Reactions of alkenes and alcohols

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Apuntes de la lección

Alkene Structure and Formulae

Alkenes are hydrocarbons that contain a carbon-carbon double bond (C=C).
The C=C double bond is the functional group of alkenes and is responsible for their characteristic reactions.
The general formula of the alkene homologous series is CnH2n.
The first four alkenes are ethene (C2H4), propene (C3H6), butene (C4H8) and pentene (C5H10).
Alkenes are unsaturated compounds because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms.
The position of the double bond can be shown by a number, e.g. but-1-ene has the C=C starting at carbon 1.
Alkenes are more reactive than alkanes because the C=C bond can open up to form single bonds, allowing other atoms to attach.

Combustion of Alkenes

Alkenes undergo complete and incomplete combustion in air.
Because alkenes have a higher carbon to hydrogen ratio, they tend to undergo incomplete combustion, producing a smoky flame.
Complete combustion occurs with excess oxygen and produces carbon dioxide and water.
Example: butene + oxygen → carbon dioxide + water.
Incomplete combustion occurs with insufficient oxygen and can produce carbon monoxide and/or carbon (soot) along with water.
Example: butene + oxygen → carbon monoxide + water, or butene + oxygen → carbon + water.
Smoky yellow flames indicate a higher carbon to hydrogen ratio in the molecule.

Addition Reactions of Alkenes

Alkenes mainly undergo addition reactions, in which atoms of a simple molecule add across the C=C double bond.
The double bond opens up to form a single bond, allowing two more atoms to bond, one on each carbon.
A saturated compound is formed when an alkene undergoes an addition reaction.
Hydrogenation: alkenes react with hydrogen at 150 °C using a nickel catalyst to form an alkane.
Hydrogenation is used to make margarine from vegetable oils by partially hydrogenating polyunsaturated oils to increase Mr and turn them into solid fats.
Hydration: alkenes react with steam at around 330 °C and 60–70 atm using a concentrated phosphoric acid catalyst to form an alcohol.
Halogenation: alkenes react readily with halogens at room temperature, with halogen atoms adding across the C=C bond.
The bromine water test: bromine water is an orange-yellow solution; when shaken with an alkene, the colour is decolourised (turns colourless) because an addition reaction occurs.

Alcohols: Structure and Uses

All alcohols contain the hydroxyl (-OH) functional group.
The first four alcohols are methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH) and butanol (C4H9OH).
Alcohols are named using the alkane name with the final 'e' replaced by 'ol'.
Alcohols are colourless liquids that dissolve in water to form neutral solutions.
The first four alcohols are commonly used as fuels.
Methanol and ethanol are used as solvents because they dissolve many substances that water cannot, such as fats and oils.
Ethanol is the alcohol found in alcoholic drinks and is also used as a fuel for vehicles.

Reactions of Alcohols

Alcohols undergo combustion to form carbon dioxide and water; e.g. ethanol + oxygen → carbon dioxide + water.
Alcohols react with sodium metal to produce hydrogen gas and a metal salt (e.g. sodium + methanol → sodium methoxide + hydrogen).
Alcohols can be oxidised to produce carboxylic acids.
When ethanol is heated with acidified potassium dichromate, it oxidises to ethanoic acid; the solution turns from orange to green.
The oxidation of ethanol in wine left open to air produces ethanoic acid, giving a vinegary taste.

Production of Ethanol by Fermentation

Ethanol can be produced by fermentation: sugar or starch is dissolved in water and yeast is added.
Fermentation takes place between 15 and 35 °C in the absence of oxygen for a few days.
Yeast contains enzymes that break down sugar to alcohol; if too cold the reaction is slow, if too hot the enzymes are denatured.
The yeast respires anaerobically: glucose → carbon dioxide + ethanol.
Yeast is killed once the alcohol concentration reaches about 15%, so the vessel is emptied and the process restarted — this makes fermentation a batch process.
Fermentation produces a dilute ethanol solution; fractional distillation is used to separate ethanol (boiling point 78 °C) from water (100 °C).

Carboxylic Acids: Structure and Reactions

Carboxylic acids contain the -COOH functional group.
The first four carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.
They are named using the alkane name with the final 'e' replaced by 'oic acid'.
Carboxylic acids are soluble in water, forming weakly acidic solutions.
They react with carbonates to produce a metal salt, water and carbon dioxide gas.
They react with alcohols in the presence of an acid catalyst (concentrated sulfuric acid) to form esters — this is esterification.
Esters have the functional group R-COO-R; they are sweet-smelling oily liquids used in flavourings and perfumes, and are volatile.
Example: ethanoic acid + ethanol → ethyl ethanoate + water.

