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Higher chemistry based off course support notes > Unit 2 > Flashcards

Unit 2 Flashcards

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1
Q

Define the term functional group of a molecule?

A

The functional group of a molecule refers to the group of atoms or bonds that are responsible for the chemical reactivity of a molecule

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2
Q

State the functional group that is responsible for the reactivity of the alkanol homologous series (alcohols)?

A

The hydroxyl group is the functional group present in alcohols.

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3
Q

What rule must be followed when naming a compound that has a functional group?

A

When a chemical has a functional group this means that the functional group must be numbered the lowest possible number in the chain.

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4
Q

State some common uses of alcohols?

A

Alcohols have uses as fuels due to their ease of combustion and renewability

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5
Q

State some examples of uses of carboxylic acids?

A

Carboxylic acids can be commonly used as preservatives, they can be used to make soap and they have many uses in medicine.

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6
Q

State the functional group that can be found in the carboxylic acids?

A

The carboxylic acids have a Carboxyl functional group which is responsible for their chemical reactivity as a homologous series

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7
Q

Explain what is meant chemically by a salt?

A

A salt is the product of any reaction between any acid and any alkali, when an acid and an alkali react together this is called a neutralisation reaction and water is produced. Note that if a carboxylic acid is used then the salt’s name will end with ‘oate’

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8
Q

State the purpose of esters in nature?

A

Esters can be found in many fruits, vegetables and flowers. Esters give these substances flavour.

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9
Q

State some of the uses that we have for man made esters?

A

Esters can also be man made and used as artificial flavours, solvents for paints and varnishes, and as an ingredient for perfumes.

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10
Q

State the name of the type of reaction that is undergone to produce an ester?

A

Esters are produced in condensation reactions between alcohols and carboxylic acids. This type of condensation reaction could also perhaps be referred to as an esterification reaction.

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11
Q

Explain what is meant by a condensation reaction?

A

A condensation reaction is a reaction where two molecules combine together in order to form a larger molecule as well as the loss of a water molecule.

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12
Q

Can esterification (condensation) take place without the presence of a catalyst?

A

No, esterification requires the presence of a concentrated sulfuric acid catalyst as the reaction is reversible and the catalyst is good at absorbing the water produced by the esterification which by Le chatelier’s principle will prioritise the forwards reaction to take place.

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13
Q

How can we obtain the original alcohol and carboxylic acid used to prepare the ester?

A

To do this we can use a hydrolysis reaction to break down the ester into the components that make up the ester.

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14
Q

Explain what is meant by a hydrolysis reaction?

A

A hydrolysis reaction refers to a reaction in which a larger molecule reacts with water and is broken down into smaller molecules.

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15
Q

What are the rules that chemists use when they are naming an ester?

A

When naming an ester we must consider that each ester has two parts to its name. The first part of the esters name comes from the alcohol that was used to produce it and will end with the prefix ‘yl’
The second half of the esters name is derived from the carboxylic acid that was used to produce it and will end with the prefix ‘oate’.

Esters are named based on how many carbons are in each alcohol and carboxylic acid used in the condensation reaction e.g a reaction between ethanol and Butanoic acid would produce
Ethyl Butanoate.

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16
Q

State the functional group that can be found in all esters?

A

All esters contain a carboxylate functional group this carboxylate functional group is responsible for the chemical reactivity of the esters.

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17
Q

What is an alternative name given to the carboxylate functional group?

A

The carboxylate functional group can alternatively be called the ester link.

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18
Q

Explain what happens during a condensation reaction?

A

During a condensation reaction the hydroxyl group detaches from the carboxylic acid and the hydrogen molecule detaches from the alcohol and they will combine to form water and the remaining bonds in the carboxylic acid and water will then form the ester link (Carboxylate group)

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19
Q

Explain what happens during a condensation reaction?

A

During a condensation reaction the water molecules attack the carboxylate group (ester link) causing the carboxyl group and the hydroxyl group to reform. This breaks down the larger ester molecule into smaller molecules of alcohol and carboxylic acid.

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20
Q

What general rule can we use to identify the carboxylic acid and alcohol that would be produced when we hydrolyse an ester?

A

We can identify the carboxylic acid part as the side of the molecule that contains a double carbon to oxygen bond ( C=O )

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21
Q

State what type of molecules that fats and oils belong to?

A

Esters /triglycerides

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22
Q

Explain the reason why fats and oils are an essential part of our diets?

A

Fats and oils are an essential part of our diets as they are a concentrated source of energy

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23
Q

Give examples of the three main sources of fats and oils?

A
  • Animal fats/oils
  • Vegetable fats/oils
  • Marine fats/oils
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24
Q

Since fats and oils are esters they have an alcohol part and a carboxylic acid part, what is the chemical name for the alcohol found in all fats and oils?

