Rate of Reaction

Fair Test

There are many different variables that may affect my experiment; these variables are…Volume (cm³): I will keep the volume the same because the higher the volume the faster rate of reaction. This is because if the volume increases so will the number of hydrochloric acid molecules, this will cause more collisions that are successful increase the rate of reaction.

The variables that were controlled were:

• I controlled the amount of solution to 50ml because if we used too little the magnesium might not be fully dissolved and would stop. I made sure of this my measuring it in a measuring cylinder and reading the measurement from the meniscus.
• The temperature was kept at room temperature because if it was cooler it would slow down the reaction and if it was faster it would speed it up. I made sure of this because the entire experiment was done in the same room.
• The surface area of the magnesium was kept 30mm, because the mass has a bigger affect. The size of the magnesium ribbons should be the exact same. If this wasn’t done there would be a huge difference in our results because the experiment would’ve not been carried out correctly. I made sure that the ribbons were 30mm by measuring them accurately with a ruler.
• Time measurements in between was kept to 15 seconds because if we had a different number of seconds before we marked down what it was it would be more difficult to make a graph and it would be less accurate. I made sure of this by recording the measurements at the exact time. However there could be errors due to the stopwatch’s battery.
• The hydrochloric acid had to be the same because if we used another bottle, there would have been chances of it being tampered and our experiments would end with incorrect results. I made sure of this by only using the bottle we were provided with.
• All the apparatus- the flask, the gas syringe, the stopwatch, the delivery tube, the clamp and the measuring cylinders would have to be the same for it to be a fair test. I made sure of this by using only the equipment provided.

All the variables above were controlled because they would make the test successful and balanced. However there would always be 1 independent variable in an experiment. In this case it is the concentration.

The only independent variable was:

• The concentration which I was testing was changed to find what effect it had on the rate of reaction.

Collision Theory

Collision theory qualitatively explains how chemical reactions occur and why reaction rates differ for different reactions. It assumes that for a reaction to occur the reactant particles must collide, but only a certain fraction of the total collisions, the effective collisions, cause the transformation of reactant molecules into products. This is due to the fact that only a fraction of the molecules have sufficient energy and the right orientation at the moment of impact to break the existing bonds and form new bonds. The minimal amount of energy needed so that the molecule is transformed is called activation energy. Collision theory is closely related to chemical kinetics. In this case we are using magnesium and hydrochloric acid and we can see them reacting.

The collision theory is when particles collide with each other for a reaction to take place. Particles are in constant movement. They move rapidly in all directions so millions of collisions occur each second which will lead to a reaction. Reactions can only take place when different particles hit each other however the reacting particle does not only need to hit the other particle, they have collide into each other with sufficient energy otherwise they will not react.  In many reactions the reactant will not be converted into a product unless it is temporarily given some extra energy, this is called activation energy.

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Preliminary work

My preliminary work was on concentration and I was investigating the rate of reaction between a magnesium and hydrochloric acid. To prepare the investigation, I decided to do some preliminary investigations, so I would get a good, balanced range of concentrations to use. 

By doing this, I found that I should use 0.6 to 2 molar acids for my investigation, as anything below this would take longer than 5 minutes to react properly with the magnesium, and anything above it would react and wear away the magnesium in less than 15 seconds, so it would be difficult to analyse. I used 0.4 molars concentration in my preliminary investigation to prove that it would be very time consuming to use any concentration under 0.6.

I also found that for the acids under 1 molar, I should check the amount of hydrogen produced every 30 seconds, but when it is above 1 molar, I should check every 15 seconds as the magnesium is worn away a lot quicker. However further on in my investigation I decided not to do that because I want to see the changes in reactivity.

This table shows the amount of hydrochloric acid and water needed to make a dilution. As I only used 50ml of the dilution, each concentration should have 50ml of liquid.

Later on in the investigation I decided not use 0.4 because it was time consuming.

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Safety

In an experiment safety is very important and the people participating in the experiment need to be very safe of the environment there in. In a laboratory there are harmful, corrosive and dangerous chemicals that could have a long-term effect on the victims. This experiment didn’t include corrosive or dangerous chemicals, however anything could go wrong at anytime.

There are many safety precautions that I have to take before I start my experiment. To make sure my test is safe I will be wearing goggles, especially when handling the hydrochloric acid as it is corrosive so I have to make sure it does not go into my eyes as it can damage my eyes. I should also be wearing gloves because hydrochloric acid can damage my skin tissues as it is corrosive. I will also try to make sure that the hydrochloric acid keeps away from the edge of the tables so it does not fall. Also I should try keeping the surrounding area clear and making sure the bags are tucked underneath the table so nobody will fall, especially when carrying hydrochloric acid or glass materials.

To protect my eyes, I wore goggles at all times during the experiment. The goggles protect your eyes incase of acid splashes. Another safety precaution we followed was that we moved all unnecessary equipment such as coats and bags away from where the experiment was taking place. This would make sure nothing came in our way during the experiment and would also keep our belongings safe. With this we could concentrate on the experiment and reduce the chances of an accident.

