alcohol

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ALCOHOL

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n Molecular Formula Structural Formula Isomer 1 2 3 4

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Based on the molecular formula of the alcohols below, draw their structural formulae. (a) 2-methylbutan-1-ol (b) 3-methylpentan-2-ol (c) 2,3-dimethylbutan-1-ol (d) 2,3,3-trimethylpentan-1-ol

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Preparation of ethanol in the laboratory Glucose Ethanol Pure Ethanol Fermentation by yeast Distillation Fermentation is a process of breaking down carbohytrates into ethanol (alcohol) Zymase enyzme in yeast acts on the carbohydrate and changes it into ethanol and releases carbon dioxide Distillation process is required to purify ethanol from the other products of fermentation

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Preparation of ethanol in the laboratory Activity Observation Solution in the conical flask Lime water Start of activity Clear solution with no smell clear End of activity Cloudy solution with an alcohol smell cloudy

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Distillation The clear liquid is distilled out at a temperature of 78 celcius. The product of distillation is colourless and smell of alcohol The boiling point of ethanol is lower than that of water, enabling it to be distilled out from the fermented products

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Pineapple juice or sugarcane juice can be used to replace the glucose solution, to obtain the same results. Porcelain pieces are used to break up the air bubbles in the liquid mixture. The Liebig condenser funtions to cool down and condense the vapour into liquid. Water enters the Liebig condenser from the bottom to ensure that the Liebig condenser is filled with water and no heat is trapped in the condenser. Drying agents such as calcium oxide, CaO, anhydrous copper(II)sulphate, or anhydrous calcium chloride can be added into ethanol to dry up the water that is still contained inside it.

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Physical properties of ethanol A colourless liquid at room temperature Sharp smell Low melting point and boiling point Soluble in water Very soluble in organic solvents such as ether Ethanol is less dense than water Q1: What can be observed when moist red or blue litmus paper is put into ethanol. No change. Because ethanol (alcohol) is neutral Q2: State the relationship between the boiling point of ethanol and its volatility. Low boiling point of ethanol (alcohol) causes it to be easily vapourised.

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Chemical Reaction Of Alcohols Combustion reaction Dehydrationreaction Oxidising reaction Esterification reaction Reaction with reactive metal + hot porcelain pieces + carboxylic acid + concentrate

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Complete Combustion of Ethanol ( in excess oxygen ) The combustion of alcohol releases a lot of heat and does not pollute the environment. Alcohol is a good fuel.

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Dehydration Dehydration reaction is a chemical reaction that involves the removal of a water molecule (elimination) from a compound. Ethanol can be changed into ethene Hydroxyl group is removed together with a hydrogen atom from an adjacent carbon atom There are two methods to carry out the dehydration of ethanol in the school laboratory: Ethanol vapour is passed over a heated catalyst such as unglazed porcelain chips, porous pot, pumice stone or aluminium oxide (alumina), silicon(IV)oxide Ethanol is heated under reflux at 170 celcius with excess concentrated sulphuric acid acts as a drying agent and catalyst.

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The porcelain pieces function as the catalyst and drying agent. The porcelain pieces need to be heated strongly first before heating the glass wool soaked in ethanol. This is because ethanol is very volatile. Ethene is collected using the water displacement method because ethene: Does not dissolve in water Is less dense than water

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3. When the gas is shaken with a little acidified potassium manganate(VII), the purple solution decolourises

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Alcohols can be easily oxidized to carboxylic acids. The alcohol group has gained an extra oxygen atom and is changed into a –COOH group. The ethanoic acid that is produced is a type of weak organic acid. Oxidising agent Acidified potassium dichromate(VI) Colour of the solution changes from orange to green Acidified potassium manganate(VII) Colour of the solution changes from purple to colourless

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