Investing and measuring the rate of Chemical Reactions
Investigating the rate of reaction by looking at chemical reactions that are taking place. As a class, we looked at many ways to test this and chose one way that was easy to do in which the whole class complete successfully.
1. The rate of reaction is similar to ‘‘speed of change’’. We are constantly looking at our experiment, and when we measure it, the changes taking place is the reaction. Some of the reactions that we know are chemical changes can be seen are such things like bubbles, smells or even boiling. There is more chance of a reaction when there are harder collisions between particles. The change of more collisions means there is a higher chance and higher probability that there will be a reaction. If there is a higher chances of successfully colliding collisions, this means that there will be a thriving reaction happening, so from then on, we are able to measure the rate of a reaction as change is occurring.
2. A reaction can change its rate in many ways. In all of the tests to do this the chemical bonds between substances must be broken and re-made showing the change. One example is temperature. There is a quicker reaction as higher temperate create more energy, therefore creating more collisions to be able to have a reaction. For our experiment we needed to increase the number of successful collisions between the reacting particle molecules. Temperature would increase the collisions taking place, however, for our experiment we did not use temperature to test the rate of reaction as it makes it very difficult, because it makes it hard to get reliable results as temperature can change very quickly.
The moment this happens the pressure and gas given off changes quickly, therefore harder to read. However you could change the surface area to test the rate of reaction, and what this means is to break the solids into smaller pieces meaning a chemical reaction has more particles to work on creating more collisions as there is a bigger space to work on. Although, again, we didn’t use this changeable factor because we wanted to measuring using acid, rather than an area which could we could change as well as being hard to test when the reaction happens. We wanted to keep a factor the same, and in our experiment the Acid, which if we used the Surface Area it would change and we didn’t want this.
Lastly, we could have used a catalyst to test the rate of reaction, however, we decided not to use this variable factor because we were testing the concentration, and by concentration we were testing our rate of reaction by using Molar Acids, so catalyst would have been used in the wrong context.
For our experiment, to test the rate of reaction, we used concentration as our factor. We used concentration because we could create accurate molar solutions that in a way would make it easier to test and give reliable results that could show the rate of reaction. It was a good choice to use concentration as it was easy to measure because gas was made, as this there was a higher change of reactant particles reacting to produce a chemical reaction. We decided to use Quantitive rather than Qualitive because there was no point in using a range of experiments to find out our data, Quantitive was a better option because we could change one thing, in our experiment, this being the concentration making it easier.
We can measure reactions of chemical changes in many ways. The speed of reaction can be observed, by showing how reactions can change to create other substance that form this can be measured. One example is precipitation. This method is where the solution resolves to cloudiness. We measure this until the solid, (in our case being marble) dissolves into this cloudy solution. Although, we did not use this method because it would be hard to measure as you cant pin-point an exact translucent colour of cloudiness or when the solid that creates the reaction disappears as it dissolves into molecules to create the solution. Another way we can measure reaction rates is to measure the change in mass.
When using the mass we measure the speed of reaction that produces gas. When the reaction happens, gas is released therefore the mass becoming lighter, the balance on the scales drops. The faster the balance decreases the faster the rate of reaction. However for our experiment we did not use these methods, we measured the volume of gas given off. In this method we measure the gas (C02) Give off in our 3 minute time period measuring this every 30 seconds. The quicker the amount of gas given off, a faster reaction. The main test for our experiment was to see how fast rate of reaction was and to do this was to see how much C02 would create by how quickly Hydrochloric Acid and Marble Chip could react. The chemical reaction would be ;
CaC03 + 2HC1 = CaC12 + H20 + C02
(Marble)+(Hydrochloric Acid)=(Calcium Chloride)+(Water)+(Carbon Dioxide)
So the method we used for our reaction was the amount of gas given off because with this, we could measure it very easily, using cm3, and by using this it is very accurate. We took a Chronicall flask and placed in it 8 pieces of marble chips (roughly the same size). We had a plunger on the top with at least 20cm of rubber tube coming from the top of it. We had a tub half filled of water that, when we had the burette full of water, we put the tube in the burette and placed both into the tub of water. We did this because C02 would be produced and when it did, it would create air space in the burette being able to measure in cm3 how much gas had been created and how fast because we measure how much water was left in the burette every 30 seconds. We filled the burette with 50cm3 of water as this is how much it could hold.
We flipped it upside down into the tub of water trying not to lose any water and used a stand to then hold it up. One all this has been set up we measured out 10cm3 of the molar acid solution in a measuring cylinder and then poured it into the Chronicall flask. We took the 8 marble chips and once everything had been checked we put the marble chips in and placed a stopper onto the flask. Every 30 seconds, we recorded how much water had been cleared out of the burette as C02 had replaced it. We did this for every molar acid to test the rate of reaction. We could see how long the rate took when there was no more water left to measure.
