Newer Science Reaction

Karl Rollason, 11RLE Science, Mr. Davenport

Reaction of sodium thiosulphate and hydrochloric acid GCSE Investigation. The Reaction…. . •Sodium thiosulphate, Na2S2O3 reacts with HCl to give a reaction mixture that gets cloudier as yellow sulphur is formed. •Na2S2O3(aq)+2HCl >2NaCl(aq)+S(s)+SO2(g)+H2O(l)

When hydrochloric acid is added to the sodium thiosulphate a reaction occurs which produces a cloudy suspension of solid sulphur. The time it takes for the cross to disappear can be used to investigate rate of reaction Equipment: •Laminated paper with X on it •Beaker/test tube •1M, Hydrochloric acid •0.2M, Sodium Thiosulphate solution •Conical Flask/Beaker •Stopwatch Method We will measure the time taken for a cross beneath a reaction flask to disappear due to the liquid in the reaction becoming cloudy. We will do the reaction with several concentrations of hydrochloric acid and try to work out the rate of reaction. Normally the reaction that we are trying to change is done in a flask. First of all you stir 50cm3 of sodium thiosulphate and 10cm3 of hydrochloric acid into a flask containing water and when the three are mixed together you start the stopwatch. After making sure the chemicals are properly mixed together I will place the flask over a piece of card with an x on it and time how long it takes for the x to be no longer visible. The independent variable will be the amount of sodium. I will repeat this experiment 2 more times to ensure I have a more accurate reading. Then I will change the amount of water, adding by 2cm3 each time and subtracting the HCl by the same amount each time. I will change the concentration of Sodium Thiosulphate (decreasing the concentration of the substance in solution means that there will be fewer particles per cm3.) The fewer

Karl Rollason, 11RLE Science, Mr. Davenport particles that there are in the same volume the further away from each other the particles will be, therefore the reaction would be slower. Collision theory background

This is what the experiment looks like at 3 different stages, the 1st being before the reaction has started the 2nd being when the reaction is taking place and the 3rd being when the reaction has taken place. Picture reference= Made by me on my computer using paint.

Karl Rollason, 11RLE Science, Mr. Davenport

The investigation. In this investigation we will be looking at how concentration can affect the rate of this reaction. We can control concentration by diluting solutions of known strengths HCl (ml)

Na2S2O3 (cm3) 50cm3

Water(cm3) 0cm3

50cm3

2cm3

50cm3

4cm3

50cm3

6cm3

50cm3

8cm3

10ml 8ml 6ml 4ml 2ml We attempt to repeat this reaction 5 or 6 times, we do this because the more times we repeat it, the results will become more reliable than if we had done it only twice or three times, also if we wanted a lot more accurate results, we would repeat the reaction a lot more times as there will be a better average.

The Effect of Concentration Is: •The concentration of a solution is how strong the solution is. For example, if we consider the reaction between marble chips (calcium carbonate) and hydrochloric acid: •calcium carbonate + hydrochloric acid —> calcium chloride + water + carbon dioxide •Then a stronger acid contains more acid particles and less water particles than a weaker acid. •Increasing the concentration of a solution leads to more collisions (greater frequency of collisions) so the rate of the reaction goes up. •In a less concentrated acid, the number of collisions is low, so the rate of the reaction is slower. (The water particles aren't shown): •The effect of temperature

Karl Rollason, 11RLE Science, Mr. Davenport •When we increase the temperature at which a reaction is taking place, the particles move more quickly. This has two effects: Collision Theory More collisions take place. When a collision occurs, there is more chance that the collision will lead to a reaction, because the amount of energy is more likely to be greater than the minimum amount of energy needed (the activation energy) At a lower temperature, the number of collisions is lower because the particles are moving more slowly. Also when a collision occurs, there is less chance of a reaction taking place because the movement energy in the particles is less (in the animation successful collisions flash yellow, unsuccessful collisions flash blue): The effect of particle size: Solids with a smaller particle size (e.g. powders or small chips) react more quickly than solids with a larger particle size (e.g. large chips). Here is why: Look at these diagrams;

The perimeter of the large chip is 12 units. The acid particles can only collide with the edge of the chip. However, if we break up the large chip into 9 smaller chips: Then the perimeter around each chip is 4 units, but there are 9 of them so the total perimeter is 4 x 9 = 36 units. Notice how the acid in the second diagram can reach what used to be the centre of the large chip. Adding a catalyst: A catalyst is a substance that speeds up a reaction without being used up itself. Some reactions have catalysts that can speed them up, but for many reactions there is no catalyst that works.