Carboxylic Acids as Weak Acids (HT only)

Carboxylic acids show typical acid reactions but are weak acids.
They dissolve in water but only partially ionise, producing solutions with pH between 3 and 7.
They form an equilibrium with their ions, but most molecules remain undissociated.
Ethanoic acid is about 95% undissociated — only about 5 out of 100 molecules ionise.
Because they are weak, their reactions are often slow or barely noticeable at room temperature.

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Preguntas de práctica

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1.Which statement correctly describes alkenes?
Easy
- AAlkenes are saturated hydrocarbons
- BAlkenes are unsaturated hydrocarbons
- CAlkenes contain hydrogen, carbon and oxygen atoms
- DAlkenes contain only single carbon-carbon bonds
2.What is the correct general formula of an alkene?
Easy
- ACnH2n+2
- BCnH2n
- CCnH2n+1OH
- DCnH2n+1COOH
3.What is the correct general formula of an alcohol?
Easy
- ACnH2n+2
- BCnH2n
- CCnH2n+1OH
- DCnH2n+1COOH
4.The functional group in alcohols is the hydroxyl group, -OH.
Easy
True or false?
5.Bromine water is decolourised when shaken with an alkane.
Easy
True or false?
6.Which of the following is the molecular formula of ethene?
Easy
- AC2H6
- BC2H4
- CC3H6
- DCH4
7.Which of the following is the molecular formula of ethanol?
Easy
- ACH3OH
- BC2H5OH
- CC3H7OH
- DC2H4
8.What type of reaction takes place between ethene and bromine?
Medium
- ASubstitution
- BAddition
- CCombustion
- DNeutralisation

