Alcohols and haloalkanes

Question 1

What are haloalkanes used for in daily life

Answer 1

Haloalkanes are used to make solvents, polymers ,refrigerants and pesticides

Question 2

Draw the word equation of bromoethane

Answer 2

C2H5OH + NaBr + H2SO4 —> C2H5Br + H2O + NaHSO4

ethanol + sodium bromide + sulfuric acid —> Bromoethane + water + sodium hydrogen sulfate

Question 3

What happens during the formation of bromoethane

Answer 3

Ethanol is heated under a reflux with a mixture of sodium bromide and sulfuric acid The sulfuric acid has a concentration of around 50%.

In the first stage, the sodium bromide and sulfuric acid react together to form hydrogen bromide and sodium hydrogen sulfate

In the second stage the hydrogen bromide reacts with the ethanol to form bromoethane and water.

Bromoethane , water and sodium hydrogen sulfate is formed as products. This is through the substitution of the alcohol with the bromine atom. (Substitution reaction)

The product haloalkanes is then separated

Question 4

Draw the word equation of the first reaction to form Bromoethane

Question 5

Draw the word equation of the second reaction to form Bromoethane

Question 6

Why are haloalkanes distilled

Answer 6

Due to the volatile properties of haloalkanes

Question 7

What is a hydration reaction

Answer 7

The electrophillic addition of water to alkenes to make alcohols

Question 8

Key points in hydration reactions

Answer 8

In hydration water is in the form of steam

Phosphoric acid is used as a catalyst

The temperature is 300c and the pressure is 60 atmospheres

Question 9

Explain the reaction mechanism of a hydration reaction

Answer 9

Phosphoric acid has three hydrogen atoms each bonded to oxygen which is a strongly
electronegative element. Therefore, it is a polar molecule. (Oxygen = - / hydrogen = +)

Stage 1)

The pair of electron in the pi bond of the alkene is attracted to the positive charge of the hydrogen atoms in the phosphoric acid. (Positive hydrogen acts as an electrophile)

The pair of electrons in the pi bond form a covalent bond to the positive hydrogen atom. At the same time, the covalent bond between the hydrogen and oxygen breaks.
The pair of electrons completely move to the oxygen atom. ( covalent bond breaks with both electron going to the same atom- heterolytic fission)

A carbocation intermediate is formed with a positively charged carbon atom and a dihydrogen phosphate ion with a negatively charged oxygen atom with a negatively charge oxygen atom. (Phosphoric acid is a catalyst therefore needs to be regenerated at a later stage)

Stage 2)

The carbocation intermediate reacts with a molecule of water (steam). The oxygen atom in a water molecule has two lone pairs of electrons. One lone pair forms a covalent bond between the oxygen and the positive carbonate atom on the carbocation intermediate
We then have an intermediate molecule containing a positive charged oxygen atom.
(The oxygen is positive as the lone pair of electron have formed a covalent bond)

Stage 3)

Dihydrogen phosphate ion forms a covalent bond to a hydrogen in the intermediate molecule. At the same time, the covalent bond in the intermediate now breaks by heterolytic fission and the pair of electrons in the bond now move completely onto the oxygen.

A product is made and phosphoric acid is regenerated.

Question 10

Explain what happens when we hydrate asymmetric alkenes

Answer 10

We apply Markownikoff’s rule to determine which carbon atom will bond to the hydrogen atom of the water and which will bond to the OH group.

The hydrogen is more likely to bond to the carbon atom which is already bonded to the greater number of hydrogen atoms.

Question 11

Write a word equation for the hydrogenation of ethene

Answer 11

Ethene + hydrogen —(nickel catalyst)—-> ethane

Question 12

What is the alcohol function group known as

Answer 12

A hydroxyl group

Question 13

What is the alcohol function group known as

Answer 13

A hydroxyl group

Question 14

How do you name an organic compound with one alcohol functional group

Answer 14

We put the name of the organic compound first then add a number to show which carbon the OH group is attached to. (We want the number to be as small as possible). Then we substitute the end of the name with oil

Question 15

How do you name an organic compound with two hydroxyl groups

Answer 15

If an alcohol molecule contains two hydroxyl groups, then we call it a diol

We number the hydroxyl so it produces the lowest possible number

In the case of diols we use the whole name of the parent alkane

The same method is used for three hydroxyl functional groups although it is called a triol

Question 16

How do you name an organic compound with an alcohol functional group and another function; group

Answer 16

We treat the alcohol as the parent molecule therefore must have a suffix of ol

However, certain other functional groups have naming priority over alcohols such as aldehydes, ketones and carboxylic acids. Therefore, the molecule is name after the higher priority functional group and the alcohol group is shown by the prefix hydroxy

