Effect of type of halide on the rate of hydrolysis of halogenoalkanes

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Effect of type of halide on the rate of hydrolysis of halogenoalkanes        

Debbie Warner

Introduction

halogenoalkanes
General formula- Rhal, (r is alkyl group, and Hal is a halogen atom)

In this experiment I will investigate the effects of the nature of the halogen atom (Hal) has on the reactivity of the halogenoalkane.

The rates of hydrolysis of different halogenoalkanes can be investigated by:

  • Alkaline hydrolysis with NaOH(aq)/H2O, reflux:

                                         R-X + OH→R-OH + X

  • Acidification with dilute nitric acid. This removes excess NaOH, which would otherwise form a precipitate with the silver nitrate in the next stage. Preventing detection of silver halides.
  • Addition of  AgNO3(aq) shows the presence of aqueous halide ions

Ag(aq) + X (aq)→AgX(s)

The intensity of any precipitate  indicates the extent and rate of hydrolysis.

Two factors that effect the rate of hydrolysis

Polarity predicts that the more polar C-Cl bond would attract water most easily and would give the faster reaction.

Bond enthalpy predicts the opposite that the C-I bond would be broken the most easily, therefore giving the fastest reaction.

For this reaction it is the bond empathy that is more important than polarity

So as the C-X bond weakens the rate of hydrolysis increases.

Hypothesis

From research I have done on the inter net and from preliminary experiments in the classroom, I predict that the 1-iodobutane with produce a precipitate first, next the 1-bromobutane, and finally the 1-chlorobutane. This is because C-I bond in 1-iodobutane would be broken most easily and that C-Cl bond would be broken least easily.

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Plan

Apparatus and chemicals needed

  • Test tubes
  • Test tube rack
  • Stop clock
  • 250cm beaker
  • Bunsen burner
  • Tripod
  • Heat proof mat
  • Gauze
  • Ethanol
  • Silver nitrate solutions, 0.01mol dm
  • Water
  • 1-chlorobutane
  • 1-bromobutane
  • 1-iodobutane

To make sure my results are accurate and reliable I will:

  • When measuring the liquid and aqueous chemicals in this experiment I will measure to the bottom of the meniscus to make sure my measurements are as accurate as possible.
  • Use a thermometer in both the water and inside the tubes themselves to make sure the hydrolysis takes place at the same temperature. ...

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