A

The alcohol that can be found in every fat or oil is called propan - 1,2,3 - triol. The short name for this molecule is glycerol. The molecule contains three hydroxyl groups hence the ‘triol’

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25
State the name that is given to the carboxylic acids used to produce fats or oils?
Fatty acids is the name for the acids that are used to form fats and oils.
26
Explain why fats and acids may sometimes be referred to by the name of triglycerides?
Acids and alcohols are sometimes referred to as triglycerides as they contain one molecule in all of their structures and each fat or oil is also made of of three fatty acids.
27
Explain what is meant by a saturated fatty acid?
A saturated fatty acid is a fatty acid that has no C=C double bonds in its structure
28
Explain what is meant by a monounsaturated fatty acid?
A monounsaturated fatty acid is a fatty acid that contains only a single C=C double bond in its structure.
29
Explain what is meant by a polyunsaturated fatty acid?
A polyunsaturated fatty acid refers to a fatty acid that has many C=C bonds throughout its structure.
30
Explain why Fats are solids at room temperature?
Fats are molecules that tend to be saturated, this saturated structure means that fat molecules are tightly packed together. This increases the strength of the intermolecular forces involved in holding the fat molecules together increasing the melting and boiling point of the fats.
31
Explain why oils are liquids at room temperature?
Oils are liquids at room temperatures because oils tend to be more unsaturated than fats. The carbon to carbon double bonds that are present in the oils cause the carbon chains to kink. This kinking effect causes the molecule to be less tightly packed meaning that the strength of the intermolecular forces is weaker than in a fat. Hence the weaker intermolecular forces between molecules of oils lower the melting point and the boiling point of the oil.
32
Explain what is meant by a soap?
Soaps are sodium salts of fatty acids which are formed by the alkaline hydrolysis of a fat or oil.
33
What must be present during the process of hydrolysing a fat or an oil to produce a soap?
A sodium alkali must be present such as sodium hydroxide that allows the alkaline hydrolysis to take place in which the carboxylic acids formed by hydrolysis will immediately undergo neutralisation with the alkali and produce the sodium salt known as soap, water will also be produced.
34
State the term commonly used to describe a reaction that yields soap?
Saponification
35
Explain why vegetable oil is said to be immiscible with water?
As vegetable oil does not mix with water and they will always seperate out into two distinct layers because of the intermolecular bonding involved in each of the molecules. Vegetable oils are esters and so they are nonpolar where water is a polar molecule hence the two liquids will not dissolve in one another.
36
Explain why water is ineffective at removing greece?
As most greece is a form of fat or oil and is nonpolar where water is a polar molecule. The van der waals forces involved in each of the molecules cause the liquids to be immiscible.
37
Explain what is meant by an emulsion?
An emulsion is a term used to describe how a liquid will be dispersed into another liquid.
38
What term can be used to describe the chemical role that soaps have when removing grease?
Soaps are described as Emulsifying agent or Emulsifiers
39
What is meant by the term emulsifying agent or emulsifier?
An Emulsifying agent is a term used to describe a chemical that stabilises emulsions and prevents them from separating out
40
Describe the head of a soap molecule?
The ionic head of a soap molecule is defined as being hydrophilic meaning water loving and will dissolve in the water
41
Describe what is meant by the tail of a soap molecule?
The tail of a soap molecule is described as being hydrophobic meaning water hating. The tail of a soap molecule is nonpolar covalent and due to it being nonpolar it will attract the molecules of dirt and grease that water is unable to remove.
42
Explain the process by which soap acts and the reason why soaps are called emulsifiers?
- When water is added to the soapy grease mixture the sodium ions dissolve in the water and separate from the rest of the soap molecule. Leaving the nonpolar covalent tail attached to the negatively charged head. - The covalent nonpolar tails attach to the nonpolar grease molecules due to the similar intermolecular forces involved. - When the substance is stirred or agitated this creates droplets with nonpolar covalent tails in them. These droplets are called miccells. - These micelles are prevented from separating out and forming larger molecules of grease due to the negative charges of the heads of the molecules repelling one another. - These micelles are an example of an emulsion as they are molecules of grease dispersed in the water. Hence soaps can be described as emulsifying agents as they prevent emulsions (micelles) from separating out and forming larger molecules of grease.
43
Explain what a detergent is and why one might be used?
A detergent is a sulfate based salt that acts as an emulsifying agent however prevents the formation of scum in water. As when using soap the sodium ions might react with impurities in the water to form a substance known as scum. The sulfate ions however do not react with impurities in the water
44
Explain why some types of foods can be described as emulsions?
As certain types of food are simply a mixture of fat or oil and water with an added emulsifier to keep the emulsion stable and prevent the components from separating out. An example of a type of food that can be described as an emulsion is mayonnaise.
