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Investigate, analyse and evaluate the effect on the rate of reaction of varying the concentration of hydrochloric acid in the reaction with magnesium.

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Introduction

Sam Daniels Chemistry Coursework AN INVESTIGATION INTO THE REACTION BETWEEN HYDROCHLORIC ACID AND MAGNESIUM * Aim My aim is to plan, investigate, analyse and evaluate the effect on the rate of reaction of varying the concentration of hydrochloric acid in the reaction with magnesium. The chemical equation of the reaction I am investigating is: Mg (s) + 2HCl (aq) --> MgCl2 (aq) + H2 (G) * Rate of Reaction Rate of Reaction = Gas Produced Time taken To measure the rate of reaction I can use three ways: Precipitation - this is when the reaction's product is a precipitate which clouds the solution. Change in mass - a reaction which produces a gas will lose mass and this can be shown by carrying out the reaction on a balance. Volume of gas given off - A gas cylinder gas be used to collect the gas given off. Rate of reaction depends on four separate things: Temperature, concentration (or pressure for gases), size of particles (or surface area for liquids) and the presence of a catalyst. Rate of reaction is a change in mass or volume or concentration per unit of time. An increased rate could be the product of any of these factors: an increase in temperature, an increase in concentration, an increase in surface area or the introduction of a catalyst. * Variables The variables available to investigate are: Mass of Magnesium Used Temperature of surroundings Time of reaction taking place Pressure (atmospheric) Volume of HCl used Volume of H2 produced Concentration of HCl Shaking/Stirring Surface Area of Magnesium Turnings or Ribbon Magnesium A dependent variable is a factor which changes due to another variable changing. This variable is an independent variable and it is the variable that is changing. For my dependent variable I will use Volume of H2 produced and collected, and also I will measure the temperature of the reaction at the start and at the end of my reaction and for my independent variable I will change the concentration of hydrochloric acid used in terms of mol/dm�. ...read more.

Middle

* Prediction I predict that the more concentrated the hydrochloric acid is, the faster the rate of reaction will be, and the faster the hydrogen will be given off. I also think that the amount of hydrogen gas given off will be proportional to the concentration of the hydrochloric acid. These predictions can be justified in terms of the collision theory: for two molecules to react, they have to collide. The rate of a chemical reaction depends on how often the molecules collide (the frequency of collision) and with how much energy they collide (the energy of collision). Sufficient energy is important so there is enough energy to break the bonds in the reacting molecules. Energy will then be released when new bonds and new molecules form. Molecules also have to collide so that the reactive parts of them come together (with the correct orientation). More collisions increase the rate of reaction and all methods of increasing the rate of reaction can be explained in terms of the increase of the number collisions between the particles of the reagents. Temperature, concentration (or pressure), size of solids particles (or surface area) or the presence of a catalyst increases the number of collisions. I also predict that the graph of volume of gas produced against concentration and rate of reaction against concentration will be a straight line because the gas produced is proportional to the concentration. * Results Experiment 1 Temp in Lab (�c) Concentration of HCl (mol/dm�) Mass of Mg (g) Volume of HCl (cm�) Time (s) Volume of H2 collected (cm�) Before Expt. After Expt. 19 20 0.6 0.10 25.0 60 3.8 20 21 0.8 0.10 25.0 60 5.2 21 22 1 0.10 25.0 60 7.5 19 20 1.2 0.10 25.0 60 9.6 20 21 1.4 0.10 25.0 60 8.4 Experiment 2 Temp in Lab (�c) Concentration of HCl (mol/dm�) Mass of Mg (g) ...read more.

Conclusion

These include using a measuring gas syringe and using another person as well as some one to start the timer to replace the bung quicker so no gas is lost. Using a gas syringe will increase the accuracy of the results because it is graduated more than a measuring cylinder and the graduations can be seen clearer than on a measuring cylinder because there is no meniscus of the water to affect the level. The experiment was quite reliable due to the method I used and the apparatus I used. My experiment was repeatable, this means that if I repeated my experiment over and over again, the results would turn out roughly the same. I would like them to always be within 5% of each other and at most there should be a 10% difference between the results. I could perform further experiments to support my investigation. This would give me an idea about what other factors affect the rate of reaction and in what way. I could extend my experiment by for example: reading the amount of gas produced at intervals during the reaction is occurring and hence see how the rate of reaction changes from the start to the finish of the reaction. I could use a different metal to see if the reactivity of the metal affects the reaction, I could use a different acid, a smaller or larger mass, a smaller or larger volume of reactants to increase or decrease the rate of reaction. I could also add the element of temperature into the investigation: I could submerge the apparatus and the reactants in a water bath set at a certain temperature, leave them for a while to become the desired temperature and then perform the experiment. This method would take longer to prepare but I believe it would be worth it. * Sources Used CGP GCSE Double Science Chemistry - The Revision Guide Higher Level Notes from classes throughout the Chemistry Nelson Science by John Holman Sam Daniels - Set 2 07/05/2007 GCSE Chemistry Coursework 2003/4 2 ...read more.

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