Más preguntas

9.Which of the following statements about alkenes are correct? (select all that apply)
Medium
- AAlkenes contain a C=C double bond
- BAlkenes are unsaturated compounds
- CAlkenes undergo addition reactions
- DAlkenes are saturated hydrocarbons
- EAlkenes have the general formula CnH2n+2
10.Which of the following are products of the complete combustion of an alcohol? (select all that apply)
Medium
- ACarbon dioxide
- BWater
- CCarbon monoxide
- DSoot (carbon)
- EHydrogen
11.Match each alcohol to its correct molecular formula.
Medium
- Methanol
- Ethanol
- Propanol
- Butanol
- CH3OH
- C2H5OH
- C3H7OH
- C4H9OH
12.Butene reacts with steam to produce butanol. What type of reaction takes place between butene and steam?
Easy
- AAddition
- BDehydration
- CNeutralisation
- DSubstitution
13.Here are five statements about the reactions of alkenes. Select the two statements that are correct. (select all that apply)
Medium
- AAlkenes react with bromine water to form a colourless solution
- BAlkenes react with bromine water in a substitution reaction
- CAlkenes react with oxygen to form carbon dioxide and water
- DAlkenes react with bromine water to form an unsaturated compound
- EAlkenes react with oxygen to form carbon dioxide and hydrogen
14.Both alkenes and alkanes undergo combustion reactions. What type of reaction is combustion?
Medium
- AThermal decomposition
- BOxidation
- CAddition
- DNeutralisation
15.Alkenes can be formed from the cracking of long chained hydrocarbons. What type of reaction is cracking?
Medium
- AThermal decomposition
- BCombustion
- CNeutralisation
- DOxidation
16.A sample of each of three hydrocarbons, X, Y and Z, was shaken with orange bromine water. X and Y both turned the mixture colourless, while Z left the mixture orange. Which statement about the structures of X, Y and Z is correct?
Medium
- AX and Y are unsaturated and Z is saturated
- BX and Y are saturated and Z is unsaturated
- CX, Y and Z are all unsaturated
- DX, Y and Z are all saturated
17.Match each reaction of an alkene to the product it forms.
Medium
- Ethene + hydrogen (with a nickel catalyst)
- Ethene + steam (with a phosphoric acid catalyst)
- Ethene + bromine water
- Ethene + excess oxygen (complete combustion)
- Ethane
- Ethanol
- 1,2-dibromoethane
- Carbon dioxide and water
18.Which of the following are conditions used to produce ethanol industrially by the hydration of ethene? (select all that apply)
Medium
- AA temperature of around 330 °C
- BA pressure of 60–70 atm
- CConcentrated phosphoric acid catalyst
- DA temperature of 15–35 °C
- EYeast enzymes
19.During fermentation, yeast uses glucose to produce ethanol and carbon dioxide.
Easy
True or false?
20.In the fermentation of a sugar solution using yeast, which condition is required?
Medium
- AA temperature between 15 and 35 °C with no oxygen present
- BA temperature between 15 and 35 °C with plenty of oxygen present
- CA temperature above 100 °C with no oxygen present
- DA temperature of exactly 78 °C with plenty of oxygen present
21.A student heats a mixture of ethanol and water to 78 °C during fractional distillation. Why is this temperature chosen?
Medium
- AIt is the boiling point of ethanol, so the ethanol evaporates while the water remains
- BIt is the boiling point of water, so the water evaporates while the ethanol remains
- CIt is the temperature at which ethanol freezes and can be removed
- DIt is the temperature at which yeast enzymes are denatured
22.Place the stages of producing and purifying ethanol by fermentation into the correct order, starting with the first step.
Medium
- Dissolve sugar or starch in water and add yeast
- Leave the mixture to ferment between 15 and 35 °C without oxygen for a few days
- Heat the dilute ethanol solution to 78 °C so the ethanol evaporates
- Condense the ethanol vapour to form liquid ethanol
23.Which of the following statements about the reactions of alcohols are correct? (select all that apply)
Medium
- AAlcohols burn in air to form carbon dioxide and water
- BAlcohols react with sodium to produce hydrogen gas
- CAlcohols react with sodium to produce carbon dioxide gas
- DAlcohols are oxidised by acidified potassium dichromate to form carboxylic acids
- EAlcohols are oxidised by acidified potassium dichromate to form alkenes
24.When ethanol is heated with acidified potassium dichromate solution, what colour change is seen?
Medium
- AOrange to green
- BGreen to orange
- CColourless to orange
- DOrange to colourless
25.Ethanoic acid is the carboxylic acid formed when ethanol is oxidised.
Easy
True or false?
26.Which of the following is the functional group of a carboxylic acid?
Medium
- A-COOH
- B-OH
- CC=C
- D-COO-
27.Ethanoic acid reacts with ethanol in the presence of concentrated sulfuric acid. What type of compound is formed?
Medium
- AAn ester
- BAn alkene
- CAn alcohol
- DA carboxylic acid
