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Chemistry A Level > 4.2 Alcohols, Haloalkanes and analysis > Flashcards

4.2 Alcohols, Haloalkanes and analysis Flashcards

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1
Q

What are alcohols?

A
  • saturated containing only single covalent bonds
  • have the general formula CnH2n+1OH
  • have a graduation in physical properties
  • have similar chemical properties
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2
Q

Where is the alcohol group attached in primary alcohols?

A

At the end of the chain

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3
Q

Where is the alcohol group attached in secondary alcohols?

A

To a carbon with two alkyl chains and one hydrogen atom

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4
Q

Where is the alcohol group attached in tertiary alcohols?

A

To a carbon with three alkyl chains attached

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5
Q

How does boiling point change as the chain length of alcohol increases?

A

The boiling point of alcohols increases as chain length increases because there is more surface area contact so the induced dipole-dipole forces are stronger. This means more energy is needed to overcome these forces so the boiling point is higher

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6
Q

Why is the boiling point of alcohols higher than their corresponding alkanes?

A

There are hydrogen bonds between the alcohol molecules. This is the strongest intermolecular force so more energy is needed to overcome this force and thus raising the boiling point

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7
Q

How is volatility (ability to evaporate) affected by boiling point?

A

Volatility increases as the boiling point decreases

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8
Q

Are alcohols soluble in water?

A

Water molecules are polar and so is the alcohol functional group which means alcohols are soluble in water as their molecules form hydrogen bonds with the water molecules

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9
Q

How is solubility affected by chain length?

A

As alkyl chain length increases, the solubility of the alcohol decreases- this is because aliphatic chains cannot form hydrogen bonds and this becomes a larger part of the chain

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10
Q

Why are alcohols used as fuels?

A

They undergo combustion by transferring their stored chemical energy into a usable form such as thermal energy

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11
Q

What does a primary alcohol form when heated gently with acidified potassium dichromate and what is the colour change?

A

Forms an aldehyde- colour change from orange to green

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12
Q

What does a primary alcohol form when heated strongly with potassium dichromate under reflux and what is the colour change

A

Forms a carboxylic acid- colour change from orange to green

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13
Q

What does a secondary alcohol form when oxidised using potassium dichromate under reflux and what is the colour change?

A

It will form a ketone- colour change from orange to green

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14
Q

Do tertiary alcohols oxidise? Why?

A

Tertiary alcohols can’t oxidise because the carbon doesn’t have any hydrogen atoms attached

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15
Q

What is esterification?

A

The chemical reaction used to make an Ester

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16
Q

What are esters?

A

Organic compounds that contain a -COOR functional group, where R is an alkyl chain

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17
Q

What are esters commonly used for?

A

The manufacture of foods because they have a pleasant, fruity smell. Small-molecule esters are used in industry as powerful solvents

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18
Q

How do you make an Ester?

A

By reacting an alcohol with a carboxylic acid in the presence of an acid catalyst

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19
Q

What happens during an esterification reaction?

A

The O-H bond in the alcohol and the C-O bond in the carboxylic acid are broken. New bonds are made between the H and O-H to form water. The remaining two species bond to form an Ester

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20
Q

How are esters named?

A
  • the first part is the bane of the alkyl chain that was attached to the alcohol group
  • the second part is the stem of the bane of the carboxylic acid with the suffix -oate
  • For example, methyl hexanoate
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21
Q

What is dehydration?

A

A chemical reaction in which water is lost from an organic compound

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22
Q

What is dehydration a type of?

A

Elimination reaction

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23
Q

What happens when alcohols are dehydrated ?

A
  • Water is eliminated to make an alkene.
  • This happens when an -OH group from one carbon atoms and a H atom on an adjacent carbon atom are lost to form a water molecule.
  • A pi bond forms between the two adjacent carbon atoms
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24
Q

What is halide substitution?

A

When halide ions such as Cl-, Br- and I- react with alcohols and the halide takes the place of the alcohol group to form a haloalkane

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25
Q

What acid catalyst is added in halide substitution with chloride and bromide ?

A

Concentrated sulphuric acid

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26
Q

What acid is used when iodide is reacted in halide substitution and why?

A

Phosphoric acid is used because sulfuric acid oxidises iodide ions to iodine so the yield of the desired iodoalkane is very low

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27
Q

What are haloalkanes?

