1)Find the order of reaction with respect to hydrogen peroxide, iodide and acid using a ‘clock’ reaction. 2)To determine the rate equation, rate constant and the rate mechanism. 3)To determine the order of reaction with respect to the catalyst. 4)Look at the effect of a catalyst on the order of the reaction of hydrogen peroxide. 5)Find the activation enthalpy of the reaction with a catalyst. 6)Find the activation enthalpy of the reaction without a catalyst. There are many ways in which this experiment could be carried out.
Hydrogen peroxide reacts with iodide ions in acid solution to form iodine. H2O2(aq) + 2H +(aq) + 2I–(aq) > I2(aq) + 2H2O(l) By varying the concentration of the iodide ion, you can determine the order of this reaction with respect to the concentration of the iodide ions. The liberated iodine is reacted with thiosulphate (VI) ions, which have been added to the reaction mixture. I2 + 2S2O32- > 2I- + S4O62- When all of the thiosulphate ions have been used up, free iodine remains in solution and this is detected by the formation of a blue-black colour with starch indicator.
The appearance of the blue-black colour represents the same extent of reaction in each case, and so the initial rate is proportional to 1/time. Starter page 5: Kinetics of the reaction between magnesium and acids Aims: 1)To explore the reaction of magnesium with hydrochloric acid, sulphuric acid, or nitric acid. 2)Explore the effect of changing the concentration of the acid, the temperature or the addition of a catalyst on the rate of the reaction. 3)First find the order of reaction with respect to acids, after which you must find the rate equation, the rate constant and the possible mechanism.
4)Then find the activation enthalpy or explore the effect of added spectator ions. First of all, the rate equation must be determined using the inverted gas syringe method. Place excess acid (approximately 100cm3) in a beaker/conical flask and attach a bung to the flask with a syringe also attached to it via a flexible pipe medium. Place magnesium in the flask (starting the stopwatch as soon as this procedure has been performed) and then place the bung over the flask to seal it. Keep timing the reaction until 20cm3 of gas has been produced and then repeat this procedure at least twice more.
Then, the activation energy must be found. This can be achieved by placing the acid in a conical flask and then placing the conical flask in a larger container (a water-bath). A Bunsen burner flame can be placed under this to ensure that the temperature of the water in the container in which the conical flask has been placed is kept high. The inverted syringe should also be given access to the flask through a flexible pipe. The conical flask containing the acid solution should be left for five minutes to allow the acid to reach the temperature of the water bath and then, the magnesium should be added (and the stopwatch started).
The experiment should be timed until 20cm3 of gas is produced. Starter page 15: Hydrolysis of esters with acids Aims: 1)To hydrolyse methyl methanoate with an acid to form methanoic acid. 2)Find the order of the reaction, the rate constant and the activation enthalpy. 3)You can also find the effect of temperature/concentration/a catalyst on the equilibrium constant for the hydrolysis of the ester. To produce results for this experiment, you would need to hydrolyse the methyl methanoate with an acid to produce the carboxylic acid and an alcohol.
This can be monitored via titration or continuously using a conductivity meter. This is used to find the order of the reaction, the rate constant and the activation enthalpy. This experiment should then be repeated with methyl ethanoate and/or ethyl ethanoate. An acid exchange resin in a tea bag can also be used as a source of catalyst. The ethyl ethanoate should be hydrolysed with a dilute alkali. The ester should be heated under reflux with the dilute alkali (such as sodium hydroxide solution). The alcohol formed can be distilled off.
Then, to in order to obtain the acid rather than the salt, the reaction mixture should be titrated with an acid or using a conductivity probe. Starter page 17: Catalysis of the zinc/acid reaction Aims: 1)Determine the rate of reaction of the zinc and sulphuric acid. 2)Explore the catalytic effects of copper sulphate and other copper salts on the rate of the reaction. 3)Explore the effect of changing the concentration of copper sulphate on the rate of the reaction. 4)Investigate the possibility of copper alone catalysing the reaction. 5)Investigating whether silver nitrate or silver itself catalyses the reaction.
6)Note what happens to the colour of the copper sulphate solution as it is added to the reaction. Put a few pieces of granulated zinc into each of the three test-tubes. Try to have approximately the same amount in each test-tube. Add 5 cm3 of dilute sulphuric acid to test-tube 1. Note the rate of production of gas bubbles. Add a few copper turnings to test-tube 2. Make sure they are in contact with the zinc. Add 5 cm3 of dilute sulphuric acid and note the rate of production of gas bubbles. Add 5 cm3 of dilute sulphuric acid to test-tube 3.
Then add about 1 cm3 of the copper sulphate solution using a dropping pipette. Note the rate of production of gas bubbles. There may be enough hydrogen produced in test tube 3 to be tested using a lighted splint. You could also carry out the same experiment with the same conditions but different concentrations of the sulphuric acid each time to investigate what effect this has on the rate of reaction. This could be used to determine the order of reaction in relation to the sulphuric acid. You would use the inverted syringe method to carry out this investigation. Starter page 12:
The synthesis of aspirin in 3 steps Aims: 1)Produce Aspirin via an esterification reaction using ethanoic anhydride. 2)Synthesise Aspirin in a 3 step process, starting with 2-aminomethylbenzoate to produce 2 hydroxymethylbenzoate and then producing 2 hydroxybenzoic acid (salicylic acid) to finally produce Aspirin. 3)Re-crystallise the crude aspirin produced and purify it. 4)Use chemical tests, melting point, TLC and titrations to identify the various products. The aspirin is formed when you reflux ethanoic anhydride, phosphoric acid, and 2-hydroxybenzoic acid together for 15 minutes.
By quenching the reaction mixture with cold water, this forces the crude aspirin out of the solution. This crude aspirin can then be isolated by filtration. The crude aspirin obtained is purified by re-crystallisation from a minimum volume of hot aqueous ethanol and the pure aspirin crystals formed are then separated and dried by vacuum filtration. The purity of your aspirin sample can then be assessed by using both thin layer chromatography (TLC), with visualisation by U. V. , and also via determination of its melting point.