28.Which of the following statements about carboxylic acids are correct? (select all that apply)
Medium
- AThey dissolve in water to form weakly acidic solutions
- BThey react with carbonates to produce a metal salt, water and carbon dioxide
- CThey react with alcohols to form esters
- DThey fully ionise in water like hydrochloric acid
- EThey form strongly alkaline solutions in water
29.Carboxylic acids dissolve in water to form weakly acidic solutions with pH values between 3 and 7. Why are they weak acids?
Hard
- AThey only partially ionise in water, so most molecules remain undissociated
- BThey do not dissolve in water at all
- CThey fully ionise in water, releasing many hydrogen ions
- DThey release hydroxide ions into the water
30.Which alcohol released the most energy per gram of alcohol burned?
Medium
- APentanol (37.6 kJ/g)
- BButanol (36.3 kJ/g)
- CPropanol (33.5 kJ/g)
- DEthanol (29.8 kJ/g)
31.Place the four alcohols in order of increasing energy released per gram, starting with the lowest.
Medium
- Ethanol
- Propanol
- Butanol
- Pentanol
32.A student burns equal masses of four alcohols and records the temperature rise of 100 cm³ of water each time. The results are: ethanol 28 °C, propanol 32 °C, butanol 35 °C, pentanol 37 °C. Which alcohol is the best fuel per gram?
Medium
- AEthanol
- BPropanol
- CButanol
- DPentanol
33.A sample of an unknown hydrocarbon is shaken with orange bromine water. The mixture turns colourless. Which statements are correct? (select all that apply)
Hard
- AThe hydrocarbon is unsaturated.
- BThe hydrocarbon contains a carbon-carbon double bond.
- CThe hydrocarbon is an alkane.
- DAn addition reaction has taken place.
- EThe hydrocarbon has the general formula CnH2n+2.
34.A student heats ethanol with acidified potassium dichromate solution. The mixture changes from orange to green. The student wants to obtain ethanoic acid from the reaction mixture. Which method is most suitable?
Hard
- AFilter the mixture to remove the green colour.
- BFractionally distil the mixture to separate the ethanoic acid.
- CAdd bromine water to decolourise the mixture.
- DEvaporate the mixture to dryness in an open dish.
35.During the fermentation of a sugar solution, oxygen must be excluded because fermentation is an anaerobic process.
Easy
True or false?
36.Ethene is hydrated industrially to make ethanol. The reaction chamber contains unreacted ethene, ethanol and water. The mixture is passed into a condenser. Which substance leaves the condenser as a gas?
Medium
- AEthene
- BEthanol
- CWater
- DEthanoic acid
37.A student adds a few drops of universal indicator to separate solutions of ethanoic acid and hydrochloric acid of the same concentration. Which statements explain the difference in pH observed? (select all that apply)
Hard
- AEthanoic acid only partially ionises in water.
- BHydrochloric acid ionises completely in water.
- CEthanoic acid is a strong acid.
- DEthanoic acid molecules are mostly undissociated.
- EHydrochloric acid is a weak acid.
38.A student adds a piece of sodium metal to a test tube of ethanol. Which observation is correct?
Medium
- AA gas is produced that pops with a lighted splint.
- BA white precipitate forms immediately.
- CThe solution turns from orange to green.
- DThe solution turns from colourless to orange.
39.In the core practical investigating the heat of combustion of alcohols, 100 cm³ of water is placed in a copper can. Why is a copper can used rather than a glass beaker?
Medium
- ACopper is a good conductor of heat, so energy from the flame is transferred efficiently to the water
- BCopper is a catalyst for the combustion of alcohols
- CCopper has a low specific heat capacity, so it absorbs very little energy from the flame
- DCopper prevents the alcohol vapour from escaping from the burner
40.A student burns methanol, ethanol, propanol and butanol in turn, using each alcohol to raise the temperature of 100 cm³ of water by 25 °C. Which change to the method would most improve the reliability of the comparison of the four alcohols?
Hard
- ARepeat each alcohol burn and calculate a mean mass of alcohol used
- BUse 200 cm³ of water for each alcohol instead of 100 cm³
- CUse a glass beaker instead of a copper can
- DHeat the water until it boils rather than stopping at a 25 °C rise
41.Complete the sentences about the bromine water test.
Easy
Bromine water is an ____ solution. When it is shaken with an alkene, the solution becomes ____.
42.Calculate the relative molecular mass (Mr) of ethanol, C2H5OH. (relative atomic masses: H = 1, C = 12, O = 16)
Medium
43.Butene reacts with steam to produce butanol: C4H8 + H2O → C4H9OH. Calculate the maximum mass of butanol, in kg, that can be produced when 1.4 kg of butene reacts with excess steam. (relative molecular mass of butene, C4H8 = 56; relative molecular mass of butanol, C4H9OH = 74)
Medium
