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The aim of this investigation is to see how the concentration of sodium thiosulphate when added to hydrochloric acid affects the rate of the reaction.

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Introduction

Aim: The aim of this investigation is to see how the concentration of sodium thiosulphate when added to hydrochloric acid affects the rate of the reaction. The reaction that takes place is Na2S2O3 (aq) + 2Hcl(aq) S (s)+ 2NaCl (aq) + So2 + H2O Sodium + Hydrochloric Sulphur + Sodium + Sulphur Thiosulphate Acid Chloride Dioxide Theory: In this experiment when the hydrochloric acid is added to the sodium thiosulphate, each of the liquids particles will collide with each other and bonds will be broken. When the concentration is higher the rate of reaction will be quicker, this is because when the concentration is higher there will be more particles and therefore bonds will be broken quicker as there will be more collisions. The rate of reaction is the speed at which, in this case the two liquids, hydrochloric acid and sodium thiosulphate react with each other. In this experiment we will measure the rate of reaction by placing a flask on top of a piece of paper with a black cross on it. Then we will add the two liquids to the flask and time the reaction until the black cross can no longer be seen. This happens because the reaction becomes murky and turns gradually opaque. There is a minimum amount of energy that particles need in order to collide with each other and react. ...read more.

Middle

* 2 x 50cm� measuring cylinder- 1 for measuring the thiosulphate and the other for measuring the amounts of water. Accurate enough to make results reliable. * Sodium Thiosulphate- To use in the experiment. * Hydrochloric acid- To use in the experiment. * Safety goggles- For safety reasons. * Stopwatch- To time the experiment. Accurate to 100th second. Time will be rounded up to nearest 10th of a second to eliminate human errors when timing. Fair Testing and Reliability To ensure that the test will be fair and reliable I will do the following: 1. Use the same cross underneath the beaker. 2. Use all the same apparatus. 3. Take all of my readings on the same day to avoid a possible temperature change if I took them over two periods that could affect the results. 4. Always use the same person to start and stop the stopwatch as different people may have different reaction times. 5. Take all the Thiosulphate and Hydrochloric acid from the same batch to avoid slightly different concentrations. Method: * Collect and set up the apparatus as stated above. * Place the conical flask on top of the piece of paper and then add 5cm� of hydrochloric acid to the flask. * Measure out, initially, 50 cm� of Sodium Thiosulphate and then add this to the hydrochloric acid. * Swirl the flask and then begin timing immediately. ...read more.

Conclusion

Naturally, the above means that the graphs plotting rate against concentration has positive correlation as the concentration is increased so does the rate of reaction. This is because when the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. When solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. Evaluation: In my opinion the experiment was a very big successful. I obtained a substantial quantity of very accurate results from which I was able to create informative graphs. I obtained a good amount of results. However if I was to repeat the experiment I would also test the effect of temperature on the reaction time. The range of concentrations was well chosen. This made my results more accurate and allowed me to make greater assumptions from my results. I felt my method was well thought-out and provided fair and reliable results. To make my results more accurate I could have measured the volumes of liquids more accurately. If I were to repeat the experiment I would have possibly found a more accurate way to measure out the solutions and to determine the concentrations. All my results followed the set pattern, but some were not as close to the line as others (slightly anomalous results). This could have been caused by human errors. Overall I was extremely pleased with my results. ...read more.

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