This is an investigation into the reaction speeds of Sodium Thiosulphate [Na S O] under different conditions. We will be using a catalyst, which is Hydrochloric Acid [HCl]. Na S O + HCl ==> 2NaCl + SO + S + H O When the two chemicals are mixed the Sulphur slowly forms as a solid, but it does not precipitate out in the usual way. The time for a given amount of reaction can be found by checking the cloudiness of the mixture. The way in which we can find out the rate of reaction is by timing the reaction and finding out how long it takes for the liquid to become opaque under the conditions we set, then we divide the change by the time.

Then we will find out the effect of one factor on the reaction by only changing one input variable and keeping the rest constant. There are 5 variables for rate of reaction, Surface Area, Catalyst, Pressure, Concentration and Temperature. But only 3 of these are applicable to this experiment, Concentration, Catalyst and Temperature. Rate = A Chemical Change Time Taken A reaction happens when a successful collision occurs between 2 particles. For a successful collision to happen the bonds in each particle need to be broken so a new product can be made, and to do this it requires a certain amount of energy is needed.

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The energy in the collision is in the form kinetic energy when the 2 particles collide. When there is enough energy to create a reaction this is called Activation Energy, it is the least possible amount of energy needed to make the reaction occur. Variables:  Temperature – This will effect the reaction by a hot temperature giving the particles more energy to move faster, and therefore more kinetic energy so when to particles collide they will have more energy than normal to react so there will be a bigger chance of a successful reaction.

Concentration of Catalyst – The higher the concentration then more particles there in the liquid, which means there is more chance of to particles colliding, so the more collisions means there will be more chance of a successful collision occurring. Concentration of Reagent – If there is a higher concentration of Sodium Thiosulphate particles in the mixture, then there is a bigger chance of the 2 particles colliding and reacting. There fore the mixture will turn cloudier faster.

Surface Area – When the surface area is larger there are more collision taking place because there are more particles next to each other, there this will increase the chance of successful collisions.  Pressure – When the pressure is higher there are more collisions because the particles are forced together, there fore there are more chances of collisions, there fore the rate of reaction will increase with the pressure. The last 2 variables are not applicable to this experiment because the liquids mix so the surface area is always the same, and the pressure will make no difference on the liquids it is only for gases reacting.

Chosen Variable: Preliminary Results on Variation in Volume of HCl with 20cm Na S O and 20cm of Water. Volume of HCl in cm Time Taken The variable I am choosing is The Concentration of Sodium Thiosulphate. I have chosen to do this because in the preliminary results of the variation of the volume of HCl did not vary much and so it would not give good results for a graph, there is a bigger margin of error. To change the Sodium Thiosulphate I will dilute it at certain percentages with water to see what strength produces what RoR.

I will keep the other variable constant by keeping the temperature of both the Sodium Thiosulphate and Hydrochloric Acid, and the water; it should all be at room temperature. I will also keep the concentration of the HCl constant by not diluting it. Prediction: I predict that rate of reaction will increase as the concentration of the Na S O increases, there will be greater RoR; because there will be more particles of HCl to collide with the Na S O so more successful collisions will take place per cm/second. Therefore the liquid will become opaque faster. Predicted Graph: Rate of Reaction.

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