Chemistry AS Textbook

NES/Chemistry/AS Topic 19 - Carboxylic Acids and Derivatives This topic introduces the chemistry of carboxylic acids and their derivatives. 19.1 Carboxylic acids a) describe the formation of carboxylic acids from alcohols, aldehydes and nitriles b) describe the reactions of carboxylic acids in the formation of: (i) salts, by the use of reactive metals, alkalis or carbonates (ii) alkyl esters (iii) alcohols, by use of LiAlH4 (iv) --A2 only-- c) --A2 only-- d) --A2 only-- e) --A2 only-- 19.2 --A2 only-- 19.3 Esters a) describe the acid and base hydrolysis of esters b) state the major commercial uses of esters, e.g. solvents, perfumes, flavourings 250

NES/Chemistry/AS 19.1 Carboxylic Acids Carboxylic acids contain the -COOH functional group. This does NOT mean that they have the properties of alcohols and aldehydes because of the -OH and -CHO groups. Carboxylic acids have their own properties and reactions. Carboxylic acids are weak acids, they only partly ionise. Chemical Properties of Carboxylic Acid Types of reaction: 1. Acid - Base 2. Reduction 3. Esterification (see Topic 17) 251

NES/Chemistry/AS 1. Acid - Base Carboxylic acids react with metals, bases, alkalis and carbonates just like regular strong acids. Type of Reaction Acid - Metal General Equation carboxylic acid + metal  salt + hydrogen Conditions none Example 1 2 CH3CH2COOH + Mg  (CH3CH2COO)2Mg + H2 Note - only metals above hydrogen in the reactivity series can react with carboxylic acids. Type of Reaction Acid - Base General Equation carboxylic acid + base  salt + water Conditions warm Example 2 2 CH3CH2COOH + MgO  (CH3CH2COO)2Mg + H2O Type of Reaction Acid - Alkali General Equation carboxylic acid + alkali  salt + water Conditions none Example 3 CH3COOH + NaOH  CH3COONa + H2O Type of Reaction Acid - Carbonate General Equation carboxylic acid + carbonate  salt + water + carbon Conditions dioxide Example 4 none 2 HCOOH + CuCO3  (HCOO)2Cu + H2O + CO2 252

NES/Chemistry/AS 2. Reduction Carboxylic acids can be reduced to aldehydes, then primary alcohols by a reducing agent. Type of Reaction Reduction General Equation carboxylic acid + [H]  primary alcohol + water Conditions LiAlH4 - dry ether - room temperature Example 5 CH3COOH + 4[H]  CH3CH2OH + H2O 253

NES/Chemistry/AS 19.3 Esters Esters contain the -COO- functional group. The formation and hydrolysis of esters is covered in Topic 17. Uses of Esters Esters usually have a sweet, fruity smell and are present naturally in fruits. The uses of esters is based on this:  Artificial flavours  Perfumes  Solvents (e.g. nail polish remover) 254

NES/Chemistry/AS Topic 22 - Analytical Techniques Analytical techniques are important tools for investigating organic compounds. 22.1 --A2 only-- 22.2 Infra-red spectroscopy a) analyse an infra-red spectrum of a simple molecule to identify functional groups (see the Data Booklet for functional groups required in the syllabus) 22.3 --A2 only-- 22.4 --A2 only-- 22.5 --A2 only-- 255

NES/Chemistry/AS 22.2 Infra-Red Spectroscopy This topic covers using infra-red spectroscopy to help identify unknown compounds - especially organic compounds. The machine used is called a spectrophotometer. A sample is placed in the spectrophotometer and infra-red radiation is passed through the sample. The energy absorbed corresponds to the changes in vibrational energy of the bonds between atoms. The infra-red spectrum produced can be used to identify functional groups in organic molecules.  Example 1: A typical infra-red spectrum for an organic compound. Each peak corresponds to a different functional group and can be identified with the data booklet. 256

NES/Chemistry/AS Properties of Peaks Peaks can have the following properties:  Absorbance Range  Width (Broad, or sharp)  Intensity (Strong, or Weak) Absorbance range is the wavenumber value of the peak, in cm-1. Width can be either broad for molecules with hydrogen bonding (alcohol, carboxylic acid), or sharp for carbonyl groups (aldehyde, ketone, ester). Intensity can be either strong, or weak for unsaturated hydrocarbons, nitriles, or amines/amides. This information is all in the table in the data booklet. Uses of Infra-Red Spectroscopy  Identifying unknown organic compounds  Method of detecting pollutants, and their concentrations, in the atmosphere The analysis of unknown organic compounds it not done using IR spectroscopy alone. In your examination questions you will also be provided with other information to help you identify the compound. Be aware that this type of question is difficult and will require higher order thinking skills. 257