Question 17

Explain primary alcohols

Answer 17

The carbon atom bonded to the hydroxyl group is bonded to one other carbon atom

Question 18

Explain secondary alcohols

Answer 18

The carbon atom bonded to the hydroxyl group is bonded to two other carbon atom

Question 19

Explain tertiary alcohols

Answer 19

The carbon atom bonded to the hydroxyl group is bonded to three other carbon atom

Question 20

What are the three categories of alcohols

Answer 20

Primary , secondary and tertiary alcohols

Question 21

What are the properties of alcohols compared to alkanes with the same number of carbon atoms

Answer 21

Alcohols have a higher boiling point than the alkane with the same number of carbon atoms.

As we increase in the number of carbon atoms, the difference in boiling points between the alcohol and the corresponding alkane reduces.

Question 22

Explain why alcohols have a greater boiling point than alkane with the same number of carbon atoms

Answer 22

Alkanes are non-polar molecules. Therefore, have a lack of polarity. Thus only London forces are acting between the alkane molecules. London forces are weak and do not take much energy to break. Therefore, alkanes have low boiling points.

In contrast, alcohols are polar molecules. This is due to the alcohol functional group. Oxygen atoms are much more electronegative compared to hydrogen atoms. Thus oxygen has a negative charge whereas hydrogen is positively charged.

This means that alcohol molecules can form both London forces and hydrogen bonds to each other ( hydrogen bond are relatively stong and require a relatively large amount of energy to break) . Therefore, since alcohol contains both London forces and hydrogen bonds they have higher boiling paint than alkenes with the same number of carbon atoms.

Question 23

What is volatility

Answer 23

How readily a molecule turns to a gas

Question 24

What does alcohols having a higher boiling points than alkanes achieve.

Answer 24

Because alcohols have higher boiling point than alkanes. Alcohols are less volatile than alkanes with the same number of carbon atoms.

Question 25

Explain why as we increase in the number of carbon atoms, the difference in boiling points between the alcohol and the corresponding alkane reduces.

Answer 25

Alkanes only have London forces whereas in alcohols, we find both London forces and hydrogen bonds. In an alcohol with a short carbon chain the major intermolecular force is hydrogen bonding due to the alcohol functional group whereas, London forces are less significant. Therefore, short-chain alcohols have a much greater boiling point than the corresponding alkane. However, alcohols with long carbon chains the contribution of London forces increases. And the relative importance of hydrogen bonding is reduced. Therefore, the boiling point of long chain alcohols are only slightly greater than corresponding alkanes.

Question 26

Explain how hydrogen bonding explains alcohols solubility

Answer 26

Alcohols are highly soluble in water. As the alcohol functional group can form hydrogen bonds with water molecules. As we increase the length of the carbon chain, alcohols become less soluble in water. This is because the non-polar carbon chain cannot form hydrogen bonds. So as we increase the length of the carbon chain a greater part of the molecule is unable to hydrogen bond to water molecules. This makes long chain alcohols less water-soluble than short chain alcohols. In contrast to alcohols, alkanes molecules are insoluble in water. Because, they are non-polar molecules, alkanes cannot form hydrogen bonds with water molecules.

Question 27

What is created when a primary alcohol is oxidised

Answer 27

An aldehyde And a molecule of water

Question 28

How is oxidation carried out

Answer 28

Oxidation is carried out through the use of a chemical called a oxidising agent (potassium dichromate with dilute sulfuric aid {acidified potassium dichromate})

Question 29

What is the colour of potassium dichromate

Answer 29

It has an orange colour

Question 30

what is the formula of potassium dichromate

Answer 30

k2Cr2O7 / H+ However scientist often use a capital O in square brackets. This symbol shows that one molecule of oxidising agent is taking part in the reaction

Question 31

What happens during the reaction of a primary alcohol and an oxidising agent.

Answer 31

During reaction, the oxidising agent is reduced from the dichromate (VI) ion which is orange to the chromium (III) ion which is green

Question 32

What is a problem during the reaction of a primary alcohol and an oxidising agent

Answer 32

Aldehydes are extremely easy to oxidise further . Therefore, if we want to make an aldehyde then we must remove it from the reaction as soon as it forms. If not then it could oxidise Aldehydes are easily oxidised and when aldehydes are oxidised they make a carboxylic acid.

