Key to Passing Highers Chem - UNIT 2

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which also has a branch attached (attached to a carbon with 3 other carbons bonded) R PROPERTIES OF ALCOHOLS: Alcohol containing two hydroxyl groups are called diols e.g. glycol - ethane-1,2-diol Alcohol containing three hydroxyl groups are called triols e.g. glycerol - propane-1,2,3,-triol As the number of hydroxyl groups increase, the boiling point tends to increase due to the molecule (hydroxyl group is part of) is polar which leads to the increase in hydrogen bonding present which means more energy is required break it. This increase meaning stronger intermolecular forces means higher melting and boiling points, increased viscosity, and an increased solubility in water or polar solvents. R² -C OH -R¹ Formed by reacting an alcohol with a carboxylic acid Known as esterification or condensation reaction as it is an example of two large molecules joining while eliminating a smaller molecules (water) Alcohol + Carboxylic Acid → Ester + Water Functional groups = ester link (-COO-) MAKING ESTERS: Made between alcohol and carboxylic acid by condensation Equal quantities of reactants added to test tubes Concentrated sulphuric acid added as catalyst A wet paper towel put around test tube (acts as the condenser) Test tube placed in water bath (not Bunsen burner as alcohol is flammable) CONDENSATION REACTION: Glycerol + Fatty Acids Fat Or Oil+ Water FATS: HYDROLYSIS REACTION: Fat Or Oil + Water → Glycerol + Fatty Acids wet paper towel held on with elastic band Reaction mixture poured onto sodium hydrogen carbonate solution to neutralise sulfuric acid and unreacted carboxylic acid Evidence ester is formed: distinct smell and two layers are formed USE OF ESTER: Flavourings and fragmentises due to pleasant fruity smells Solvents for non-polar compounds that do not dissolve in water HYDROLYSIS OF ESTER: Reactions of carboxylic acid and alcohol to make esters is reversible Ester + Water → Alcohol + Carboxylic Acid For hydrolysis, mixture are heated under reflux: heating mixture with a condenser attached This ensures volatile compounds do not escape and allows reaction to take place at higher temperatures SUMMARY: volatile (can easily vaporise), flammable, distinctive smells FATS AND OILS: Edible fats and oils are esters formed from a condensation reaction of glycerol + three fatty acid molecules - carboxylic acid. Each molecule of alcohol condenses with three molecules fatty acid. CH₂-OH hot water CH₂-OH carboxylic acid, alcohol and sulphuric acid H-C-OH + 3R-COOH OILS: Esterification Making an Ester Hydrolysis H CH₂ O 0 Glycerol + Fatty acids Triglyceride Glycerol has three -OH groups and form three ester links with fatty acid molecules. Products of this = triglyceride -R₂ + 3H₂O Note: one mole glycerol combines with three moles fatty acid FATTY ACIDS: Are saturated or unsaturated straight chain carboxylic acids (usually with a long chain of carbon atoms) Contains even number of carbons Structure for fatty acids which combine with glycerol affects whether fat or oil formed + Water ester making oily/solid layer water + sodium hydrogen- carbonate Saturation (single carbon to carbon bonds) Structure has efficient packing Stronger van der waals interactions Higher melting points than oils (more energy required to separate molecules) Hence are solids W wwwww Unsaturation (at least one carbon to carbon double bond) Distorted structure + cannot pack as closely Weaker van der waals Lower melting points (less energy required) Hence are liquids www.m www ww MMM mym -WWW DEGREE OF UNSATURATION IN FATS AND OILS: unsaturated compounds tend to quickly decolourise in bromine solution whereas saturated compounds like fats do not. Bromine molecule is added across carbon- carbon double bond in addition reaction. Greater number of double bonds in substance = more bromine solution can be decolourised. BROMINE SOLUTION: When oil is shaken in bromine solution - bromine waters' distinct brown colour decolourised. This indicates the presence of double bonds in oil molecules. When fats dissolve in organic solvents like hexane - bromine water' does not decolourise BUT sometimes only slight and slow decolourisations occur with fats still. This indicates fats have fewer / no double bonds to oil molecules. You can titrate fats / oils with bromine water and determine volume of bromine (inc. number of moles) needed to react with all double bonds in one mole fat / oil. Reaction ends when all double bonds used up = traces of bromine remain (brown colour → decolourised). IODINE SOLUTION: Degree of saturation in fats / oils can be determined through the lodine Number lodine reacts with carbon to carbon double bonds Greater iodine number = greater number of double bonds present CALCULATION UNTURATION: