alcohols

Question 1

Alcohols are ?

Answer 1

Alcohols are a family of organic (carbon-based) compounds. Ethanol is an alcohol that can be produced by fermentation or by direct synthesis from crude oil products.

Question 2

Alcohols all contain the ??? group and this is generally responsible for their chemical properties and reactions.

Answer 2

Alcohols all contain the –OH group and this is generally responsible for their chemical properties and reactions.

Question 3

They are named after their ?

Answer 3

They are named after their ‘parent’ alkanes, for example: methanol (alcohol) and methane (‘parent’ alkane); ethanol (alcohol) and ethane (‘parent’ alkane

Question 4

What is the molecular formua of Methanol and Ethanol?

Answer 4

Methanol

CH3OH

Ethanol

C2H5OH

Question 5

What are the Uses of methanol and ethanol

Answer 5

Methanol can be used as a chemical ‘feedstock’ (starting material for other chemical reactions), in anti-freeze and in the production of biodiesel.

Ethanol can be used as a solvent and as a fuel.

Question 6

What are the Physical properties of alcohols?

Answer 6

Physical properties of alcohols

Short-chain alcohols like methanol and ethanol have a low boiling point (ie lower than water) because they have weak intermolecular forces which are easily overcome. Longer chain alcohols have higher boiling points

Question 7

Alcohols have higher or lower boiling points than their corresponding alkane ? Why?

Answer 7

Alcohols have higher boiling points than their corresponding alkane (eg ethanol has a higher boiling point than ethane) because the –OH group has the effect of strengthening the intermolecular forces

Question 8

Short chain alcohols are ……………..in water because ?

Answer 8

Short chain alcohols are very soluble in water because of the effect of the –OH group that is strongly attracted to water molecules.

Question 9

Longer chain alcohols are less soluble in water because ?

Answer 9

of the effect of the –OH group that is strongly attracted to water molecules.

Longer chain alcohols are less soluble because they behave more like an alkane and tend to float on top of the water.

Question 10

Why are Alcohols a source of fuel?

Answer 10

Alcohols are good fuels because of the presence of the hydrocarbon chain. They burn in a good air supply to produce carbon dioxide and water.

Question 11

Give an example of how alcohols burn in a good air supply to produce carbon dioxide and water.

Answer 11

For example:ethanol + oxygen → carbon dioxide + water

C2H5OH + 3O2 → 2CO2 + 3H2O

Question 12

Ethanol can be made by ……………… In fermentation, what happens?

Answer 12

Ethanol can be made by fermentation. In fermentation, sugars are used by yeast as a source of energy for anaerobic respiration.

Question 13

What are the products of fermentation?

Answer 13

Ethanol and carbon dioxide are the products:

glucose → ethanol + carbon dioxide

Question 14

Why are optimum conditiosn needed for fermentation?

Answer 14

Because this reaction is catalysed (sped up) by enzymes in the yeast, there are optimum conditions that are needed:

Question 15

What is the correct temperature for fermentation? What happens if it is lower or higher?

Answer 15

A temperature of approximately 37°C - any lower and the reaction is slow, but any higher and the enzymes are denatured - which changes the shape of the active site on the enzyme.

Question 16

What is the optimum pH -? What happens if it is significantly high or low pHs ?

Answer 16

An optimum pH - significantly high or low pHs will also prevent the active site on the enzyme from working properly.

Question 17

If the concentration of ethanol exceeds a certain level, it will start to ?

Answer 17

If the concentration of ethanol exceeds a certain level, it will start to kill the yeast. This means that there is a limit to the concentration of ethanol that can be achieved through fermentation.

However, the concentration of the ethanol can be further increased by distillation, which is how spirits like whiskey and brandy are made

Question 18

However, the concentration of the ethanol can be further increased by what method? What is made this way?

Answer 18

However, the concentration of the ethanol can be further increased by distillation, which is how spirits like whiskey and brandy are made

Question 19

Ethanol can also be made using biotechnology. How?

Answer 19

Genetically-modified E. coli bacteria can be used to convert waste biomass from a range of sources into useful ethanol. The biomass might have come from plant matter such as maize stalks or wood waste.

The optimum conditions for the bacterial enzymes are similar to those required by the enzymes in the yeast used in traditional fermentation

Question 20

Ethanol can be made using what as a raw material?

Answer 20

Ethanol can be made using crude oil as a raw material.

Question 21

What are the stages in the synthesis of ethanol?

Answer 21

1.
Crude oil is processed by fractional distillation.

2.
Alkanes (such as ethane) are ‘cracked’ to produce alkenes - including ethene (C2H4).

3.
Ethene is reacted with steam at high temperatures and in the presence of a phosphoric acid catalyst.

4.
Any unreacted ethene and steam are recycled back into the process so that they are not wasted.

Question 22

Why is fermentation a good process for people in the developing world ? What are the limits?

Answer 22

Fermentation can be done with very simple technology, so it allows people in the developing world to produce ethanol from crops. However, there is a limit to the concentration of the ethanol that can be produced, and it is expensive to use this process to make large quantities.

Question 23

Is Fermentation likely to be carbon neutral? Why?

Answer 23

Fermentation is more likely to be carbon neutral. This is because the amount of carbon dioxide that is produced when the ethanol is burned is the same as the amount that was absorbed by photosynthesis when the plants that have been fermented were growing

Question 24

In addition to their reactions with oxygen when they are burned, alcohols react with sodium to produce What? Give an example

Answer 24

ethanol + sodium → sodium ethoxide + hydrogen

2C2H5OH + Na → 2C2H5O-Na+ + H2

Because alkanes do not react with sodium it is unlikely to be the carbon chain in the alcohol that is causing this reaction to take place.

On the other hand, water reacts vigorously with sodium, suggesting that it is the –OH group in the alcohol which is causing the reaction between an alcohol and sodium.
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