Reactions occur when Hydrochloric acid particles collide with the Magnesium. They all work by increasing the number of Magnesium collisions. There are a number of factors that change the speed of a reaction: Temperature Concentration of Hydrochloric acid Surface area Addition of a catalyst To make a choice for this experiment we have to choose which is the most feesable in the circumstances. Temperature: Temperature will affect the rate of reaction because an increase will speed up the movement of the Particles so that they collide more frequently.
However, it is not a good option in the circumstances because the required amount of variations is 5, and using an icebox, room temperature and heating (we would not be able to keep different levels of heat constant) gives us only three variations. In addition, the reaction between a metal and an acid is exothermic, so the temperature of the experiment would not be the same half way through as at the beginning. Surface area: Increasing the surface area of the magnesium would increase its amount of exposure to the Hydrochloric acid at one time, therefore increasing the rate of reaction.
However, it is quite difficult to measure the surface area accurately enough to say that one specimen is exactly double (i. e. ) the surface area of another Catalyst: There is no substance that can speed up the rate of reaction whilst staying separate from Magnesium and Hydrochloric acid. Concentration: You can accurately measure the concentration of an acid in Molars (M). If you increase the concentration of the Hydrochloric acid, then the rate of reaction is increased, proportionally. I am going to use a total of six concentrations:
Molars I will use for each a solution of water (neutral), and Hydrochloric acid (2 M). This is the table to show how the different strengths were achieved: Concentration achieved (M) Amount of water (ml)(%of sol) Amount of HCl (ml)(%of sol) 0. 75M, I used an 80ml test tube to make the soloution 5/8 Hydrochloric Acid and 3/8 Water, then poured 50ml of it into a test tube, so the results above are the precise (although not the ones we used) amounts needed to achieve these concentrations Graph Prediction:
Rate Y=X Concentration Because an increase in concentration is proportional to an increase in rate, I predict that the graph will show a linear result. Eventually there will be an optimum rate, where the line becomes horizontal, although not in the duration of this experiment. Measure of rate: Mg(s) + 2HCl(aq) MgCl +H 2 2.
Magnesium + Hydrochloric = Magnesium Chloride+ Hydrogen Acid To decide what the method of measuring the rate will be, we have to look at the products of the experiments: Magnesium Chloride: You can measure what speed the Magnesium ‘disappears’ in the flask as it turns into Magnesium Chloride. This would mean weighing a piece of Magnesium and then leaving it for a specific amount of time and finding the difference. However, this would leave you with only one result and you could not make it accurate by studying its progress. Hydrogen: You could measure the amount of Hydrogen produced in two ways:
1. You could measure the declining weight of the flask, which would be very difficult and very inaccurate because hydrogen weighs so little. 2. You can show the volume of Hydrogen produced, visibly using a gas syringe, which would be quite accurate. I am going to choose to use the gas syringe, as the results will be clearer and more accurate. Preliminary work: I decided to do some preliminary work to determine what balance of acid and metal will give the most workable result (i. e is not to fast, does not go off the scale). Amount of acid (M) Amount of Magnesium (cm).