Unit 6 – Synthesising Organic Compounds Practical 2 Hydrolysis of Bromoethane to Ethanol Primary halogenoalkane can be hydrolysed to form alcohols. The reaction occurs when the halogenoalkane is refluxed with hydroxide ions (OH-) Halogenoalkanes are compounds containing a halogen atom (fluorine, chlorine, bromine or iodine) joined to one or more carbon atoms in a chain. Halogenoalkanes are insoluble in water so the solvent is usually ethanol/water mix. If water was used as the solvent, the halogenoalkane and the sodium hydroxide solution wouldn't mix and the reaction could only happen where the two layers met. Nucleophilic Substitution reaction. A nucleophile is an the electron rich species that will react with an electron poor species A substitution implies that one group replaces another. Reaction CH3CH2Br + Bromoethane + NaOH CH3CH2OH + NaBr Sodium Hyrdoxide Ethanol + Sodium Bromide Preparation Make sure that your lab coat is fully fastened at all times. Make sure you wear gloves and safety goggles at all times. This experiment should be carried out in the fumehood at all times. Part one- Hydrolysis of bromoethane to ethanol 1. Place 25mls of bromoethane into a round-bottomed Quickfit flask 2. Measure the bromoethane inside the fumehood. Add 25mls of 0.1M sodium hydroxide and a few pieces of anti-bump granules in to the round-bottomed Quickfit flask. 3. Measure the sodium hydroxide inside the fumehood. Swirl the flask gently to mix the reagents. Set up the Quickfit apparatus for refluxing as shown below. Instead of a Bunsen burner use the heating mantle. Turn on the water to run through the condenser. The water should come in at the bottom of the condenser and out at the top of the condenser. 4. Heat the solution under reflux to 70°C for 15 mins. Set the heating mantel to number 7. Rearrange the apparatus for distillation (as shown below – use the heating 5. mantle instead of the Bunsen burner). 6. Distil off the ethanol produced and collect in a clean, dry 100ml conical flask. Ethanol will be the first product to be distilled. Remember to record the temperature you start to collect liquid at. You can stop the distillation when the temperature begins to rise again. Part two – Test your product. 1. Record the temperature you started to distil a liquid at. 2. Record the volume of liquid distilled. 3. Take 3ml of your sample and place it into a clean boiling tube 4. Attach the boiling tube to the retort stand as shown overleaf. le Thermometer Retort Stand Boiling Tube Water Sample of Ethanol Apply Heat 5. Allow the ethanol to boil. 6. Record the temperature on the thermometer after the solution has begun to boil. This will be the temperature of the ethanol vapour Results 1. o Boiling point of your product = C Bromoethane + Sodium Hydroxide Ethanol + Hydrobromic acid 1 mole 1 mole 1 mole RMM of 1 mole of Bromoethane = 109 g 1 mole RMM of 1 mole of Ethanol = 46g Density of Bromoethane = 1.47 g/cm3, therefore in 1 cm3 of bromoethane = 1.47.g. Equation 1 – Determine the number of moles of bromoethane used in the reaction. Moles of bromoethane used in this reaction = Grams of bromoethane in 25cm3 RMM of 1 mole of bromoethane = moles In a 1:1 reaction the number of moles of bromoethane used = number of moles of ethanol produced. Equation 2 - Determine the mass of ethanol produced. Mass of ethanol = No. of moles of ethanol produced X RMM of 1 mole - of ethanol = g Equation 3 – Determine the percentage yield of product. Density of Ethanol = 0.76g/cm3 Volume of product = Density of 1cm3 of ethanol X mass (equation 2) = cm3 % Yield = Actual Yield Volume Volume of product = % Questions. 1. Is the % yield more or less than 100%? Explain your results. 2. Why is broken porcelain added to the solution before reflux? o 3. The actual boiling point of ethanol is 78.3 C, does this correspond to the temperature at which you distilled your product?? What would cause the liquid to be distilled at a different temperature?