The effect of temperature on the reaction between Sodium Thiosulphate (Na2S2O3) and Hydrochloric Acid (HCl) :: GCSE Chemistry Coursework Investigation

Investigating the effect of temperature on the reaction between Sodium Thiosulphate (Na2S2O3) and Hydrochloric Acid (HCl) Planning and Prediction Apparatus List Conical Flask 3 measuring cylinders Sodium Thiosulphate (Na2S2O3) Hydrochloric Acid (HCl) Thermometer Stop watch When sodium thiosulphate reacts with hydrochloric acid, the solution becomes opaque. I will investigate how the rate of this reaction is affected when the experiment is carried out at different temperatures. The reaction that occurs produces sulphur dioxide, water and sodium chloride. GRAPH The rate of chemical reactions can be affected by a number of things:  · changes in surface area  · changes in concentration of the reactants  · changes in temperature  · added substances called catalysts  · and changes in pressure if the reactants are gases. In most chemical reactions the rate changes with time, normally slowing down. Prediction I will be investigating the effect that temperature has on the reaction between sodium thiosulphate and hydrochloric acid. I predict that the higher the temperature, the faster the reaction will occur. This should happen because when heat is applied to a solution the particles in the compounds move faster and therefore come into contact with the other substance more rapidly. More importantly, the collisions are more energetic. An increase in collisions provides more energy than there is in the activation energy, so the reaction is faster. Preliminary Investigation In order to discover what ratio of HCl to Na2S2O3 I needed to conduct a preliminary experiment, changing the concentration of the various reactants. I will need a time of two or three minutes at 20 °C, my lowest temperature, because I predict that the reaction will speed up as the temperature is higher, and I do not want the reaction to happen in just three or four seconds once I get to 60 °C as it will be difficult to measure the time accurately. GRAPH It was discovered after the preliminary experiments that there had been some contamination so the results were inaccurate. With a larger amount of Na2S2O3 than HCl the experiment should have happened slower not faster. After further trials I discovered that: Water 40mls Na2S2O3 10mls HCl 5mls gave me an adequate starting time of approximately 3:00 - 3:30 minutes at 20 °C. As a result of my preliminary investigation I will add water to dilute the Na2S2O3, as otherwise it is too concentrated and the reaction