Organic Compounds - Their Structure And Reactions
Visão Geral
Leave a glass of wine open on a warm windowsill for a fortnight and it turns into something you would put on a salad rather than something you would drink. Nothing was added to it. No one heated it. A colony of bacteria drifting in the air landed on the surface, went to work on the ethanol, and handed back a different substance with a sharp smell and a sour taste. That substance is ethanoic acid, and the whole of this lesson lives in the small structural difference between the molecule the wine started with and the molecule it finished with.
Two families of compound are on the table here, and each one is defined by a single cluster of atoms bolted onto the end of a carbon chain. Change the cluster and you change everything the compound will do: one family dissolves to give a neutral solution and burns cleanly enough to run a car, while the other fizzes with carbonates, turns indicator red and gives vinegar its bite. You will learn to spot each family from a name or a formula, to write balanced equations for what they do, to follow the single reaction that converts the first family into the second, and to explain why an acid can be genuinely acidic and still be called weak.
Objetivos
- Alcohols contain the functional group -OH. Methanol, ethanol and propanol are the first three members of a homologous series of alcohols. Alcohols can be represented in the following forms: CH3CH2OH or H H | | H C C O H | | H H Students should be able to recognise alcohols from their names or formulae, but do not need to know the names of individual alcohols other than methanol, ethanol and propanol.
- Methanol, ethanol and propanol: dissolve in water to form a neutral solution; react with sodium to produce hydrogen; burn in air; are used as fuels and solvents, and ethanol is the main alcohol in alcoholic drinks.
- Ethanol can be oxidised to ethanoic acid, (a carboxylic acid) either by chemical oxidising agents or by microbial action. Ethanoic acid is the main acid in vinegar.
- Ethanoic acid is a member of the homologous series of carboxylic acids, which have the functional group -COOH. The structures of carboxylic acids can be represented in the following forms: CH3COOH or H | H C C O | | H O H Students should be able to recognise carboxylic acids from their names or formulae, but do not need to know the names of individual carboxylic acids other than methanoic acid, ethanoic acid and propanoic acid.
- Carboxylic acids: dissolve in water to produce acidic solutions; react with carbonates to produce carbon dioxide; react with alcohols in the presence of an acid catalyst to produce esters; do not ionise completely when dissolved in water and so are weak acids; aqueous solutions of weak acids have a higher pH value than aqueous solutions of strong acids with the same concentration. Students are expected to write balanced chemical equations for the reactions of carboxylic acids.
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- Which functional group is present in all alcohols? A. -COOH B. -OH C. -COO- D. -CH3 Answer: B
- Ethanol is oxidised by microbial action to form which compound? A. ethene B. ethane C. ethanoic acid D. propanol Answer: C
- Which gas is produced when ethanoic acid reacts with sodium carbonate? A. hydrogen B. oxygen C. chlorine D. carbon dioxide Answer: D
- Which gas is produced when a small piece of sodium is added to ethanol? A. carbon dioxide B. oxygen C. hydrogen D. chlorine Answer: C
- A solution of hydrochloric acid and a solution of ethanoic acid have the same concentration. Which statement is correct? A. The ethanoic acid has a higher pH because it is only partially ionised. B. The ethanoic acid has a lower pH because it is only partially ionised. C. The two solutions have the same pH because their concentrations are equal. D. The ethanoic acid has a pH above 7 because it is a weak acid. Answer: A
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