Question 33

Explain a solution to the problem of the reaction of a primary alcohol and an oxidising agent

Answer 33

Aldehydes molecule have low boiling points as they cannot form hydrogen bonds. This means that as it forms, we can easily remove it through distillation. By gently heating the alcohol and oxidising agent, we produce the aldehyde. The aldehydes evaporates and passes into the condenser where it condense back into a liquid and is removed. We favour the production of aldehyde by making sure the starting alcohol is in excess and the oxidised agent is limiting.

Question 34

Explain oxidisation of a primary alcohol to carboxylic acid

Answer 34

When reacting a primary alcohol to a carboxylic acid. This reason requires two molecules of oxidising agent. When we carry out this reaction we want to make certain that all of the aldehyde produced is then oxidised to the carboxylic acid. To do this when need to use an excess of oxidising agent. we need two molecule of oxidising agent to oxidise a primary alcohol to a carboxylic acid. We also can use concentrated sulfuric acid then dilute sulfuric acid We heat the reaction under reflux. When we heat a reaction under reflux any volatile products are condensed and return to the reaction mix. By heating under reflux,we can heat the chemicals until the reaction completes and we make our carboxylic acid. At the end, our reaction will contain a mixture of chemicals. We will have our product which is the carboxylic acid plus any unreacted alcohol and aldehyde. Plus unreacted oxidising agent. Carboxylic acids have higher boiling points than aldehydes. This is because carboxylic acids can form hydrogen bonds. So at the end of the reaction, we can use distillation to separate out our carboxylic acid from the reaction mix.

Question 35

Describe the oxidation of secondary alcohol to tertiary alcohol

Answer 35

We can use acidified potassium dichromate to oxidise a secondary alcohol When a seconadary alcohol is oxidised, we make a ketone and water. The solution turns from orange to green if acidified pottasium dichromate is used as an oxidising agent.

Question 36

Key ideas of oxidation of secondary alcohols

Answer 36

Ketones cannot be oxidised any further

Question 37

Explain why Ketones cannot be oxidised any further

Answer 37

During oxidation, we remove a hydrogen from the carbon atom bonded to the alcohol group. As you can see, once we form the aldehyde the carbon atom bonded to the oxygen still has another hydrogen to remove. This means that aldehydes can be oxidised further to a carboxylic acid. However, in a ketone the carbon atom bonded to the oxygen is not bonded to any more hydrogen atoms. Therefore, we cannot oxidise ketones any further. When we oxidise a secondary alcohol. We heat the reactants under reflux. By heating under reflux, we can ensure that as much of the ketone forms as possible. At the end of the reaction we will have a mixture of chemicals. We will have our products, which are the ketone and water. We’ll also have unreacted alcohol and oxidising agent. At the end of the reaction, we use distillation to separate our ketone from the mixture. ketones cannot form hydrogen bonds. This means that ketones are volatile chemicals with relatively low boiling points.

Question 38

Explain why tertiary alcohols cannot oxidise

Answer 38

In tertiary alcohols, the carbon atom bonded to the alcohol group is not bonded to any hydrogen atoms. This means that tertiary alcohols are not easily oxidised under normal laboratory conditions. If we heat a tertiary alcohol in the presence of acidified potassium dichromate then no reaction happens and the oxidising agent remains orange in colour

Question 39

How can alcohols be dehydrated

Answer 39

An alcohol can be converted to an alkene through heating under reflux in the presence of either concentrated sulfuric aid or concentrated phosphoric (V) acid. The concentrated acid acts as a catalyst for this reaction. An alkene and a water molecule will be created. At the end of he reaction, we can purify the alkene by distillation. In this reaction, we are producing a water molecule from the parent alcohol. Scientist say that the alcohol underwent dehydration to form the alkene. (Elimination reaction)

Question 40

What happens during an elimination reaction

Answer 40

In an elimination reaction, a small molecule is removed from a larger parent molecule. In the case of dehydration of alcohols, the small molecule is water

Question 41

Key points of dehydration of alcohols

Answer 41

Structural isomers of alkenes can be created Additionally, the isomers may consist of two different geometrical isomers

Question 42

what type of reaction is the combustion of alcohols

Answer 42

it is an exothermic reaction, releasing energy

Question 43

what is the balanced equation for the complete combustion of ethanol

Answer 43

C2H5OH (l) + 3O2 (g) —-> 2CO2 (g) + 3H2O (l) Ethanol + oxygen —> carbon dioxide + water

Question 44

what are the products in the complete combustion of an alcohol

Answer 44

Always carbon dioxide and water

Question 45

Key ideas when balancing equation

Answer 45

We can only use large numbers We can never change any of the small numbers in any of the molecule involved The large number in front of a molecule multiples all of the atoms in that molecule