A

Saturated organic compounds that contain carbon atoms and at least one halogen atom

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28
Q

Where is the halogen attached on a primary haloalkane?

A

At the end of the chain

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29
Q

Are haloalkanes polar? Why?

A

There is a large difference in electronegativities of carbon and all halogens. This makes the carbon-halogen bonds in haloalkanes polar- there is a partial positive charge on the carbon and a partial negative charge on the halogen atom

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30
Q

What are nucleophiles?

A

Electron-pair donors e.g. H20, OH- and NH3

31
Q

What are the two factors that affect reactivity in a reaction between a haloalkane and nucleophile?

A

The strength of the C-X bond- as you go down the halogen group, the atoms get larger which means that the bonding electrons are further away from the nucleus. This results in lower mean bond enthalpies and the C-X bonds are easier to break- which means it’s more likely to react in a nucleophilic substitution reaction

The polarity of the C-X bond- Electronegativity of the halogens decreases down the group which means the polarity of the C-X bond decreases going down the group. The molecules with the most polarity are more likely to react

32
Q

What is nucleophilic substitution?

A

A reaction where an atom or group of atoms is exchanged for a nucleophile. The nucleophile is attracted to the partial positive charge on a carbon atom and donates its lone pair of electrons to form a new covalent bond

33
Q

Describe the steps of hydrolysis

A
  • Nucleophilic substitution
  • If water is used one of the H-O bonds in a molecule undergoes heterolytic fission to produce the nucleophile OH-
  • This species attacks the electron-deficient carbon atom in the haloalkane molecule
  • Once the nucleophile has bonded to the haloalkane, the C-X bond undergoes heterolytic fission to produce a halide ion.
34
Q

How is the rate of hydrolysis measured?

A
  • Change of concentration of a reactant or product in a given time
  • Halide ions are produced in a hydrolysis reaction, which form a coloured precipitate of a silver halide when acidified silver nitrate is added
35
Q

Which haloalkane has the highest rate of hydrolysis and why?

A

C-I because the bond is weaker and easier to break

36
Q

What happens when a haloalkane is heated under reflux with an aqueous alkali?

A
  • An alcohol is made
  • This is a nucleophilic substitution reaction and an example of hydrolysis
  • The rate of reaction is faster than using water
37
Q

What are chlorofluorocarbons (CFCs) ?

A

CFCs are a class of organic compounds that contain chlorine atoms and fluorine atoms

38
Q

Why are CFCs useful?

A

They are inert so they can be used in fire-fighting equipment and have domestic uses such as refrigerants because they are non toxic

39
Q

What happens when CFCs disperse into the atmosphere ?

A
  • They become exposed to UV radiation in the stratosphere

- The C-Cl bonds in C2F2Cl undergo homolytic fission due to UV light

40
Q

What does prolonged exposure to UV-B lead to?

A

Cell mutations which can cause skin cancer and cataracts

41
Q

What do chlorine radicals from CFCs do?

A

Catalyse the decomposition of ozone to make diatonic oxygen

42
Q

What do nitrogen and oxygen make in high temperatures?

A

Nitrogen oxides. Nitrogen monoxide can decompose ozone

43
Q

What is distillation?

A

A separating technique and is often used to collect a product from an organic synthesis reaction

44
Q

What equipment do you need for a distillation reaction?

A
  • a round-bottomed flask for a mixture
  • a thermometer holder
  • a thermometer
  • a condenser
  • a connector
  • a collecting flask
45
Q

How do you carry out distillation?

A
  • Connect the condenser to the water supply by attacking the bottom condenser hose to a water top, put the top rubber hose into the sink and turn on the water to give a gentle flow
  • Pur the organic mixture into the round-bottomed flask with a few anti-bumping granules to ensure smooth boiling
  • Heat the mixture using a Bunsen burner and collect the product, noting the temperature on the thermometer
46
Q

What is reflux?

A

A technique used in organic synthesis to ensure that a reaction mixture does not boil away

47
Q

What equipment do you need for a reflux reaction?

A
  • A pear-shaped flask
  • Bunsen burner
  • A condenser
48
Q

How do you separate immiscible liquids using a separating funnel?