Saturated = No carbon-carbon double bond Monounsaturated = 1 carbon-carbon double bond. Polyunsaturated = more than 1 carbon-carbon double bond In these occurrences - consider only side chain in structure (ignore -COOH or -COOR): saturated if fits the general formula CnH2n+1: not saturated there is 1 double bond for each pair of hydrogens lost (2 x H) e) SOAPS, DETERGENTS, EMULSIONS SOAPS: Formed by alkaline hydrolysis (the break up) of fats and oils by sodium or potassium hydroxide through boiling under reflux condition. When hydrolysed under alkali condition (NaOH), the fatty acids immediately react with water soluble, ionic salt - soaps. During process - three molecules soap are made per glycerol 3:1 ratio of fatty acid : glycerol hydrophobic group H a soap H-C-0-OCC₁7H35 H-C-0-OCC₁7H35 + 3NaOH-H-C-0-H H-C-0-OCC₁7H35 T H Animal fat/oil EMULSIONS: Alkaline Hydrolysis of Fats/Oils H HIC-O-H Na+ Catalysis of hydrolysis are alkali: NaOH or KOH hence fatty acids formed are changed into sodium / potassium salts e.g. sodium stearate, C17H35COO-Na+ in a neutralisation reaction Soap are ionic and water-soluble STRUCTURE OF SOAPS: H-C-0-H HOW SOAP WORKS: (model answer) Soap molecules have ionic heads that are hydrophilic and soluble in water Soap molecules have non-polar tails that are hydrophobic and insoluble in water Aggregation separates oils / grease from the surface DETERGENTS: H Glycerol "HARD WATER" = high levels of dissolved metal ions When hard water is mixed with soap a precipitate reduces the cleaning action Precipitate known as "SCUM" + 3Na C₁H₁5COo Hydrophobic part: Tail- long, non-polar covalent hydrocarbon chain (on fatty acid). This part of soap molecule is soluble in non- polar compounds such as oil and grease. Sodium stearate (a soap) hydrophillic group Hydrophilic part: Head- ionic / polar group at end of soap molecule. Head is soluble in ionic and polar compounds such as water. Soapless detergents are like soaps as they have a hydrophilic head and hydrophobic tail. They remove oils and grease like soaps. Soapless detergents do not form scum with hard water, hence detergents are used in hard water areas. Contains small droplets of one liquid that is dispensed into another liquid Can be used to separate polar and non-polar separation between layers The addition of an emulsifier allows two otherwise immiscible layers to be mixed uniformly, dispensing an equal amount of each substance throughout entire volume. Hence, with the addition of an emulsifier the interfaces between oil and water create a stabilised emulsion The mixture exists as a stable emulsion for a reasonable time (only). EMULSION IN FOOD: Used in food by reacting edible oils with glycerol In formed molecules, only one or two fatty acid groups are linked to each glycerol backbone Hydroxyl group in emulsifier is hydrophilic; Fatty acid chain is hydrophobic Hydroxyl Group (hydrophilic) - dissolved in water AND Fatty Acids (hydrophobic) - dissolved in oil HENCE forming stable emulsion f) PROTEINS FUNCTION OF PROTIENS: Major structural material of animal tissue Maintenance and regulation of life processes Enzymes= proteins which act as biological catalysts AMINO ACIDS: Contains an amino group (amine) (-NH2) AND carboxyl group (-COOH) attached to same carbon Our bodies can make amino acids The amino acids our bodies cannot make are called ESSENTIAL AMINO ACIDS as they must be present in our diets AMIDE LINKS: CONDENSATION: Proteins are made of many amino acids linked together though condensation reaction The amino group of one amino acid and carboxyl group of another join, with the elimination of water The link formed in this condensation reaction is called a peptide link (-CONH-) Proteins which fulfil roles in our body are formed through different sequences of amino acids HYDROLYSIS: Proteins are broken up during our digestion by process called hydrolysis Produces amino acids by adding water molecules (breaking the N-C) If both peptide links are hydrolysed, three amino acids form CHROMATOGRAPHY: Amino acids can be identified by hydrolysing the proteins using chromatography water in →water out condenser in reflux position. concentrated HCI protein Hydrolysing Protein Acid 4 Protein P Heat paper- tank- solvent- Chromatographic Analysis of Protein xx ABPCDE pure amino acids. ABPCDE PROTEIN SHAPES: Proteins contain long-chain molecules held by hydrogen bonding When proteins are heated intermolecular bonds are broken, allowing protein to change their shape= denaturing Denaturing altering texture and appearance of food when cooked g) OXIDATION OF FOOD ALCOHOL: divided into three types depending on the -OH positioning: primary, secondary, and tertiary PROPERTIES: R-C=O H Aldehyde Alcohol molecules are polar hence hydrogen bonding exists Small alcohol molecules are miscible with water - hence molecules can form hydrogen bonding with another As number oh hydroxyl groups increase, boiling points increase More polar hydroxyl groups = more hydrogen bonding = more energy is needed to break them Also leads to higher melting points, viscosity, and solubility in water OXIDATION OF ALCOHOLS: Oxidation increase in oxygen to hydrogen ratio Reduction decrease in oxygen to hydrogen ratio PRIMARY ALCOHOL - 2 stage oxidisation H h R H H Primary alcohol SECONDARY ALCOHOL - 1 stage oxidation H + R ·0 H R Secondary alcohol - A, B, C, D and E are five known amino acids. - P is the hydrolysed protein. - P contains amino acids: A,B and D because those spots are present. - The hydrolysed protein also contains another one amino acid. -CIO Ketone - This can be identified by running another chromatogram with different known samples of O-H Carboxylic acid TERTIARY - no oxidisation possible (as they do not have a H atom attached to same carbon as a hydroxyl group) + R R H Tertiary alcohol Oxidisation in all primary and secondary alcohols contain carbonyl group (C=O) Oxidation results in an increase in oxygen to hydrogen ratio ALDEHYDES: CnH₂nO Functional group - carbonyl group e.g. butananl Functional group is always at end of chain with hydrogen atom attached KETONE: CnH₂nO Functional group - carbonyl group e.g. butanone Functional group is located in the middle of chain attached to -C- DISTINGUISHING BETWEEN ALDEHYDE AND KETONE, AND ALCOHOLS: Tests to distinguish between primary secondary and tertiary alcohols is that orange potassium dichromate reduces to a green chromate ion for primary and secondary but NOT tertiary. Test to distinguish between aldehydes and ketones is tollens regents forms a silver mirror and Fehling solution turns red; Both oxidised into a carboxylic acids for ONLY aldehydes. Oxidising agent Acidified potassium dichromate solution Fehling's solution Tollens' reagent Observations Orange Blue-green Blue solution → brick red precipitate Colourless → Silver (formation of a silver mirror) Explanation Cr₂O72 (aq) reduced to Cr3+ (aq) Cu²+ (aq) reduced to Cu₂O(s) i.e. Cu²+ + e → Cut Ag* (aq) reduced to Ag(s) i.e. Ag+ e Ag ANTIOXIDANT: easily oxidised substances that can undergo oxidisation in place of compounds they are added to as protection If molecules are oxidised - change in taste and flavour As oxidation of primary alcohols leads to carboxylic acid, so too does oxygen from air react with edible oils to produce a rancid flavour Antioxidants are molecules that can prevent oxidation from taking place Ascorbic acid (Vlitty C) will undergo oxidation and save food being oxidised Can be identified as substance being oxidised in REDOX h) FRAGRANCES ESSENTIAL OILS: concentrated extracts of volatile, non-water soluble (hydrophobic) aroma compounds from plants Used for perfumes, cleaning products, flavouring food, cosmetic product Extracted by plant source through steam distillation METHOD 1: oil is volatile, to ensure it evaporates, must use steam, a condenser must be fitted in - so the condenser can be used to cool down gas to form a liquid mixture of oil and water. As they do not mix, they can be easily separated TERPENES: Key compound of essential oils Unsaturated compounds formed together by joining isoprene units Isoprene = 2-methylbuta-1,3-diene (C5H8) General formula: (C5H8)n (n is number of isoprene links) (divide total number of carbon by 5 = number of isoprene units) OXIDATION OF TERPENES: i) SKIN CARE ULTRA-VIOLET LIGHT: Can be oxidised within plants producing compounds responsible for distinctive aromas of spices Preventing oxidation of terpenes: keep in brown glass bottle - filters light preventing chemicals degrading with light explosive hence altering properties and smell UV light is a high energy for of light present in sunlight Exposure to UV = molecules gaining enough energy for bonds to be broken This process explains sunburn and skin cancer and again of the skin Sun-block products prevent the UV reaching skin RADICALS: Thermometer Termination: radicals needed for this process - two radicals colliding = a stable compound = terminates process (2 R on LHS) FREE RADICAL SCAVENGERS: Molecules which react with free radicals to form table molecules and prevent chain reactions Are ddec cosmetics e.g. anti-aging cream, vitamin C + food products e.g. antioxidants, slowing oxid plastics. Mixture to be distilled Plant material and ant-bumping chips When UV light bond break- free radicals are formed Are the atoms which have unpaired electrons hence, very reactive SUMMARY OF RADICAL CHAIN REACTION: Initiation: starts reaction - bonds break forming two free radicals (2 R on RHS) Propagation: keeps reaction going - more radicals form allows the reactions continuance + chain reaction (1 R LHS/RHS each) Condenser n+ Essential o water