Before we started our experiment, we did a “trial experiment” to see how we could do this. At first we used acid strengths ranging from 1 Molar acid to 2 Molar acids with 10 Marble chips, however this was unsuccessful. When we did this first, this was unsuccessful because we couldn’t take a measurement and record it because there wasn’t enough time. There was too much gas produced in short period of time, and this is where the majority of the action happened between the ranged of molar acid. If the 2 Molar acids created too much C02, too quickly, it drained the burette. By doing this trial run, we could see what could be changed and see if we could carry on with this experiment. We had to change the range of Molar acid we were using. We changed this from as little as 0.25 molar ranging to 1.25 molar. Not only did we do this, we changed the number of Marble Chips we were using from 10 to 8. This experiment became more successful because the beaker of molar acid had to hit more marble chips to create the reaction.
By looking at my graphs for each of my Molar Acid reactions I can see that some of the experiments we did are different to each other. I can see that 1.25 Molar Acid and 1 Molar Acid start of slow, and then began to go steep. Whereas if I look at 0.75Molar Acid and 0.85, it does the same as the others, where it starts off slow, but the difference with these two experiments is that they have much steeper lines. These two experiments show that they created the most CO2, as it shows that in the time given compared to the other, they had better effects, showing how fast the reaction was. It shows that, by calculating each graph, by taking the amount of gas given off, and then dividing by how long it took to create gives me how much C02 was created given me an accurate account. If you look on the graph, the lines that mark a triangle ,inside that shows how much was created.
If you look at 1.25 Molar, 10cm3 of C02 was created, and this is then the same for 1.0molar acid. If you look at 0.85 molar acid, this produces 12.5cm3 of CO2 and 0.75 creating 20cm3 of CO2 and lastly 0.65 Molar acid creating 12cm3 of CO2. Theoretically, the higher concentration of Molar Acid should have caused more collisions within the particles, but in this experiment 0.85 and 0.75 Molar Acids did. Although, C02 was created with all the substances because each molar acid had to collide with the marble chips with a certain minimum energy, this being the activation energy.
The weaker the concentration, less particles are collide, and the higher, there is more chance and so forth. The molecules have to collide with enough energy, and with concentration, if you go higher, there’s higher activation energy. Each chemical bond needs to be broken, and get them reacting. However, if you look at my results, you can see that the graphs do not show this, they show that the lower strength of Molar Acid had a better effect rather than the stronger solutions, and this reason is explained in my evaluation, where at the same time could be my improvement.
As from my conclusion, theoretically the higher concentration should have produced more CO2, but in my experiment, it was the other way round. Overall, I think my experiment did go well, in terms of getting them all to react. . The apparatus for this experiment could have been better, but then again there wasn’t much we could have done to make this better. For example, when we look at the burette, it was hard to keep 50cm3 as our starting amount of water, because sometimes once you flipped the burette into the water, some water was lost, meaning time was wasted to get it right. Another thing was the flask.
For every time we placed the marble chips into the flask and then added the Molar Acid we would have to place a stopper on the top of it so we didn’t lose some of the gas given off to create a reaction. So somewhere along the line, some gas may have been given off and lost and not counted for possible making our experiment unreliable at some stages, however there is limitations to this, and by looking at my graphs and my results it showed that the reactions didn’t start straight away or they needed time to build up. So in a way you could argue that it was fine with having to put a stopped on as much acid wasn’t lost to create a reaction.
However, I think there was a mistake made in our experiment. Like I said, the higher concentration, there should have been a stronger reaction, but unfortunately this hasn’t shown this. I hold my hands up and say that my experiment doesn’t show the correct data. If you see from my graph that shows how much concentration each molar acid produced, 0.75 and 0.85 are better than the rest and this shouldn’t be happening. Although, I believe there was a fault in our experiment, as 0.75 and 0.85 were different batches, made at a later date, when we needed to add to our experiment to get a better look at the rate of reaction. So therefore, what could have happened is that they were incorrectly concentrated.
I think that, if you look at the anomalies in some of the graphs, there are a few that could have been taken down wrong, or something happened to the experiment, which shows the difference in the error bars that have been plotted and these have been marked on the graphs. However, I don’t think that because of some anomalies that it made the experiment incorrect, because they aren’t too far away from the two other readings that were taken in the class, so I think its ok to say that this wasn’t such a problem.
In all fairness, I think that my conclusion is secure in some places, but not secure, as, in my opinion, the 0.75 and 0.85 batches were incorrectly concentrated, therefore making the experiment at fault. It’s not fully secure because there wer problems, and the 1.0 and 1.25 molar should have produced more C02 as the science explains that the higher concentration equals more of a reaction because there are more collision successfully happening.
I think that if I was to do this again, the definitely, my main problem I would change is that I make all the batches of solutions at the same time and check I have done them all right to make it a better test.