A
  1. Mount an iron ring on a clamp stand and put the separating funnel in it
  2. Remove the stopper and make sure that the tap at the bottom is closed
  3. Pour the mixture into the funnel so that the funnel is no more than half full. Wash out the reaction vessel with water and add this to the mixture in the funnel
  4. Take the funnel out of the ring and invert it. Open the tap to equalise the pressure. Gently shake the mixture.
  5. Replace the funnel in the iron ring and give the mixture time to separate into layers
  6. Remove the stopper, put a beaker under the spout and open the tap. Collect the lower (water) layer in a beaker. Turn the tap off. As the organic product is in the upper layer, this aqueous layer can be in a beaker. The aqueous layer can be discarded.
  7. Using a clean, dry beaker, open the tap and collect the desired organic product
  8. Shake the liquid with a small amount of drying agent and pour the final dry product into a clean, dry container
49
Q

How is a drying agent used?

A
  • Add a few spatulas of the drying agent to the organic product
  • If the drying agent clumps together, add some more
  • When the drying agent remains free-moving the organic compound is dry
  • Use gravity filtration and collect the filtrate, which is the dry organic compound
50
Q

What is redistillation?

A

Redistillation is the purification of a liquid by performing multiple distillations.

51
Q

What happens when you add a few drops of bromine water to an unsaturated hydrocarbon?

A

It decolourises

52
Q

What happens when silver nitrate, ethanol and water are added to a haloalkane?

A
  • white precipitate indicates chloro-
  • cream precipitate indicates bromo-
  • yellow precipitate indicates iodo-
53
Q

What happens to ketones with the addition of acidified potassium dichromate?

A

No change

54
Q

What happens to aldehydes with the addition of acidified potassium dichromate?

A

Orange turns green

55
Q

What happens to ketones with the addition of Fehling’s solution ?

A

No change

56
Q

What happens to aldehydes with the addition of Fehling’s solution?

A

Dark red precipitate

57
Q

What happens to ketones with the addition of Tollens reagent?

A

No silver mirror

58
Q

What happens to aldehydes with the addition of Tollens reagent?

A

Silver mirror

59
Q

What happens when a universal indicator or pH prove is added to a carboxylic acid?

A

pH of a weak acid

60
Q

What happens when a reactive metal is added to a carboxylic acid?

A

Effervescence (hydrogen)

61
Q

What happens when a metal carbonate is added to a carboxylic acid ?

A

Effervescence (carbon dioxide)

62
Q

What happens when a warm volume of carboxylic acid and a few drops of H2SO4 is added to an alcohol?

A

Sweet smell of an ester after a short time

63
Q

What does the amount of vibration of a bond depend on? (3 things)

A
  • the bond strength
  • the bond length
  • the mass of each atom involved in the bond
64
Q

What does each peak on a infrared spectrum represent?

A

The absorbable of energy from infrared radiation that causes the vibration of a particular bond in a molecule

65
Q

How are alcohols identifies from an infrared spectrum?

A

The peak at 3230-3500 represents an O-H group in alcohols

66
Q

How are aldehydes and ketones identified from an infrared spectrum?

A

-the peak at 1680-1750 represents a C=O bond in both aldehydes and ketones

67
Q

How are carboxylic acids identified from infrared spectra?

A

It must contain two characteristic peaks:

  • a very broad peak at 2500-3300 which indicates the presence of the O-H group in a carboxylic acid
  • a strong, sharp peak at 1680-1750 that represents the C=O group in a carboxylic acid
68
Q

What are the stages of mass spectrometry?

A 
VIADD
Vaporisation 
Ionisation
Acceleration 
Deflection
Detection
69
Q

Explain how a mass spectrum is generated

A
  1. A vaporised sample is turned into positive gaseous ions
  2. They are then all accelerated to the same speed
  3. The ions are repelled by a charged plate
  4. The amount they are repelled tells us the mass of each ion
70
Q

What is the peak with the highest m/z value?

A

The total mass of the compound so the Mr

71
Q

What are the peaks with the lower m/z values ?

A

Fragments of the compound

72
Q

What are the fragment ions for these common m/z values:

  • 15
  • 17
  • 29
  • 43
  • 57
A
  • CH3+
  • OH+
  • C2H5+
  • C3H7+
  • C4H9+
73
Q

How can combined techniques be used to work out the compound being studied?

A

1) use the composition to work out the molecular formula
2) work out what functional groups are in the compound from its infrared spectrum
3) use the mass spectrum to work out the structure of the molecule

74
Q

Why do scientists use more than one analytical technique?

A

Some techniques may provide different data that can be used to reach the same conclusion

Chemistry A Level (6 decks)

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