Also, we made sure not to be too close to any other group who were working because there was a chance that we could be getting in the way or that if some one has an accident it doesn’t affect our work or if we have an accident it doesn’t hurt others.

In addition, we had to stand up at all times during the experiment. This was because if an accident was to have happened we could move away from it faster then f we were seated. Another safety procedure that I followed was that during the experiment, I set up all the equipment in the middle of the table so that nothing would fall of the ends. The last safety thing I did was tie my hair back so it didn’t come in the way. Hair is flammable so if anything was to catch fire, my hair would be burnt.

Accuracy of Measurements

To make sure my experiment will be accurate I will make sure I measure the amount of Hydrochloric acid as accurately as possible by reading the lower meniscus. I will also be using a digital stopwatch, which will make the readings more accurate as it will be to the nearest millisecond. I will also try and read my readings as accurately as possible and will also make sure the syringe is completely in before every experiment. One more final thing that I will do to make sure my experiment is accurate, I will rinse out equipment to make sure I do not have any excess Hydrochloric acid remaining in the beaker or any of the products remaining every time I have finished using the equipment/before each experiment as this will affect my experiment.

Many precautions/methods/apparatus were used to measure quantities accurately.

• A ruler was used to measure the magnesium strips. The ruler was very accurate and easy to use because of its straight edge. The strips were measured in millimetres (mm). Each strip had to be 30 mm in length. I would line the strip against my ruler, score a line with my pencil and then just break it off because the magnesium would be so thin.
• A measuring cylinder would be use to measure liquids precisely. In this experiment I use measuring cylinders to measure hydrochloric acid and water. Both would be measured in millilitres (ml). The reading would be pretty accurate because the measuring cylinder would read the measurement from the meniscus. However there was 1 disadvantage that I have noticed. This was that when I had poured the liquid into the flask, there would still be a tiny some of remains, which would affect my results slightly.
• The gas syringe is also an apparatus that would measure a quantity. The gas syringe would measure the amount of hydrogen produced when magnesium would react with hydrochloric acid. The quantity is measured in volume (cm3). It was pretty hard to read of because it would constantly move at a random speed. During the preliminary test my gas syringe was blocked at time and this made my result very unreliable.  
• The stopwatch was the final apparatus used to measure quantity. The stopwatch is measured in seconds/minutes. It wasn’t difficult to use because the readings were clear. However, the stopwatch can be inaccurate. If the battery is dying out then the stopwatch doesn’t perform to its full ability and if I was using a stopwatch that lacks energy then my results would be unreliable.

Reliability of Method

To make my method and the test more reliable I decided to repeat the experiment. This would show me if there are any errors in my experiment.

In experimental sciences, reliability is the extent to which the measurements of a test remain consistent over repeated tests of the same subject under identical conditions. An experiment is reliable if it yields consistent results of the same measure. It is unreliable if repeated measurements give different results. It can also be interpreted as the lack of random error in measurement.

Using this knowledge I saw repeats as a way of making my test more reliable. Also I had to see whether my other test gave similar results to each other, if they did it would show that my test was reliable.

To make sure my experiment is reliable I will carry out at least 8 different readings using 8 different concentrations. For each concentration I will have at least 2/3 different readings ensuring that I will have enough points to make sure my graph is reliable and that I will be able to interpret it. It will also be clear with this number of points on my graph, whether I have any anomalous results – making it easier for me to know where I have gone wrong. Another important thing to make sure my test is reliable, is to repeat my experiment at least twice. This will help me to see if my readings are accurate; if there is a huge difference between my 1st and 2nd reading I will repeat it again until I have two sets of similar readings. If I have more time left I will repeat my test one more time to make sure it is reliable.

Results/Data- A table to show the rate of reactivity as the concentration increases.

This table shows my results when I first carried out the test after I had completed the preliminary work. This experiment was successful as I had results that were similar to the results from my preliminary work. In ‘red’ I have highlighted where the magnesium had disappeared and the reaction had finished. In ‘yellow’ I have highlighted the point where I stop the reaction because it was time consuming and would stop me from completing the whole experiment. This only happened once, at [0.6] molars. It would take another 5 minutes to complete the reaction and because I was short of time, I stopped the reaction; however I decide to include its results in my final table because I had to show that I had carried out the experiment with concentrations lower than [0.8].

In my preliminary result I had carried out an experiment to see how long the reaction would be in 0.2 and 0.4 molar. Through this I understood that it would take far too long if I used them In my real experiment.

I believe that my results are accurate and reliable because for 0.8-2 molars, the amount of hydrogen produced for each concentration would be around ‘41’.

Repeated Test

As in my first table, I have highlighted in the colours red and yellow the point where the reaction ad finished or when I forced it to an end. I had repeated my experiment to see if my result were reliable and I had done the experiment correctly. My results still could be incorrect due to me not recognising what I had done incorrectly throughout the experiment.