45
Describe the structure of Emulsifiers used in food?
Typically the emulsifiers used in food will be monoglycerides meaning that they contain one ester link, other emulsifiers can be described as diglycerides as they will have two ester links. These molecules work as emulsifying agents because they like soaps have two very different parts of their molecule with the hydroxyl groups being polar and the ester links and associated fatty acids being nonpolar covalent.
46
Under what conditions should alkaline hydrolysis be carried out under and why?
Alkaline hydrolysis should be carried out under reflux conditions this can be done to prevent any of the volatile components from evaporating and being lost from the reaction mixture.
47
State the elements of which proteins consist of?
Carbon, Oxygen, Hydrogen, and Nitrogen
48
State the key element for protein formation?
Nitrogen
49
Explain what the process of digestion does to proteins?
Digestion is the process by which the body hydrolyses the proteins breaking them down into smaller molecules called amino acids by the action of water.
50
State the use that our bodies have for the amino acids obtained from digestion?
Our bodies use these amino acids to produce the proteins that our bodies require and these new proteins are essential for the growth and repair of new body tissue.
51
State the functional groups that an amino acid will contain?
- Carboxyl group - Amino group/Amine group These functional groups are responsible for the chemical reactivity of these molecules
52
What type of reaction is undergone that allows the body to produce new proteins from the amino acids obtained by digestion?
A condensation reaction occurs to allow these smaller amino acids to be built up into this larger protein molecule, this involves the loss of a water molecule.
53
What types of proteins are vital for this condensation reaction to occur forming new proteins?
Enzymes are very important in the condensation of amino acids into proteins
54
State what is meant by an enzyme?
Enzymes are biological catalysts that lower the activation energy required for a reaction to take place by providing an alternative route for the reaction.
55
What is the name of the functional group that can be found in protein molecules?
The functional group that is responsible for the chemical reactivity of the proteins is called an Amide link, (in certain cases can be called a peptide link however not always and so it is safer to use the term amide link)
56
State what is meant by essential amino acids?
Essential amino acids are amino acids that we must acquire through our diets
57
Explain the reason why food is said to 'go off'?
When food 'goes off' this is a result of an oxidation reaction as the food molecules have reacted with molecules of oxygen in the air.
58
What description can be given to a fat or an oil that has undergone oxidation?
When a fat or an oil undergoes oxidation it is described as being rancid.
59
State the names of the different types of alcohols?
- Primary alcohols - Secondary alcohols - Tertiary alcohols
60
Explain what is meant by a primary alcohol?
A primary alcohol describes an alcohol where the hydroxyl group is attached to a carbon that is attached to two other hydrogen atoms One carbon is attached to the carbon containing the hydrogen atom
61
Explain what is meant by a secondary alcohol?
A secondary alcohol is an alcohol were the hydroxyl group is attached to a carbon atom that contains one atom of hydrogen. Two carbon atoms attached to the carbon atom containing the hydroxyl group
62
Explain what is meant by a tertiary alcohol?
A tertiary alcohol describes an alcohol were the hydroxyl group that is attached to a carbon atom that does not have any direct bonds to a hydrogen atom. Three carbon atoms attached to the carbon that contains the hydroxyl group.
63
What oxidising agents can we use to illustrate how alcohols oxidise?
To determine which types of alcohols oxidise we can use acidified potassium dichromate, or we alternatively may wish to use copper(II) oxide as an oxidising agent.
64
Explain the changes that occur when a primary alcohol is oxidised?
Primary alcohols will oxidise to produce aldehydes, which only exist very temporarily before being further oxidised into carboxylic acids
65
Explain the changes that occur when a secondary alcohol undergoes oxidation?
When a secondary alcohol undergoes oxidation ketones will be produced. Ketones will not oxidise any further
66
Explain the changes that occur when a tertiary alcohol undergoes oxidation?
Tertiary alcohols are not readily oxidised
67
Explain how the oxygen to hydrogen ratio can help us to identify if an oxidation reaction has taken place?
If an oxidation reaction has taken place then this will result in an increase in the carbon to oxygen ratio. As oxidation means that there will be an increase in the number of oxygens and a decrease in hydrogens
68
Explain how the oxygen to hydrogen ratio can be used to help us identify if reduction has taken place?
If reduction has taken place then this will result in a decrease in the oxygen to hydrogen ratio. As reduction will decrease the number of oxygens causing the oxygen to hydrogen ratio to decrease.
69
Explain what it means if the oxygen to hydrogen ratio of a reaction has stayed the same?
If the oxygen to hydrogen ratio has stayed the same then this means that neither reduction or oxidation have taken place.
70
State the functional group that can be found in the aldehydes?
The carbonyl functional group can be found present in the aldehydes (C=O)
71
Which oxidising agents are typically used to distingush between ketones and aldehydes
- Benedict's solution - Tollens reagent
72