Karl Rollason, 11RLE Science, Mr. Davenport Here is an example of a reaction with a catalyst. Hydrogen peroxide decomposes (falls apart) to form water and oxygen gas: Hydrogen peroxide —> water + oxygen This reaction only occurs very slowly unless we add the compound manganese oxide that acts as a catalyst for this reaction. When the catalyst is added the reaction speeds up greatly but the manganese oxide never runs out

Background Information Ref. = http://www.sciencepages.co.uk/keystage4/GCSEChemistry/m3ratesofreaction.php

Prediction I predict that in the experiment because of the fact that more water is added and less hydrochloric acid is added that the time the reaction will increase. I also predict that there will be a positive correlation between the results as when more water is added and when less HCl is added the average of the time taken for the reaction to finish will decrease by roughly the same amount every time. I predict that half of the amount of acid will produce half of the reaction rate. In my results I will look for obvious outliers that are likely to ruin my experiment and extract them. Due to the experiment not being performed under ideal circumstances, the results I record may not be 100% accurate however I will personally do my best in order to make sure all the factors of the experiment are in order and that none of the items in the area that are not part of the experiment will be kept well away. ANALYSIS OF RESULTS These were my results:

Karl Rollason, 11RLE Science, Mr. Davenport HCl (ml)

Na2S2O3 (cm3)

Water (cm3)

50

0

10

Ex. 1st 2nd 3rd

Time Taken (secs) 36 34 35

8

Av. 1st 2nd 3rd

35.00 38 38 39

6

Av. 1st 2nd 3rd

38.33 41 44 44

4

Av. 1st 2nd 3rd

43.00 49 48 51

Av. 1st 2nd 3rd

49.33 63 66 65

Av.

64.66

50

50

2

2

4

50

6

50

8

Conclusion The basic pattern of the results shows that the more water that was added to the formula the longer the reaction took. In conclusion I feel that my prediction matched with my results and I feel they are relatively accurate, there were no outliers. I also predicted that as more water was added and the amount of HCl added was decreased that the time taken for the experiment to end would continuously increase at a steady rate and as you can see at the graph above, this was an accurate prediction. Evaluation Personally I feel that the experiment went quiet well. We can assume that no errors occurred during the experiment due to there being no outliers. The equipment that we used was accurate to 0.2ml, although I do not feel that more accurate equipment needed to be used and I feel that my results were as accurate as they could be considering the equipment. The results from my experiment prove that I was right in predicting there would be a positive correlation as also shown in my graph that the more water added and the less HCl added the longer the reaction would take. Due to the fact their were no

Karl Rollason, 11RLE Science, Mr. Davenport outliers in my results, we can assume that during the experiment that I did not measure anything wrong and each liquid was correctly measured. There are several possible errors that could have gone wrong in this experiment, for instance, there could have been errors in the measurements or possibly faulty equipment. There can also have been errors as there is a low temperature and when it gets to the end of the experiment it is not easy to judge. Also there could have been errors through no fault of the equipment but as they are not completely accurate, the amount of error can be calculated by the formula: error % = error/range x 100. Therefore the error range in this example is 0.2/50x100=8%. However I don’t think this should be looked into too much considering the numbers are insignificant. The fact that none of these errors did go wrong obviously shows I made an effort to make sure the measurements of liquids were right. Other problems that could have gone wrong are as the experiment was not performed under ideal circumstances, other experimenters may not have taken the experiment as seriously as me and my partner did and they may have accidentally ruined our experiment by being foolish and distracting us and causing us to use wrong measurements. Also personal items may have slightly affected our experiment as they may have gotten in the way. As you can see on my range bar graph my results all seem to be very accurate. The space in between the highest and lowest bars is very small proving that my results are accurate. The result of having too much or too little of each reagent is that it will change the times of the reaction.