44.A student burns propan-1-ol in a spirit burner to heat 100 g of water. The temperature of the water rises by 20 °C. Using Q = m × c × ΔT with c = 4.18 J g⁻¹ °C⁻¹, calculate the energy transferred to the water in joules.
Medium
45.Complete the word equation for the complete combustion of an alcohol.
Medium
ethanol + ____ → carbon dioxide + ____
46.Butene undergoes complete combustion: C4H8 + 6O2 → 4CO2 + 4H2O. How many oxygen molecules, O2, are needed to completely burn one molecule of butene?
Medium
47.In a calorimetry experiment, 100 g of water is heated by burning an alcohol. The temperature of the water rises by 25 °C. Calculate the energy transferred to the water in joules. Use Q = m × c × ΔT, where c = 4.18 J g⁻¹ °C⁻¹. Give your answer to the nearest whole number.
Medium
48.A spirit burner containing ethanol loses 0.56 g of mass while heating 100 cm³ of water and raising its temperature by 40 °C. Calculate the energy released per gram of ethanol burned. Use Q = m × c × ΔT with c = 4.18 J g⁻¹ °C⁻¹, and give your answer in kJ/g to 1 decimal place.
Medium
49.Calculate the relative molecular mass (Mr) of propanoic acid, CH3CH2COOH. (relative atomic masses: H = 1, C = 12, O = 16)
Medium
50.A fermentation reaction produces 2.3 g of ethanol. Calculate the number of moles of ethanol produced. (Mr of ethanol = 46) Give your answer to 3 decimal places.
Hard
51.Ethene reacts with steam to form ethanol: C2H4 + H2O → C2H5OH. Calculate the maximum mass of ethanol, in kg, that can be produced from 2.8 kg of ethene reacting with excess steam. (relative molecular masses: C2H4 = 28, C2H5OH = 46)
Hard
52.A sample of ethanol is burned completely: C2H5OH + 3O2 → 2CO2 + 3H2O. If 0.5 mol of ethanol is burned, what mass of carbon dioxide is produced? (Mr of CO2 = 44) Give your answer in grams.
Hard
53.Describe the test to distinguish between an alkane and an alkene, and state the result for each.
Medium
54.Describe how you would use bromine water to distinguish between an alkane and an alkene, and give the result for each.
Hard
55.Explain why fermentation stops once the alcohol concentration reaches about 15%.
Hard
56.Explain why alkenes are described as unsaturated hydrocarbons and why they are more reactive than alkanes.
Hard
57.A student suggests that ethanol made by fermentation is chemically different from ethanol made by the hydration of ethene. Explain whether the student is correct.
Hard
58.Calculate the relative molecular mass (Mr) of ethanol, C2H5OH. (relative atomic masses: H = 1, C = 12, O = 16)
Medium
- A51
- B56
- C46
- D41
59.Butene reacts with steam to produce butanol: C4H8 + H2O → C4H9OH. Calculate the maximum mass of butanol, in kg, that can be produced when 1.4 kg of butene reacts with excess steam. (relative molecular mass of butene, C4H8 = 56; relative molecular mass of butanol, C4H9OH = 74)
Medium
- A1.85 kg
- B2.85 kg
- C0.85 kg
- D3.85 kg
60.A student burns propan-1-ol in a spirit burner to heat 100 g of water. The temperature of the water rises by 20 °C. Using Q = m × c × ΔT with c = 4.18 J g⁻¹ °C⁻¹, calculate the energy transferred to the water in joules.
Medium
- A9196 J
- B10032 J
- C7524 J
- D8360 J
61.Butene undergoes complete combustion: C4H8 + 6O2 → 4CO2 + 4H2O. How many oxygen molecules, O2, are needed to completely burn one molecule of butene?
Medium
- A5 molecules
- B8 molecules
- C7 molecules
- D6 molecules
62.In a calorimetry experiment, 100 g of water is heated by burning an alcohol. The temperature of the water rises by 25 °C. Calculate the energy transferred to the water in joules. Use Q = m × c × ΔT, where c = 4.18 J g⁻¹ °C⁻¹. Give your answer to the nearest whole number.
Medium
- A12540 J
- B9405 J
- C11495 J
- D10450 J
63.A spirit burner containing ethanol loses 0.56 g of mass while heating 100 cm³ of water and raising its temperature by 40 °C. Calculate the energy released per gram of ethanol burned. Use Q = m × c × ΔT with c = 4.18 J g⁻¹ °C⁻¹, and give your answer in kJ/g to 1 decimal place.
Medium
- A29.9 kJ/g
- B32.9 kJ/g
- C26.9 kJ/g
- D35.9 kJ/g
64.Calculate the relative molecular mass (Mr) of propanoic acid, CH3CH2COOH. (relative atomic masses: H = 1, C = 12, O = 16)
Medium
- A74
- B81
- C67
- D88
65.A fermentation reaction produces 2.3 g of ethanol. Calculate the number of moles of ethanol produced. (Mr of ethanol = 46) Give your answer to 3 decimal places.
Hard
- A0.05 mol
- B1.05 mol
- C-0.95 mol
- D2.05 mol
66.Ethene reacts with steam to form ethanol: C2H4 + H2O → C2H5OH. Calculate the maximum mass of ethanol, in kg, that can be produced from 2.8 kg of ethene reacting with excess steam. (relative molecular masses: C2H4 = 28, C2H5OH = 46)
Hard
- A4.6 kg
- B3.6 kg
- C6.6 kg
- D5.6 kg
67.A sample of ethanol is burned completely: C2H5OH + 3O2 → 2CO2 + 3H2O. If 0.5 mol of ethanol is burned, what mass of carbon dioxide is produced? (Mr of CO2 = 44) Give your answer in grams.
Hard
- A40 g
- B48 g
- C44 g
- D52 g

