New Science, Reaction Of...

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 thiosulphate 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 and when the two 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 Thiosulphate I use each time which will decrease by 10 cm3 each time. When I repeat the experiment I will identify 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 particles that there are in the same volume the further away from each other the particles will be, therefore the reaction would be slower.

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

40cm3

10cm3

30cm3

20cm3

20cm3

30cm3

10cm3

40cm3

10ml 10ml 10ml 10ml 10ml

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. We would like to do this because to get more accurate, not clear conclusions Errors There are several possible errors that could have gone wrong in this experiment, for instance, there could be errors in the measurements or possibly faulty equipment. There can also be errors as there is a low temperature and when it gets to the end of the experiment it is not easy to judge. The devices for measuring volume are at best accurate to 0.2 ml. The result of having too much or too little of each reagent is…….

A

Karl Rollason, 11RLE Science, Mr. Davenport

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 •When we increase the temperature at which a reaction is taking place, the particles move more quickly. This has two effects: 1) More collisions take place 2) 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 this diagram

Karl Rollason, 11RLE Science, Mr. Davenport

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. 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. =

CHANGING CONCENTRATION

Karl Rollason, 11RLE Science, Mr. Davenport ANALYSIS OF RESULTS The basic pattern of the results shows that the more water that was added to the formula HCl (ml)

2 4 6

8 10

Na2S2O3 (cm3)

Water (cm3)

Ex. 1st 2nd 3rd Av. 1st 2nd 3rd Av. 1st 2nd 3rd Av. 1st 2nd 3rd Av. 1st 2nd 3rd Av.

Time Taken (secs)