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An investigation into the effect of concentration on the rate of chemicl reaction between sodium thiosulphate and hydrochloric acid.

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Aim The aim of this investigation is to find out and observe how concentration affects the rate of reaction. I am going to investigate the changes caused to the solution of hydrochloric acid and sodium thiosulphate when the concentration is changed. Background information The rate or speed of a chemical reaction is a measure of how fast the reaction takes place. The rate of reaction gives the measure of how the reaction is proceeding. How is the rate of reaction found? To find the rate of reaction, it is necessary to measure either: * The amount of a reactant used per unit of time (or) * The amount of product produced per unit of time. If one products of the reaction is a gas, it can be collected and its volume measured as it is evolved by means of a gas syringe. The rate of evolution of gas can then be used as a measure of the reaction. Example- during the experiment between Magnesium and dilute hydrochloric acid, the products are magnesium chloride and hydrogen. The gas can be collected and its volume measured at intervals using the apparatus below. Collision theory of reaction Reaction takes when particles collide. Most collision does not produce a reaction because colliding particles need a minimum energy to react when they collide. E.g.: 2H2 (g) + O2 (g) ==> 2H2O When H2 and O2 molecule collide, they must have energy to break the H-H and the O=O bonds in H2 and O2 before they can react to form water. The collisions must be enough of energy to overcome the energy barrier; called the activation energy. The more frequently particles collide, the faster is the reaction. How rate of reaction is measured 1) Measure how long it takes for a reaction to be completed. ...read more.


Safety The things that I will need to do to keep my experiment safe for myself and other students around me are as follows: * I will wear goggles to protect my eyes * I will wear a lab coat to protect my clothes and skin * I will tuck my stool out of the way, so no one can trip over it. * I will stand up whilst doing my experiment, so that just in case if something spills, I will be able to get away fast * I will not leave the apparatus at the side of the table, so it cannot get knocked over. Plan The reaction between sodium thiosulphate and hydrochloric acid is well known and has been used to study the rates of reaction. When these chemical are combined they form a sulphur precipitate in the form of a suspension which turns the transparent opaque. Hydrochloric + Sodium thiosulphate sodium + water + sulphur + sulphur acid chloride dioxide HCl (aq) + Na2S2O3 (aq) NaCl (aq) + SO2 (g) + S (s) + H2O (l) A simple set of experiments may be performed to determine the effect of concentration on the rate of reaction. By using a conical flask with a cross marked piece of paper positioned underneath it, then add 25cm3 of sodium thiosulphate and then add 25 cm3 of 0.3 mole of hydrochloric acid then start the stop watch and time the duration of the cross to disappear. The pattern will disappear after a specific quantity of sulphur has formed The faster the reaction, the shorter the length of time during which the cross is invisible. The experiment is carried out several times with solution of hydrochloric acid to different concentrations. ...read more.


If I could do this experiment again, this should hopefully give me an extra set of results that prove my results are reliable and my prediction is right. This all depends if I have more time to do so. I believe that the experiment was designed well but there were a few problems. Although the initial rate of reaction ( which is what I am concerned with in this investigation) seemed to fit a trend, the rate of reaction curves of all concentration on the graphs crossed only 0.6 M concentration acid didn't crossed. The reason is that these anomalities could occurred, is that I could not measured the acid or sodium thiosulphate out correctly from the measuring cylinder. Also, I could have started the stop watch slightly after or before I actually should. In the second graph the only concentration that I could make straight line is 1.0 M concentration of hydrochloric acid. However, it is a strong positive correlation which mean that as I increase the concentration the rate of reaction increases. The result on the first graph which is a curve graph there was only one problem which on 0.6 M, it is not going with the curve line. And on the second graph there is two point which are o.7 M and 1.0 M. I conducted all experiment for each concentration at the same time to save time. An error in my graphs (plotting, drawing curves) could have also affected the calculated rates of reaction. The information that I collected could be adequate to support my conclusion fully. However, I could collect more evidence by doing more repeats and maybe doing more different concentration of hydrochloric acid. Additional work, which could be carried out, is to repeat the experiment using, a wider range of concentrations. ?? ?? ?? ?? Mona Ibrahim Chemistry Coursework 1 ...read more.

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