules/ area under the curves is equal to each other. The difference is in how it is distributed. The highest point in the curve is where the most molecules are and the most molecules in 30ºC have a higher temperature. However we are especially interested in the molecules that have a temperature enough or higher energy to make an effective collision. It could be clearly seen that the numbers of molecules is higher for the 30ºC curve then for the 20ºC. The area equals to the number of molecules and it is shaded in pencil for the 20ºC curve, and the area under 30ºC curve is shaded with blue lines. It could be easily seen the the area shaded in blue covers all the pencil shaded area and extends beyond that. Also it is roughly twice as big because the temperature is a ten degrees rice. This theory is backed up by many experiments and is scientifically proven. I did not generalise the temperature because it is also important to see that their is a ten degrees difference. Rate of reaction depends on the number of molecules that have sufficient energy to make an effective collision' more particles- faster rate of reaction.
I want to also see how a ten degree increases changes the rate of reaction and if these results agree with my prediction. To see the change I will need to do some calculation and a results from a temperatures with a difference of ten. For example I will pick 35ºC (31.9) and 45ºC (46.8). To calculate the increase in percentages I did the next calculation.
46.8/ 31.9* 100= 146.7%
This means that the increase is only 46.7%. This is the same as the increase of 1.467. This dose not agree with what I investigated in my prediction. This is the research I have done about a ten degree rise. It is proven that this doubles the rate of most reactions. This reseasurch was done in the internet, the firs useful website that I have found was:
“http://scidiv.bcc.ctc.edu/wv/7/0007-005-rea-t-cat.html”
Under the following title the above was clearly stated.
“Collision theory and temperature effects on rates
Reaction rates are roughly doubled when the temperature increases by 10 degrees Kelvin.”
To convert it into numbers and be able to compeer this with the increase I can say that to double something is the same as timing it by 2. This is differnt to what I found I my practical results. To see if my increase was stable I picked another 2 results- 25ºC (23.7) and 35ºC (31.9).
31.9/ 23.7* 100= 134.6%
The number is slightly different to what I saw before with my results and even more different to the double increase that should happen in theory.