If the tables are unclear, they read horizontally at the top, the concentration used. The first column read the time in seconds and my results show how much hydrogen was produced every 15 seconds.

This set of result are reliable, however they the first set of result are more to be right because this had a greater range of hydrogen produced- 40-44. The range is 4cm3. This may not seem big but it does affect my experiments and my results.

Now I am going to compare my two sets of results and draw graphs to represent the data. I will all use this data to find the mean and pot a line of best fit.

Graphs

Analysis

Now that I have drawn my graphs I will analyse them. While doing my graphs I notice that there weren’t any outliers which made my experiment very reliable. It also showed that the polynomial trend-line on each graph had a very good curve and it was reliable because all the curves were similarly shaped.

Each graph has a similar curve showing my result was done accurately and it was done using the correct amounts of hydrochloric acid. Also my graphs showed consistency as all the curve of best fits are plotted in the in a small range of area.

Looking at the graphs of the different concentrations I can see that as the concentration increases the time of the reaction decreases. This shows that the rate of reaction is increasing as the concentration increase portrayed by fact that as each graph becomes steeper.

I can also see this pattern when looking at the rate of reaction graph I can see that this graph has a positive correlation, again allowing me to perceive that as the concentration increases so does the rate of reaction. This is supported by scientific knowledge because as I said before when a substance is has an increased concentration, the particles move faster increasing the rate of reaction as the chances and number of collision increases.

In relation to my aim I have found out that changing a variable does cause the change in my result. For instance, in this project I have changed the concentration of hydrochloric acid and this has showed me that the higher the concentration of the acid the faster the reaction happens. Now if I was to do another experiment I would change another variable (the length of the magnesium strip) to whether or not it affects the rate of reactivity. I would predict that the longer the magnesium strip was the longer it would take for the reaction to finish.

Evaluation

Now I am going to evaluate my experiment. Here I will decide what improvements could be made to it, the pros and cons of the experiment and I will summarise my experiment.

I could have thought about using better equipment, which would give me more accurate and reliable results. I could have narrowed my check time from 15 seconds to 10.

I could have use a better spread of concentrations. Instead of u 0-2 molars, I could have a bigger range. Maybe I could have found the results of more concentrations between 0 and 2 molars. For instance I could have worked on finding out the rate of reactivity of 0.1, 0.3, 0.5...

The pros of my experiment were that I finished with accurate and reliable result. I had come to a conclusion about the rate of reactivity and I had understood how changing a variable could lead to a change in the results.

The cons of my experiment were that I hadn’t looked further into my experiment. This was because I didn’t have much time to narrow the concentrations.

To evaluate, I can say that this experiment went well. I think that my test has been fair, as I have used same lengths of the magnesium ribbons and the same equipment for every test. I have obtained at least 2 different measurements for each different concentration, using the same method. On top of that I have made sure that I have collected readings for at least 8 different concentrations to give me stable readings for my rate of reaction graph. Overall my curve of best fit fits into all my graphs and are stable and there no anomalous results. The concentrations that I had experimented were 0.6 molar, 0.8 molar , 1.0 molar, 1.2 molar, 1.4 molar, 1.6 molar, 1.8 molar and 2.0 molar. I have tried to make sure that I measured everything accurately.

To make sure my results were accurate; I made sure I measured from the lower meniscus every time I measured the hydrochloric acid/water to make sure that I don’t add to little or too much hydrochloric acid/water so I can get the exact measurement of what I had measured. I also made sure that I washed the beaker properly every time I did the experiment so there will be no excess reactant left behind. This will make sure that there will be no products or reactants left behind to affect the experiment as it may react in the next experiment if there were any excess hydrochloric acid or water. I also tried to make sure that I read the scale reading on the gas syringe every 15 seconds on the dot, as the gas continues to flow so I had to read the reading as soon as possible to get accurate results. I had also made sure the syringe was completely in before every experiment to make sure the test is fair.

 

I could have improved my experiment by having quicker reflexes, which would have made my results even more accurate, as I could be faster at reading the readings on the gas syringe, giving me exact result every 15 seconds. If I had faster reflexes I would have had more accurate results.

To make sure my results are reliable I made sure I repeated the experiment atleast twice until I got two sets of readings which are similar. I have also collected enough readings to make sure that my graphs can be reliable and that it will allow me to make a reliable conclusion. However I could have made my experiment more reliable by increasing the number of readings and also by increasing the number of different concentrations I have investigated, as there will be more results to give me a consistent line/curve of best fit, plus this will make my readings more reliable as there will be more evidence if whether my results will fit onto my graph or not and whether all concentrations follow this rule. I can also see if this works with very small concentrations or not. I could have also increases the number of times I repeated my test at least one more time to make my experiment more reliable for example to have three sets of similar results for each concentrations.

Overall to summarise, I felt that my experiment was a success because I met my aim and ended of a good sets of results and a conclusion about rate of reactivity.