NES/Chemistry/AS Topic 24 - Practical This topic is not on your syllabus as a separate topic, it covers all aspects of the practical course and is designed as preparation for the AS practical examination - Paper 3. Note - there is no data booklet for Paper 3. Decimal Markers In accordance with current ASE convention, decimal markers in examination papers will be a single dot on the line. Units In practical work, candidates will be expected to use SI units. In all examinations, where data is supplied for use in questions, candidates will be expected to use units that are consistent with the units supplied, and should not attempt conversion to other systems of units unless this is a requirement of the question. Units and Significant Figures Candidates should be aware that misuse of units and/or significant figures, i.e. failure to quote units where necessary, the inclusion of units in quantities defined as ratios or quoting answers to an inappropriate number of significant figures, is liable to be penalised in the assessments. Air hole closed Using a Bunsen burner Air hole half-open lighting the Bunsen burner Air hole open gentle heating strong heating 258

NES/Chemistry/AS Paper 3 Each paper will consist of two or three questions, totaling 40 marks. Question 1 is measurement based, as is Question 2 if there are 3 questions. The last question is analysis based. Question 1 (and 2) - Measurement The following are common experiments for the first question on the paper: 1. Titration, or measuring cylinders 2. Gas volume 3. Mass change 4. Temperature change 5. Rate of reaction 1 - Titration Titration is a method of very accurately mixing acid-alkali, or reagents for a redox reaction. Acid-Alkali Titrations General Method  Use a graduated pipette to add 25cm3 of acid, or alkali to a conical flask  Add indicator (enough drops to see the colour change)  Use a burette to add between 0.00cm3 and 50.00cm3 of the alkali, or acid to neutralise - you will see a colour change in the indicator. Your first titration is always a rough titration and is used as a guide to how much acid, or alkali, you need to add from the burette to get the colour change. After this you continue to do accurate titrations until you get two concordant result (within 0.10cm3) 259

NES/Chemistry/AS Indicators There are a variety of indicators that can be used including Indicator Colour in Acid Colour in Alkali Methyl Orange Red Yellow Bromophenol Blue Blue Thymol Blue Yellow Blue Thymolphthalein Yellow Blue Phenolphthalein Colourless Pink Colourless Some indicators have a 'middle colour' like bromophenol blue. This is because as the colour changes from yellow to blue, or blue to yellow a green colour can be seen which is a mix of yellow and blue. Follow the instructions carefully in the examination paper as to what colour you are looking for and if no instruction is given look for the middle colour. If in doubt, write down the volume on the burette and add a couple of drops to see what happens. Data CIE are very fussy about how the data tables are constructed. Rough Titration: Final Volume /cm3 Initial Volume /cm3 Titre /cm3 Accurate Titrations: 1 2 Final Volume /cm3 Initial Volume /cm3 Titre /cm3 260

NES/Chemistry/AS Marking Points:  Drawing the table correctly  Labeling the columns and rows correctly, with units  All data to 2 decimal places, with the second decimal place being a 0, or a 5  Concordant accurate titre values - you will lose this mark if you do another titration after getting concordant values  1-3 accuracy marks The next mark on the paper is for calculating the mean average of your two concordant accurate titre values. This mark is harder to get than you would expect. You must:  Tick the two concordant titre values in the accurate titrations table  Show your working out to two decimal places  Give your answer to two decimal places, with the second decimal place being a 0, or a 5 only. Calculation You will usually be asked to do a step by step mole calculation from your values. Always give answers (and working out) to 2 decimal places, or 3 significant figures. 261

NES/Chemistry/AS Errors and Improvements Apparatus Maximum Error (+ or -), cm3 Pipette 0.06 Burette 0.05 per reading* 2 dp Mass Balance 0.005 Measuring Cylinder with 1cm3 divisions 0.5 Measuring Cylinder with 10cm3 divisions 5 *These values are per reading. A burette always has 2 readings to get a titre value, so the error will always be (± 0.05cm3 x 2) = ± 0.10cm3. From the Maximum Error, the % Error can be calculated:  Example 1: Burette readings were taken during a titration, giving a titre value of 26.35cm3. Maximum Error = ± 0.05cm3 x 2 = ± 0.10cm3 % Error = = 0.380% The answer has been rounded to 3 significant figures. Improvements to experiments will vary widely. It is not possible to give a comprehensive list. These are common examples:  Use a burette, or graduated pipette instead of a measuring cylinder  Use greater volumes, or masses, to reduce % error 262

