Unit 2 - Natures Chemistry Flashcards
Esters
carboxylic acid + alcohol —> ester + water
ester link: R-C–O/-O-R
condensation reaction: molecules join together with the elimination of a small molecule e.g. water
esterification reaction: an alcohol and carboxylic acid join together with the elimination of a small molecule e.g. water (reversible reaction)
hydrolysis reaction: molecule reacts with water and breaks down into smaller molecules
ester uses:
- food flavourings
- industrial solvents
- fragrances
Fats and oils
Fats and oils are concentrated sources of energy
They are naturally occurring esters called triglycerides
Produced when three fatty acids (long chain carboxylic acids) react with glycerol (aka. propan-1,2,3-triol)
Oils have a greater degree of unsaturation (have more carbon carbon double bonds per molecule) than fats:
- When the hydrocarbon is unsaturated the double bonds cause kinking in the chain meaning the chains of the molecule can’t pack close together leading to fewer intermolecular forces between the chain.
- This means oils have a lower melting point and is liquid at room temperature
Fats have a greater degree of saturation (less double bonds) than oils:
- When the fatty acid chains of the hydrocarbons are mostly saturated the chains of the molecule pack close together, with stronger intermolecular forces between the molecules
- this means that fats have a higher melting point than oils and is therefore solid at room temp
Hydrogenation: is the addition of hydrogen to double bonds of an unsaturated molecule, this can be carried out to saturate an oil into a fat (liquid -> solid)
Fats and oils are important for storing and transporting fat-soluble vitamins
Proteins
Proteins are compounds made up of carbon, oxygen, hydrogen and nitrogen
Proteins are condensation polymers made up of monomers called amino acids (amino acids are recyclable as they can be reused/ broken down into other amino acids n waste products)
amino acid:
H/H-N-(Carbon chain)-C–O/-OH
[amine group-/-carboxyl group]
Essential amino acids:
The body is not capable of making all the possible amino acids required to make all body proteins so is dependent on dietary proteins to supply certain (“essential”) amino acids
Protein molecules contain amide (/peptide) links:
/\/\/\/C–O/N-H\/\/\/\
Hydrogen bonding occurs between polymer chains when forming a protein
A hydrolysis reaction splits a protein down into amino acids, and breaks the hydrogen bonding
A condensation reaction builds up amino acids into proteins
The amino acids present in a sample of proteins can be identified by hydrolysis (to split up compound) and then carrying out paper chromatography
Enzymes are proteins and when denatured the shape of their active site is altered and the hydrogen bonding is broken
Condensation polymerisation
Polyamides are an example of condensation polymers
A condensation polymerisation reaction is when two different monomers each with two functional groups (such as diacids/ diamines/ dialcohols/ dicarboxylic acids) react together resulting in a polyester, as well as a small molecule which can easily be removed (e.g. water)
Addition polymerisation
when monomers each with only one functional group react together to form a polymer (the only product formed)
Aldehydes
Aldehydes are molecules responsible for many flavours and aromas
Aldehyde functional group:
R-C–O/-H
(contains the carbonyl group: C–O), and is located at the end of the molecule’s carbon chain
Aldehyde names end in ‘-al’ (eg. methanal)
Aldehydes can be oxidised (to form carboxylic acids)
Ketones
Ketones are molecules used as solvents, varnishes and plastics
Ketone functional group: (essentially a carbonyl group)
R-C–O/-R, and is located in the middle of the molecule’s carbon chain
Ketone name ends in ‘-one’ (e.g. methanone, butan-2-one)
Ketones have a higher boiling point than aldehydes
Ketones cannot be oxidised
Oxidising agents
Benedicts/ Fehlings solution: blue solution –> orange-red precipitate
Tollens reagent: colourless –> silver
Acidified potassium dichromate: orange solution –> green solution
Acidified potassium permanganate: purple –> colourless
Copper (II) oxide and heat: black oxide –> reddish copper metal
(using these oxidising agents can be used to test whether a compound is an aldehyde or a ketone as if a reaction does not occur it is a ketone)
Alcohols
Primary alcohol: the carbon attached to the -OH functional group is also bonded to two hydrogens
Secondary alcohol: the carbon attached to the -OH functional group is also bonded to one hydrogen
Tertiary alcohol: the carbon attached to the -OH functional group is bonded to no other hydrogen atoms
Oxidation of alcohols
The oxidation of alcohols means an increase in the oxygen:hydrogen ratio
primary alcohol –[O]-> aldehyde –[O]-> carboxylic acid
secondary alcohol –[O]-> ketone
tertiary alcohol: not easily oxidised
Rancidity
When a food product (that contains edible oils) reacts with oxygen the oils undergo oxidative rancidity causing them to become sour tasting and ‘rancid’
To prevent this when food is packaged nitrogen rather than oxygen can be used to fill the package (e.g. in crisp bags)
Soap
Soap is formed via saponification , which involves the hydrolysis of esters (of which are present in fats and oils)
soap molecule:
/\/\/\/\/\/C–O/O3Na
Has an ionic, hydrophilic (water-soluble) head and a covalent, hydrophobic (fat-[grease]-soluble) carbon chain tail
How soap works:
The hydrocarbon tail sticks into the the grease molecule, causing the ionic head to cover the surface of the grease creating a barrier of negative charges, due to this the grease droplets repel each other and are carried away, removing the dirt
Soaps, however, are not very water-soluble so only tend to work in hot water. Additionally in ‘hard’ water (which contains a relatively high concentration of magnesium and chlorine ions) soap will produce a layer of ‘scum’
Detergent
Detergent molecule:
/\/\/\/\/\/\/S–O/–O/-O/-ONa
Has an ionic, hydrophilic (water-souable) head and a covalent, hydrophobic (fat-soluble) tail
Detergents are much more soluble in water then soap, and don’t form ‘scum’ in hard water
Emulsion
An emulsion contains small droplets of one liquid dispersed in another
Emulsifiers are soap-like molecules that cause an emulsion to be formed
This is required for the ‘mixing’/ ‘dissolving’ of immiscible substances
Oil-in-water emulsion:
The hydrocarbon tail sticks into the the oil molecule, causing the ionic head to cover the surface of the oil molecule and creating a barrier of negative charges, causing the oil droplets to remain ‘dissolved’
(in this example the oil is the dispersed phase and the water is the continuous phase)
Synthetic emulsifiers:
When partial hydrolysis of fats and oils occurs/ edible oils are reacted with glycerol, mono-/ di-glycerides (which act as emulsifiers) are formed.
Emulsifiers are used in maintaining the quality/ freshness/ texture of foods, and prevents mould growth.
Demulsifiers do the opposite of emulsifiers.
Ultraviolet (UV) radiation
Utraviolet radiation (UV) is a high-energy form of electromagnetic radiation and is present in sunlight
Exposure to UV light can result in sunburn, skin ageing, skin cancer
Sun-protection creams prevent the damage from UV light:
- sun block… prevents UV radiation penetrating the skin via inorganic materials that reflect/ scatter UV
- other protection creams contain organic chemicals that are often dissolved in oils and absorb UV radiation
