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The aim of this coursework is to investigate the rate of reaction between sodium thiosulphate solutions and dilute hydrochloric acid.

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GCSE CHEMISTRY COURSEWORK Aim The aim of this coursework is to investigate the rate of reaction between sodium thiosulphate solutions and dilute hydrochloric acid. Introduction In this investigation, I am going to be looking at the reaction between sodium thiosulphate and hydrochloric acid. When they react, a yellow precipitate of sulphur is formed. The diagram below shows the different stages of the reaction taking place. This reaction can be timed by measuring how long it takes the precipitate to make the mixture opaque. Solutions are mixed together Precipitate is formed Solution is now opaque The word equation and formula for this reaction is: Na2S2O3 (aq) + 2HCl (aq) ? 2NaCl (aq) + S (s) + SO2 (g) + H2O (l) sodium thiosulphate + hydrochloric acid ? sodium chloride + sulphur + sulphur dioxide + water Rate of Reaction The rate of reaction is the speed of the reaction between two particles. It is how quickly a reaction takes place. The rate of a reaction can be measured by measuring the rate that a reactant is used. Temperature, concentration, pressure of reacting gases, surface area of reacting solids and the use of catalysts are all factors which affect the rate of reaction. Chemical reactions can only happen if the reactant particles collide with enough energy. The more frequently particles collide and the greater the proportion of collisions, the greater the rate of reaction. There are two ways to measure the rate of a reaction: * Measure the rate that a reactant is used up * Measure the rate that a product is formed The method chosen depends upon the reaction being studied. Sometimes it is easier to measure the change in the amount of a reactant that has been used up, and sometimes it is easier to measure the change in the amount of a product that has been produced. The measurement itself depends upon the nature of the reactant or product: * The mass of a substance (solid, liquid or gas) ...read more.


With a more concentrated acid, the number of acid particles is greater, so the number of collisions is greater and the rate of the reaction is faster. Equipment List 250 ml Conical Flask - where the reaction will take place. 10ml Pipette - to measure the amount of HCl needed (10ml) precisely. It is more accurate compared to a beaker or measuring cylinder. Pipette Filler - this is attached to the pipette. 50 cm3 Burette (x2) - this will accurately measure the various volumes of sodium thiosulphate and distilled water. It is more accurate compared to a beaker or measuring cylinder. 100ml Beaker (x2) - to leave at the bottom of the burette, so that the various solutions can be collected. Paper Marker Pen Goggles Stop Clock 630ml of 0.15M Sodium Thiosulphate Solution (Na2S2O3) 180ml of 0.1M Dilute Hydrochloric acid (HCl) 450ml of Distilled Water (H2O) Method 1. Collect equipment and set it up as shown in the diagram. 2. Using the marker pen, draw a cross on the piece of paper. Place the paper on the bench and put the conical flask on top of it. 3. Collect some sodium thiosulphate solution and using the burette, measure 60ml of sodium thiosulphate and put it in the conical flask. 4. Take the pipette and measure 10ml of hydrochloric acid. Pour the acid into the flask and start the stop clock. Time how long it takes for the solution to go opaque, thus making the cross disappear. 5. Record the result and wash out the flask completely, making sure all the solution has been rinsed from the conical flask. 6. Repeat the experiment, using the other volumes of sodium thiosulphate and water, as shown in the blank results table. Make sure the volume of hydrochloric acid remains constant (10ml). 7. Once all the other volumes have been completed, repeat the experiment twice more and record all the results. ...read more.


The use of a measuring cylinder could have possibly affected out results, although it didn't seem to be too drastic. I think that we could possibly improve the experiment by: * Finding an alternative method to using a measuring cylinder and pipette * Finding a way of starting as soon as the reaction starts * Knowing exactly when the reaction has finished; as it was hard to judge precisely when to stop timing. We could possibly use a light sensor. * Varying the number of repeats, to get more accurate results. On the whole, I was not able to find any anomalies, or results which seemed to be odd, although I think that we could look at any individual results to see if we can find any minor anomalies. In order to do this, I am going to plot a graph, which shows all three repeats. This will allow me to compare the results individually, and see if there are any results which stand out. The circled points on the graph are the ones which stand out from the rest of the results. At 0.025M and 0.050M, there seems to be the greatest difference in the set of results, where one result in each case, seems to be separated from the rest. Although, this is the case, the average time isn't affected that much. All the other set of results are more accurate, and the closer together they are, the more reliable they are. Although this is the case, I believe that the results are still good enough to support my conclusion, as these are only minor anomalies. Further experiment I think that we could extend the experiment, by looking at how the other factors affect the rate of reaction, and see what happens to rate of reaction when we possibly have two independent variables, such as temperature and concentration. We could also what the effect of changing the hydrochloric acid is, in a full investigation, although according to the preliminary experiment, it shouldn't make much of a difference. ?? ?? ?? ?? Viraj Patel 10Q Chemistry Coursework Page 1/10 ...read more.

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