Alcohols & Carboxylic Acids Flashcards

All 23 cards in this deck

What are the molecular formulae of methanol, ethanol, propan-1-ol and butan-1-ol?

$\mathrm{CH_3OH}$, $\mathrm{C_2H_5OH}$, $\mathrm{C_3H_7OH}$, $\mathrm{C_4H_9OH}$.
General formula: $\mathrm{C_nH_{2n+1}OH}$

What is the functional group in alcohols?

–OH, the hydroxyl group.

What type of compound is formed when an alcohol is dehydrated?
e.g. dehydrating propanol

An alkene (water is lost).
Propanol → propene + water

How do you draw the displayed structure of an alcohol?
e.g. ethanol, $\mathrm{C_2H_5OH}$

1. Draw the carbon chain joined by single bonds: C–C
2. Put an –O–H group on the end carbon: C–C–O–H
3. Add H atoms so each carbon has 4 bonds (no double bonds anywhere)

True or false? The functional group in alcohols is –OH, which is called the hydroxide group.

False. It is called the hydroxyl group; 'hydroxide' is not accepted.

Why do methanol, ethanol and propan-1-ol have similar chemical reactions?

They are in the same homologous series — their molecules all contain the same functional group, –OH.

What are the steps in the core practical to compare the temperature rise produced by burning different alcohols?
e.g. burning ethanol under $100\ \mathrm{cm^3}$ of water

1. Measure $100\ \mathrm{cm^3}$ of water into a metal calorimeter and record its starting temperature
2. Weigh the spirit burner containing ethanol, light it and heat the water, stirring
3. Put out the flame, record the final temperature and reweigh the burner; repeat with propanol, butanol and pentanol

Which measurements must be recorded in the alcohol combustion core practical?

Volume (or mass) of water, initial and final water temperature, and mass of the spirit burner before and after burning.

Apart from the volume of water, name two variables that must be kept the same when each alcohol is burned.

Distance from the flame to the container, and the length of the wick (also the same container and same starting temperature).

What is the main source of error in the alcohol combustion practical?

Heat lost to the surroundings and the apparatus instead of heating the water.
Incomplete combustion and evaporation of alcohol also reduce the result.

Give two improvements to the alcohol combustion practical.

Use a draught shield/screen and insulate the container (also use a copper calorimeter and a lid).

True or false? The energy released per gram calculated from this practical is usually higher than the accepted data-book value.

False. It is usually lower, because energy is lost to the surroundings and combustion may be incomplete.

What are the molecular formulae of methanoic, ethanoic, propanoic and butanoic acids?

$\mathrm{HCOOH}$, $\mathrm{CH_3COOH}$, $\mathrm{CH_3CH_2COOH}$, $\mathrm{CH_3CH_2CH_2COOH}$

What is the formula of the functional group in carboxylic acids?

–COOH (the carboxyl group).

What are the products when a carboxylic acid solution reacts with a metal carbonate?
e.g. ethanoic acid + sodium carbonate

A salt + water + carbon dioxide.
Ethanoic acid + sodium carbonate → sodium ethanoate + water + carbon dioxide

What is the word equation for the oxidation of ethanol?

ethanol + oxygen → ethanoic acid + water

True or false? When propanol is oxidised, propanoic acid is produced.

True. Each alcohol is oxidised to the carboxylic acid with the same number of carbon atoms (plus water).

What are the steps to make ethanol by fermentation?
e.g. from a glucose solution

1. Dissolve the carbohydrate (glucose) in warm water
2. Add yeast, keep at about 30 °C and exclude air
3. Leave to ferment: glucose → ethanol + carbon dioxide, then filter off the yeast

What is the word equation for the fermentation of glucose?

glucose → ethanol + carbon dioxide
$\mathrm{C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2}$

What is the role of yeast in fermentation?

It provides the enzymes (zymase) that catalyse the conversion of the carbohydrate into ethanol.

Why is fermentation carried out at about 30 °C rather than 80 °C?

At 80 °C the enzymes in the yeast are denatured, so they no longer work; at about 30 °C they are most effective.

What are the steps to obtain a more concentrated ethanol solution from a fermentation mixture?
e.g. distilling a dilute ethanol–water mixture

1. Heat the mixture in a flask with a fractionating column
2. Ethanol (boiling point 78 °C) evaporates first as it boils below water (100 °C)
3. Condense the vapour at about 78 °C and collect this ethanol-rich distillate

True or false? Fermentation on its own can produce pure ethanol.

False. It gives only a dilute solution (around 10–15% ethanol), so fractional distillation is needed to concentrate it.