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Chemistry Major Practical On Factors Affecting the Rate of Reaction

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Introduction

CHEMISTRY MAJOR PRACTICAL ON FACTORS AFFECTING THE RATE OF REACTION AIM: To examine the ways in which changing the concentration of the reactant affects the rate of the reaction. The two chemicals used as reactants are Sodium Thiosulfate (Na2S2O3 (aq)) and Hydrochloric acid (HCL (aq)). The equation of the reaction is Na2S2O3 (aq) + HCL (aq) 2NaCl(aq) + H2O (l) + SO2 (g) +S(g) HYPOTHESIS/PREDICTION As reactions between solids reactants is much slower than liquid reactants we normally use liquids. According to the Collision theory three conditions must be satisfied before a reaction between molecules can occur. These are: a) the molecules must collide with one another b) the molecules must be made in a way that the right bonds can be broken and made c) there should be enough energy to make sure that the reaction can occur The first of the above three conditions affect this reaction. This is because as you lower the concentration you will lower the number of molecules in 1 litre of the solution (Because concentration or molarity of a substance is the number of moles of the substance present in 1 litre of the solution). KEY VARIABLES They key variables in this experiment are concentration, temperature, the size of the reactants and whether a catalyst is used or not. Because I've chosen to find the affect of changing concentration on the rate of reaction, I will have to keep everything else constant otherwise I won't be able to find out how much the concentration really affects the rate of reaction. ...read more.

Middle

8 Note the time in seconds and the concentration of the sodium thiosulphate. Experiment 2(involves water) This experiment is basically the same except for the first few steps where you have to add water to the sodium thiosulphate. The steps are: - 1 Take 35 ml of sodium thiosulphate in the 50-ml measuring cylinder and add 5 ml of water to it, to decrease its concentration. 2 Calculate and note the new concentration, and repeat the steps 2 - 8 in experiment 1 All the values have been noted in the table below OBSERVATIONS In all the experiments the reactants were the same , hence the observations were also the same. As soon as the Na2S2O3 was added to the HCl in the conical flask , the reaction started, it developed a white-yellowish cloudy mixture, which became more and more dense as time increased . It reached a point where the black cross , was completely diminished .This was because more and more sulphur was precipitating as time went by . DATA ANALYSIS We know that m = CV , where c is concentration , m is the no. of moles , v is the volume . Hence we can work out the no. of moles of Na2S2O3 in each experiment and can get the concentration by simply dividing the no. of moles by the volume of the Na2S2O3 + water solution . ...read more.

Conclusion

Errors could also arrive due some uncertainties , which are : Firstly for time , as we can only measure temperature to the nearest minisecond there could be an uncertainty of + or - 0.005 seconds . Hence the actual value for time should be measured value + or - 0.005 seconds . Secondly and similarly as we can only measure temperature to the closest degree Celsius there could be an uncertainty of + or - 0.5 degrees Celsius. Therefore the actual value should be measured value + or - 0.5 degrees Celsius . Safety precautions: In order to work in the chemistry lab we have to consider certain safety precautions to avoid health hazards . In this particular experiment we should use the following safety precautions: 1 All the used chemicals should be disposed off carefully, as they could be poisonous, and all the apparatus should be washed and dried with care . 2 Safety goggles and gloves should be used if working with a burner or strong chemical. 3 Other safety utensils like holder, stand, glass rod, etc. should be used wherever appropriate. 4 All the glass utensils should be handled with care in order to avoid breakage and cuts. There are many other safety precautions used in various other experiments but we are only concerned with this particular practical, therefore the above stated precautions should be enough. Modifications In order to improve on this practical I can use some modifications which are: 1 Doing the practical in one day so that there isn't any change in room temperature. 2 ...read more.

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