Tarjetas

What is the functional group of an alkene?

The C=C double bond.

What is the general formula of the alkene homologous series?

CnH2n.

Why are alkenes described as unsaturated?

They contain a carbon-carbon double bond, so they have two fewer hydrogen atoms than the alkane with the same number of carbon atoms and can make more bonds by opening up the C=C bond.

Name the first four members of the alkene homologous series.

Ethene, propene, butene and pentene.

What is the molecular formula of ethene?

C2H4.

What is the molecular formula of propene?

C3H6.

What type of reaction do alkenes mainly undergo?

Addition reactions, in which atoms of a simple molecule add across the C=C double bond.

What happens to the C=C bond during an addition reaction?

It opens up and becomes a single carbon-carbon bond, allowing two more atoms to bond, one on each carbon.

What is the test for an alkene using bromine water?

Shake the compound with orange-yellow bromine water; if it is an alkene the solution decolourises.

What is the result of adding bromine water to an alkane?

The bromine water remains orange because alkanes are saturated and do not undergo addition reactions with bromine.

What are the conditions for the hydrogenation of an alkene?

Hydrogen gas at 150 °C with a nickel catalyst.

What is the product of the addition of hydrogen to an alkene?

An alkane.

What are the conditions for the hydration of ethene to produce ethanol?

Steam at around 330 °C and 60–70 atm pressure with a concentrated phosphoric acid catalyst.

What is the product of the addition of steam to an alkene?

An alcohol.

What are the conditions for the addition of a halogen to an alkene?

The reaction occurs readily at room temperature.

What is the product of the addition of chlorine to ethene?

1,2-dichloroethane, formed by the chlorine atoms adding across the C=C bond.

Why do alkenes tend to burn with a smoky flame in air?

They have a higher carbon to hydrogen ratio, so they tend to undergo incomplete combustion.

What are the products of the complete combustion of an alkene?

Carbon dioxide and water.

What is the functional group of an alcohol?

The hydroxyl group, -OH.

Name the first four members of the alcohol homologous series.

Methanol, ethanol, propanol and butanol.

What is the general formula of an alcohol?

CnH2n+1OH.

What are the conditions for producing ethanol by fermentation?

Sugar or starch is dissolved in water, yeast is added, and the mixture is kept between 15 and 35 °C with no oxygen for a few days.

Why is fermentation described as an anaerobic process?

Oxygen is not required; the yeast respires anaerobically, breaking down glucose to form ethanol and carbon dioxide.

What happens if the temperature is too high during fermentation?

The enzymes in the yeast become denatured and the reaction stops.

Why is ethanol production by fermentation a batch process?

The yeast is killed off once the alcohol concentration reaches about 15%, so the vessel is emptied and the process is started again.

How is ethanol separated from the fermentation mixture?

By fractional distillation, heating to 78 °C so ethanol evaporates and is condensed, leaving water and impurities behind.

What is the functional group of a carboxylic acid?

The carboxyl group, -COOH.

Name the first four members of the carboxylic acid homologous series.

Methanoic acid, ethanoic acid, propanoic acid and butanoic acid.

What is the general formula of a carboxylic acid?

CnH2n+1COOH.

What happens when a carboxylic acid is added to water?

It dissolves to form a weakly acidic solution.

What are the products when a carboxylic acid reacts with a carbonate?

A metal salt, water and carbon dioxide gas.

What is the name of the reaction between an alcohol and a carboxylic acid?

Esterification, which produces an ester and water and needs an acid catalyst such as concentrated sulfuric acid.

What is the functional group of an ester?

R-COO-R.

What are esters used for?

They are sweet-smelling oily liquids used in food flavourings and perfumes, and they are volatile so they vapourise easily.

Why are carboxylic acids described as weak acids?

They only partially ionise in water, forming an equilibrium in which most molecules remain undissociated, giving pH values between 3 and 7.

What is the difference between a saturated and an unsaturated compound?

A saturated compound has only single carbon-carbon bonds; an unsaturated compound has one or more carbon-carbon bonds that are not single.

What is a homologous series?

A family of similar compounds with the same functional group and general formula, differing by a –CH2– unit, with a trend in physical properties and similar chemical properties.

What is the product when ethanol is oxidised by acidified potassium dichromate?

Ethanoic acid; the potassium dichromate turns from orange to green during the reaction.

What is the word equation for the reaction of methanol with sodium?

sodium + methanol → sodium methoxide + hydrogen.

What is the balanced symbol equation for the complete combustion of ethanol?

CH3CH2OH + 3O2 → 2CO2 + 3H2O.

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