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    I am currently in the middle of my practicals for my salters chemistry investigation. The title of my investigation is investigating the substitution reactions of halogenoalkanes. I have completed the practical using the tertiary halogenoalkane 2-methyl-2-bromopropane. My aim is to calculate the order with respect to each reactant and therefore the rate equation for the reaction. I have decided to measure the initial rate of the reaction to do so. Firstly I react the halogenoalkane with potassium hydroxide using ethanol as a common solvent at room temperature. After 30s I quenched the reaction using Sulphuric acid and then did a back titration with Sodium Hydroxide. I have then tried to calculate the initial rate but have had many problems. I am hoping it is an error in my calculation that someone maybe able to help me with! The data is as follows:

    15 cm cubed of 0.02M Potassium Hydroxide solution in ethanol
    20cm cubed of ethanol
    0.1 cubed 0.1M 2-methyl-2-bromopropane
    Quenched with 50cm cubed of 0.01 molar Sulphuric Acid
    Indicator = 5 drops of phenol red
    Titre of 0.1M Sodium Hydroxide = 8.9cm cubed.

    And another set of data is:

    5 cm cubed of Potassium Hydroxide solution in ethanol
    0.6 cm cubed of 0.1 Molar 2-methyl-2-bromopropane
    20.4 cm cubed of ethanol
    Quenched with 20 cm cubed of 0.01M Sulphuric Acid
    Titre of 4 cm cubed using 0.1 Sodium Hydroxide
    Indicator = 5 drop of phenol red

    Any help with the calculation or advice for this experiment would be greatly appreciated!

    Did you vary the time at which you quenched and then titrated? In the first set of data I would assume that as quite a large volume of potassium hydroxide is used it's in excess and so it's conc. remains fairly constant so the rate would be k=[2-methyl-2-bromopropane]^x. Then I would plot a graph of time of quenching vs volume of sodium hydroxide needed to neutralise. Then I would vary the volume of 2-methyl-2-bromopropane (maybe double it for example - but then remember to keep the total volume the same so concentration of the halogenoalkane is effectively being changed) then again plot a graph of time of quenching vs. volume of sodium hydroxide needed to neutralise. I would then compare these two gradients and see how it corresponds to the change in volume of the halogenoalkane.

    Sorry if this is not of any use to you; I did this prac a long time ago! Good luck with it.
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Updated: November 17, 2008


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