To find out what happened to the hydrochloric acid when mixed with different concentrations of sodium thiosulphate we needed to carry out an experiment, for this experiment we would need ; 1 Clamp 1 Blue Cross 1 Burette 1 Conical Flask and 2 beakers to store the chemicals 1 measuring cylinder and 1 stop watch to time how long the reaction took. We chose the equipment because it is easy to use and has a greater percent of accuracy than any other equipment. We used a burette becuase it i the most accurate way of measuring out a particualr amount of liquid wheter its a chemical or just a water comparing this to a measuring cylinder that goes up in 1mm³the burette is still far more accurate as we can ensure every drop of chemical is released out of the burette however for the measuring cylinder we cant guarantee all of the chemical will come out and we would be left with little drops in the bottom, although they are only little drops left it does effect the reaction speed.
Diagrams of Equipment
Method
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Measure the specific amount in this case 10cm³ of sodium thio (Na2S2O3) and 40cm³ of water.
- We then poured the hydrochloric acid steadily into the burette.
- Following this we gently released the acid from the burette into the sodium thio and water solution.
- Placed a beaker with the hydrochloric acid, sodium thio and water solution onto the cross.
- Once the solution went opaque we stopped the stop watch and then recorded the results into our table (shown below) We used the same person each time on the stop watch and on the viewing of the cross to make sure it was a fair test as if we changed person each time the other person may have better eyesight.
- We then thoroughly washed out the reaction vessel and repeated the experiment to make sure the first one was accurate and recorded these results into our table also.
- Finally we repeated the experiment but this time using different concentrations of sodium thio and water and recorded these into our table also.
Variables
The independent variable in this experiment was the concentration of each solution for example we once had 10cm³ of sodium thio diluted into 40³of water, we changed this every time for example on another occasion we would have 20cm³ of sodium thio and 30cm³ of water.
We can’t control the dependent variable which for example would be the conditions e.g. temperatures of the room we carried out the experiment in this could effect the independent variable in many ways for example it could speed up the rate of reaction or even slow the rate of reaction down we don’t know and unfortunately we couldn’t control it.
The controlled variable in this experiment was the amount of water and sodium thio solution used each time.
Anomalous Results Table of results for main investigation
What my reactions did
The changing concentration of sodium thiosulphate affects the rate of reaction with the hydrochloric acid;
Chemical Equation 2HCL + Na2S2O3 the reaction would reach its end point quicker if it was like this 2HCL + 3Na2S2O3 .
I found that when there was a strong concentration of the thiosulphate the acid reached its end point quicker than it would if there was a weaker concentration of sodium thiosuplhate this would simply happen as there is more thiosulphate to diffuse quicker therefore making it reach the end point quicker.
Analysis
Graph Analysis
As you can see from my graph showing concentration of Na2S2O3 vs Time, x is inversely proportional to x as time decreases the concentration does also and it has negative correlation. The scatter at towards the higher concentration is generally good, however points 40cm³ 50cm³ were outliers but after repeating the experiment we realized it wasn’t and these two plots just didn’t fit the line of best fit and the line bisected the two point well, at first we thought this result may be an outlier but after repeating the experiment we realized it wasn’t. However on the graph shows Rate of Reaction of different concentrations my correlation was positive this graph, like the other also had a good scatter and shows m=y/x well. There was one definite outlier on this graph; the last plot was way of the line of best fit this could be due to many things such as, Human error during dilution of solutions and contamination of glassware. To improve this graph we should really repeat the experiment again for the last point. While analysing the graphs I found the range bars were very small, this is generally a good sign as the results for both experiment were very similar with no huge difference.
Analysis of data
In my data nearly all of my results were within 2 seconds of each other showing the experiments were fairly accurate and reliable, however there were a few anomalous results in my data which I highlighted above because we had these anomalous results we carried out a third experiment on the two results that were faulty after doing this we found this new data fitted the trend much better, these first anomalous results could be due to the simple fact of human error.
Conclusion
By looking at the results and the graph that we have drawn and gathered from the experiment it is easy to see that changing the concentration of sodium thiosulphate affect the rate of reaction with hydrochloric acid. From the results it is possible to say that increasing the concentration of sodium thiosulphate increases the rate of reaction with hydrochloric acid. For example, when there is 10 ml of sodium thiosulphate, mixed with 40 ml of water, and 5 ml of hydrochloric acid is added it took a mean time of 217.4 seconds to react. When 50ml of sodium thiosulphate and 5 ml of hydrochloric acid is added it only took a mean time of 36.11 seconds for the reaction to occur. When I drew my graph I used the calculation 1000/ the amount of time (S). Therefore if the time for the reaction took only a second, I would use the calculation to get 0.001. This gave much smaller numbers to work with which is easier and also means I can be more accurate with the drawing of my graph. This shows that increasing the concentration makes a large difference in reaction times. There are several limitations to my results, one being that not many repeats were carried out of the experiment. Doing this could substantially strengthen the confidence in my results and increase the reliability of my results. However, we did not have enough time to do this so we only repeated the experiment twice and a third time if there was a big difference in the two results. Also there are a couple of results on the graph that do not fit the line of best fit; this is at 0.5 Molar on my molarity versus time (S) graph. This could be the result of a little bit too much HCl being added to the solution. It could also have been due to the timing being slightly incorrect; this then makes the rest of the work slightly wrong therefore ending up with an outlier on the graph. My other outlier was on my other graph; the concentration of sodium thiosulphate vs. Time, this graph had an outlier at 0.15 M. This outlier is quite far from the line of best fit and should be repeated again in another experiment. I think that there could have been a number of errors made here therefore repeating the experiment for this molarity would be the best idea. My results are first order kinetics because as the molarity of the solution increases, so does the reaction time. My graph also shows that there is a positive correlation and that the results are proportional because as x increases, y also increases. First order reactions mean that as the rate of reaction doubles, so does the concentration. At 0.05M the rate of reaction was 2 S-1, at 0.1M the rate of reaction was 3.6 S-1. This means that as the concentration doubles the rate of reaction almost doubles as well. However, I think that with more experiments and with the improvements I suggested earlier, I think that the rate of reaction would double when the concentration of the solution does. I can also prove this by working out the gradient: m= y/x. The gradient of my graph was 1.3. There is a large increase in the rate of reaction between 10 ml of sodium thiosulphate and 20 ml of it. However, there was only a small increase in the rate of reaction between 30 and 40 ml of sodium thiosulphate. The results could be improved if more experiments were carried out because we could eliminate more anomalous results that occurred which would give very reliable results.
