• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Compare the rate of hydrolysis of some halogeno-compounds.

Extracts from this document...

Introduction

Carmen Tse 7C 21 Chemistry Experiment No.19 Comparison of Rates of Hydrolysis of Halogeno-compounds Objective To compare the rate of hydrolysis of some halogeno-compounds. Introduction Halogeno-compounds are organic compounds composed of carbon, hydrogen and halogen. One of the characteristic reactions of haloalkanes is nucleophilic substitution reactions: Nu- + R-X --> R-Nu + X- In the above experiment, the nucleophile is H2O. OH- attacks the electropositive carbon centre and displaces a halide ion from the haloalkane. This kind of substitution is called hydrolysis. The halide ions substituted can be identified by silver nitrate solution. Ag+ (aq) + X- (aq) --> AgX (s) where X is the halide ions The overall equation is: OH- + R-X + Ag+ --> R-OH + AgX In this experiment, the rates of hydrolysis of halogeno-compounds are compared in 3 categories: 1. chloro-, bromo-, and iodoalkanes; 2. primary, secondary and tertiary haloalkanes; 3. haloalkane, halobenzene and (halomethyl)benzene Chemicals Ethanol about 20cm3 0.1M silver nitrate 10cm3 1-chlorobutane 5drops 1-bromobutane 15drops 1-iodobutane 5drops 2-bromobutane 5drops 2-bromo-2-methylpropane 5drops Bromobenzene 5drops Precaution Ethanol is volatile. It easily evaporates and the amount of ethanol in different test tubes would be less than 2cm3, especially when having water bath in partA. ...read more.

Middle

I- is said to be more polarizable. As the electrons are far away from the nucleus, the C-I bond is much weaker than C-Br and C-Cl bond and hence, I- is the best leaving group, followed by Br- and Cl- respectively. As a result, iodobutane is most reactive. Kinetic studies show that the nucleophilic substitution reactions proceed by two different reaction mechanisms. They are bimolecular nucleophilic substitution (Sn2) and unimolecular nucleophilic substitution. (Sn1) For Sn2, it just involved 1 step. There are no intermediates. The reaction proceeds through the formation of an unstable arrangement of atoms called the transition state. The rate of reaction depends on both concentration of haloalkane and hydroxide ion. Two species are involved in the rate determining step of the reaction. Rate = k [haloalkane] [OH-] For Sn1, it involved 2 steps and one intermediate is formed. The first step is the rate determining step and a carbocation is formed. The rate of reaction is independent of the concentration of hydroxide ion. Rate = k [haloalkane] In part B of the experiment, the experimental condition favours Sn1 reactions because the substrate bromobutane is rather bulky. Due to the effect of steric hindrance, bulky substituents on or near that carbon atom have a dramatic inhibiting effect. ...read more.

Conclusion

Ag+ (aq) + Cl- (aq) --> AgCl (s) Ag+ (aq) + Br- (aq) --> AgBr (s) Ag+ (aq) + I- (aq) --> AgI (s) Sources of error and Way of Improvement The water bath is set up by a Bunsen flame and the temperature is measured with thermometer. However, the temperatures always fluctuate. The temperature can influence the reaction rate greatly. A thermostatic bath can improve the accuracy of the experiment by keeping the temperature at 60C constantly. In the experiment, though it is difficult to keep the temperature at 60C constantly, the temperature in the three test tubes should keep the same as a fair test. A dropper is used when adding the halogeno-compound to the test tubes. However, dropper is not an accurate apparatus; the size of a drop can be very different. The amount of halogeno-compound added will directly affect the reaction rate thus the amount of precipitate. To improve, a pipette can replace the dropper. In using a pipette, more time will be need, it is quite impossible to compare the 3 test tubes at the same time. Some changes will be needed: 1. Use a timer to record the time for precipitates to appear. Or 2. Prepare the measured halogeno-compound before adding to ethanol and silver nitrate. ?? ?? ?? ?? 1 ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Patterns of Behaviour essays

  1. To compare the rates of hydrolysis of chloro-, bromo- and iodo- alkane.B. ...

    turn colorless AgBr White precipitate and turn colorless AgI Yellow precipitate and turn colorless With sunlight observation AgCl White precipitate and turned grey AgBr White precipitate and turned grey AgI Yellow precipitate and turned grey Conclusion A. The rate of hydrolysis are as follows: iodo-alkane > bromo-alkane > chloro-alkane B.

  2. Determination of the Cations and Anions

    which is a constant at a given temperature. Silver chloride is a relatively insoluble salt in water. It ionizes: Ag+ + Cl- - AgCl (s) The solubility product of AgCl, 1.8E-10 is also the equilibrium constant of this reaction which is calculated by multiplying the concentrations of silver and chloride ions in a saturated solution, for example [Ag+][Cl-].

  1. Identifying An Unknown Organic Compound

    This is because the blue litmus paper does not change to a red colour. A reaction with acidified potassium dichromate does not occur. This indicates that compound E may be a tertiary alcohol. If it were any other alcohol there would be a reaction and green chromium ion crystals would form.

  2. Find out how the rate of hydrolysis of an organic halogen compound depends on ...

    of the reaction. This is a constant and does not vary with temperature, R is the gas constant (8.3145 J mol-1 K-1), ln means log to the base e. A plot of ln k against 1/T follows the form 'y = mx' and should be a straight line.

  1. Free essay

    Close Your Eyes

    We walked out the front and down the street. Her house was quite far but we past the time by chatting about why I had moved and how I liked it so far. She was really nice and I was glad I'd met her cos otherwise I would have been walking home miserably, on my own.

  2. Rates of Reaction- Hydrolysis of Urea by Urease

    An enzyme is similarly affected by the pH. However this is more specifically related to the environment a particular enzyme is found in. Some enzymes prefer an acidic environment; others prefer a basic or neutral environment. Similarly, after the pH of the environment exceeds the optimum pH, the enzyme will also begin to denature.

  1. Halogenoalkanesshow how the rate of reaction of the halogenoalkanes changes in respect to the ...

    that can occur depending on the conditions used and the type of halogenoalkane. Primary, secondary and tertiary halogenoalkanes behave differently in this respect. These two reactions are substitution and elimination. In all cases, a mixture of both reactions will happen, some substitution and some elimination.

  2. Investigating the effect of enzyme concentration on the hydrolysis of starch with amylase.

    theory In this solution of starch and amylase there are only a few amylase molecules to collide with the starch substrate. This means is less chance of collision occurring and a less probability of the enzyme being 'locked' by the substrate starch 'key'.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work