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Planning Coursework - Investigation of rate of hydrolysis of halogenoalkanes

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Introduction

Investigation of rate of hydrolysis of halogenoalkanes By Fiona Li L6LB Introduction In this experiment, it is intended to investigate the relationship between different types of halogenoalkanes and their rate of hydrolysis. Three different types of halogenoalkanes will be used in this experiment. They are 1-chlorobutane, 1-bromobutane and 1-iodobutane. Outline of the experiment The experiment will be done by using different types of halogenoalkanes, with a suitable volume of ethanol added in each test tube. Placing the test tubes into the water bath and stand for few minutes to ensure the temperature of the solution mixture remains constant for a fair test. Silver nitrate is added into the mixture and shakes afterwards. The mixture will then undergo hydrolysis following this equation: RH (l) + H2O (l) --> ROH (l) + H+ + X- N.B The water molecules come from the aqueous silver nitrate solution At the same time, the stopwatch will be press started to record the time needed for the formation of silver halides (which is a precipitate formed by the silver ions in silver nitrate solution with the X-, which is a halide ion produced by the hydrolysis of halogenoalkanes). The time needed for the completion of the precipitate formation will be recorded and the data obtained will be analyzed to give an appropriate conclusion. Observation and measurements going to be seen and recorded When silver ions react with halide ions, a coloured precipitate will form, which is insoluble in water. ...read more.

Middle

As halogenoalkanes and silver nitrate cannot be dissolved in water, forming layers of solution, ethanol is used as a common solvent such that both solute can be dissolved for reaction to happen. However, if the amount of ethanol used in the experiment is not the same, for example, less ethanol is used for a particular test tube some of the halogenoalkanes may not be dissolved. Apparatus The apparatus used in this experiment will be as follows: Test tubes x 5 Test tube rack x 1 Graduate pipette x 5 Large beaker x 1 Thermometer x 1 Stopwatch x 1 N.B graduate pipette is used as it has measuring interval such that the volume of the solution can be accurately measured. The graduated pipette is having a volume of 2cm3 and with 0.2cm3 interval such that to give an accurate measurement of the volume of solution used. Safety precautions As the halogenoalkanes is a highly volatile substances which is flammable and is toxic when in contact with skin, the following safety precautions have to be taken to prevent serious damage: 1) To ensure there is not Bunsen burner placing near the halogenoalkanes as they are highly flammable, if they are spilled onto the naked flame, it may cause fire. It is also needed to be aware that when discarding the halogenoalkanes solution, it should be done in the fume cupboard to carry away any harmful and toxic gas. ...read more.

Conclusion

3) In a separate test tube, place in 10cm3 of silver nitrate solution. 4) In the beaker, add in suitable volume of water which able to cover the mixture in the test tube. Place in all the test tube, wait for 10 minutes, this is to allow the temperature of the solution to be equilibrium (i.e the mixture in the 4 test tubes are having the same temperature). Measure the temperature in the water bath using a thermometer. Place a black colour paper at the back of the test tubes. 5) Add in 2cm3 of silver nitrate, shake using inversion method to ensure the silver ions are even disturbed over the solution. At the same, start to the stopwatch. 6) Stop the stopwatch once the solution changes from colourless to cloudiness and the black colour of the paper cannot be seen. This indicates the end point of the reaction. Record the time needed for the complete hydrolysis process. 7) The experiment may have to be repeated for 2 more times to eliminate any potential errors and to obtain a average result for accurate analysis. Analysis of results After obtaining sufficient results from the experiment, an average time taken for the hydrolysis process for each halogenoalkanes will be calculated. A table will be drawn to show the results for comparison. The shorter the time needed for the precipitate formation, the faster the rate of hydrolysis that particular halogenoalkane has. The table can also be used to show the rate of hydrolysis for each type of halogenoalken by using the equation of rate = 1 / time. ...read more.

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