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Halogenoalkanesshow how the rate of reaction of the halogenoalkanes changes in respect to the C-X bond, where the C is the carbon and the X is the halogen (C-Cl, C-Br, C-I).

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The aim of this experiment is to show how the rate of reaction of the halogenoalkanes changes in respect to the C-X bond, where the C is the carbon and the X is the halogen (C?Cl, C?Br, C?I). Halogenoalkanes (also known as haloalkanes or alkyl halides) are compounds containing a halogen atom (fluorine, chlorine, bromine or iodine) joined to one or more carbon atoms in a chain. These are used in society as anaesthetics, plastics, solvents and as intermediates in reactions. The focus of these compounds is the carbon?halogen bond and all the nucleophilic substitution reactions of the halogenoalkanes involve breaking this bond. One of the main ways that halogenoalkanes react is by nucleophilic substitution. We can write a general equation for nucleophilic substitution using :N� to represent any negatively charged nucleophile: Their reactions are characterised by nucleophilic substitution of the halogen atom, owing to polarity of the carbon?halogen bond (C???X?-) in which the electron-deficient carbon (C??? is susceptible to attack by an electron-rich species, namely a nucleophile which can result in the displacement of the halide: X- (aq) ion. The nucleophile attaches itself to the C???atom while the halogen leaves as a halide ion (leaving group), taking the electrons of the C?X bond with it. ...read more.


C?Cl Cl = 3.0 0.177 346 C?Br Br = 2.8 0.194 290 C?I I = 2.5 0.214 228 As can be seen from the table above, the halogens decrease in electronegativity from Chlorine to Iodine, this forms a less polar molecule and therefore a smaller + charge on Carbon. However, the Carbon?Halogen bond length increases from Chlorine to Iodine and the bond becomes weaker and is consequently more easily broken which accounts for the lower enthalpy. This means polarity and bond enthalpy give contradicting predictions on the rates of reaction. My prediction for which bond will react most vigorously with the nucleophile at the greatest rate is C?I. For the reason that it has the lowest bond enthalpy meaning it can be broken with ease as it requires less energy. Consequently C?Br will not be as easy to break as C?I because of its higher bond enthalpy and will react slower. C?Cl will therefore be the hardest bond to break because it has the highest bond enthalpy of all the bonds being tested and will react slowest. I have decided to go with bond enthalpy as I feel that it is the more important property. I have dismissed polarity even though that would tell us that C?Cl would react quickest due to the large difference of sizes between the carbon and iodine resulting in a bigger C???charge thus allowing the nucleophile to attack the bond much easier. ...read more.


* The volume and concentration of ethanol * The volume and concentration of silver nitrate solution * The temperature of the water bath Contamination of solutions will also need to be prevented by washing out any cylinders and equipment before reusing them. Safety is exceptionally important and it is essential to follow safety procedures. It is important to wear eye protection when working with any chemicals that are irritant. Also long hair should be tied back. The halogenoalkanes are harmful when inhaled so every effort should be made not to breathe them in. Also as the chemicals used are highly flammable (1-iodobutane is flammable) it is important to take special care while working with and around them especially when near naked flame. Stoppers should be replaced straight away after use and kept well away from naked flames. Also to cuts and broken skin should be covered, and hands should be washed after handling the chemicals. If contact with skin does occur it should be washed with cold water immediately. The equipment needed to ensure safety would be goggles, lab coat, gloves and long hair tied back. Alcohol's are corrosive and can cause irritation to the skin. Refrences Essential AS Chemistry for OCR - Ted Lister, Janet Renshaw - P 115-118 http://www.chemguide.co.uk/mechanisms/nucsub/types.html#top Word Count: 1680 ?? ?? ?? ?? Taymaz Rad Chemistry Coursework AS - Assessed Practical - Rates of reaction of halogenoalkanes ...read more.

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