State the functional group present in the ketones?
Carbonyl functional group (C=O)
73
Explain the differences between an aldehyde and a ketone?
Aldehydes are able to oxidise whereas ketones do not undergo oxidation. Aldehydes have their functional group attached to one Alkyl group. Whereas the ketones functional group is attached to two carbons and therefore two Alkyl groups.
74
State some examples of uses for aldehydes and ketones?
The carbonyl compounds such as aldehydes and ketones can be used often as flavour molecules. Not only esters can be used as flavour molecules.
75
Explain what is meant by the term volatility?
Volatility refers to how easily a molecule evaporates, for instance molecules that have a high volatility have low melting and boiling points.
76
Explain what happens to the volatility of molecules as their molecular size increases?
As molecular size increases this causes volatility to decrease as the van der waals forces involved in a molecule increase as the size of the molecule increases hence the molecule will not evaporate as easily.
77
State what properties of chemicals must be taken into account when cooking?
When cooking you should take into account the solubility of flavour molecules and the volatility of flavour molecules.
78
Explain why solubility of flavour molecules should be taken into account when we cook a meal?
If this is not taken into account and water soluble flavour molecules are cooked in water then the flavour molecules will dissolve in the water removing the flavour from the food.
79
Explain why volatility of flavour molecules must be taken into account when cooking food?
As if volatility of flavour molecules is not taken into account and certain flavour molecules are volatile then by cooking the food at high temperatures the flavour molecules will be lost, instead these types of foods should be steamed or boiled in water.
80
Explain what is meant by denaturing of an enzyme?
When proteins are heated to a certain temperature they are denatured meaning that their shape is permanently changed as a result of the hydrogen bonds holding the polypeptides together being broken down this changes the shape of the active site of the enzyme and prevents the substrate from being able to bind to it.
81
State ways in which we can prevent food products from "going off" (oxidising)?
- Wrapping the food in cling film preventing oxygen in the air from coming into contact and reacting with the food molecules - Keeping the food in the fridge, slowing down the rate of the reactions taking place helping to preserve the quality of the food - Add antioxidants to foodstuffs to prolong their shelf lives.
82
Explain the role of antioxidants?
Antioxidants are molecule that will reduce the rate of oxidation reactions of food molecules by themselves undergoing oxidation and losing electrons to prevent the food molecules from undergoing oxidation
83
State some uses of essential oils?
- Perfumes - Cosmetics - soaps - flavouring food - flavouring drinks - household cleaning products
84
What are the major components of essential oils?
The major component of essential oils are called terpenes
85
On which type of molecule are terpenes based?
Terpene molecules are made up of many smaller isoprene molecules
86
State the chemical formula for an isoprene molecule?
( C5H8 )
87
State the molecular name for isoprene?
2-methylbuta - 1,3 - diene
88
What can terpenes be oxidised to become?
When we oxidise a terpene molecule they become a molecule called a terpenoid.
89
What functional groups does a terpenoid molecule contain?
A terpenoid molecule contains both a Hydroxyl functional group (OH) and a Carbonyl functional group (C=O)
90
What prefix is used at the end of the name of an aldehyde?
"al" e.g methanal
91
What prefix is used at the end of the name of a ketone?
"one" e.g propanone
92
What does the prefix at the end of a terpene or terpenoid indicate?
The ending of the terpene molecules name indicates the type of functional group present e,g "ene" - alkene group ( C=C ) "ol" - Hydroxyl group ( OH )
93
Define the term free radical?
Free radical is a term that is used to describe a highly reactive atom or group of atoms that contain unpaired electrons. The unpaired electrons make free radicals unstable and need to attack other atoms to obtain electrons to complete the electron pair.
94
When are free radicals likely to be formed (not always)?
Free radicals are likely to be formed when the bonding involved is essentially nonpolar.
95
Define the term free radical scavengers?
The term free radical scavengers describes molecules that react with free radicals to form stable molecules Note that free radical scavengers can also be added to food products to prevent oxidation reactions that are caused by free radicals as well as reaction with oxygen.
96
State the three steps of a Free radical chain reaction?
- Initiation - Propagation - Termination
97
Explain what happens during the initiation stage?
The initiation stage requires UV light and this is the stage when a free radical will be formed due to the UV light.
98
Explain the Propagation stage?
The Propagation stage describes how free radicals react with stable molecules to form more free radicals this process occurs over and over again and leads to a chain reaction
99
Explain the termination stage?
In this stage the free radical scavengers present in many commercial products mop up the free radicals and react with them to form stable molecules.
100
Explain the order in which the ingredients of sunscreen or sun block will be written?
The ingredients will be written in descending order of their weight

Higher chemistry based off course support notes (4 decks)

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