NES/Chemistry/AS Redox Titrations These are much like acid-alkali titrations. The main difference is that indicators are not often used as oxidising agents such as potassium manganate(VII) change colour during the experiment anyway. One indicator that can be used is starch for iodine/iodide redox reactions. 2 - Gas Volume Sometimes volume of gas produced is measured, using an inverted measuring cylinder in a bowl of water. 3 - Mass Change Sometimes mass change is measured during a thermal decomposition. A chemical is heated in a crucible and the mass is measured before and after heating. The data table must include all measured values, as well as any values that have been calculated.  Example 2 Data table for the thermal decomposition of a hydrated salt. M1 Mass of crucible + lid /g M2 Mass of crucible + lid + FB4 /g M3 Mass of crucible + lid + residue /g M4 Mass of FB 4 (M2 - M1) /g M5 Mass of residue (M3 - M1) /g M6 Mass of water lost (M4 - M5) /g Often 'heat to constant mass' is mentioned, or it is the answer for how to improve the experiment. This is when you heat the chemical, measure the mass and then heat the chemical again. If the mass is constant, stop heating, otherwise heat again to ensure that the reaction is complete. When heating hydrated carbonates, sulfates, sulfites, nitrates, nitrites and hydroxides - water will be given off first, but if the chemical is heated for too long, other gases can be given off as the chemical thermally decomposes. 263

NES/Chemistry/AS 4 - Temperature Change This is when an exothermic, or endothermic reaction takes place and the temperature difference is calculated. A graph of the data is usually plotted as two straight lines: corrected extrapolate back temperature rise T temperature (oC) chemical added at this time time (minutes) The value for ∆T can be read from the graph and then used in the following equations to calculate ∆H. Change in Energy: Where E is the energy change of the reaction mixture m is the mass of the reaction mixture* C is the specific heat capacity of the reaction mixture** ∆T is the change of temperature of the reaction mixture * The mass of the reaction mixture is considered the same as the mass of the water and as water has a density of 1g/cm3 then this value is the same as the volume of water used. ** The specific heat capacity of water is used, which is 4.18J/gK. 264

NES/Chemistry/AS Change in Enthalpy: Where ∆H is the change in enthalpy for the reaction E is the change in energy moles is the number of moles of the limiting reagent in the reaction Note - for a positive ∆T value, then the ∆H value will be negative and for a negative ∆T value, then the ∆H value will be positive.  Example 3 Calculate the change in enthalpy when 3g of zinc reacts with 25cm3 of excess copper(II) sulfate solution giving a temperature rise of 40.0oC. 265

NES/Chemistry/AS 5- Rate of reaction This usually involves timing a series of reactions in order to calculate the rate of a reaction. Where rate has the units s-1. 266

NES/Chemistry/AS Question 2 (or last question) - Analysis These questions involve you identifying unknown substances by carrying out analysis experiments. They are based on the qualitative analysis notes from the syllabus. Cations Cation(aq) Reaction with NaOH(aq) Reaction with NH3(aq) Al#+ White precipitate NH4+ White precipitate Insoluble in excess Ba2+ Soluble in excess Ca2+ Ammonia produced on No precipitate Cr3+ Cu2+ warming No precipitate Faint White precipitate is Fe2+ nearly always observed, Grey-Green precipitate Fe3+ unless reagents are pure Insoluble in excess Mg2+ White precipitate in high Pale Blue precipitate Mn2+ Ca2+ concentration Soluble giving a Dark Blue Grey-Green precipitate solution Zn2+ Soluble in excess Green precipitate, turning Brown on contact with air Pale Blue precipitate Insoluble in excess Insoluble in excess Red-Brown precipitate Green precipitate, turning Brown on contact with air Insoluble in excess White precipitate Insoluble in excess Insoluble in excess Red-Brown precipitate Off-White precipitate, rapidly turning Brown on Insoluble in excess contact with air White precipitate Insoluble in excess Insoluble in excess White precipitate Off-White precipitate, Soluble in excess rapidly turning Brown on contact with air Insoluble in excess White precipitate Soluble in excess When writing your observations you must copy these results word for word. It must be clear what the observations are when adding the chemical drop-by-drop and then when adding excess. It is possible that your analysis might include chemicals not in this list, in which case you may use your own descriptive words. 267

NES/Chemistry/AS Anions Anion Reaction CO32- Cl-(aq) CO2 liberated by dilute acids Br-(aq) I-(aq) White precipitate with Ag+(aq) NO3-(aq) Soluble in NH3(aq) Cream precipitate with Ag+(aq) NO2-(aq) Partly soluble in NH3(aq) Yellow precipitate with Ag+(aq) SO42-(aq) Insoluble in NH3(aq) NH3 liberated on heating with OH-(aq) SO32-(aq) and Al foil NH3 liberated on heating with OH-(aq) and Al foil --or-- NO liberated by dilute acids (not nitric acid)* White precipitate with Ba2+(aq) Insoluble in excess strong, dilute acid SO2 liberated on warming with dilute acid (not sulfuric acid) --or-- White precipitate with Ba2+(aq) Soluble in excess strong, dilute acid * The colourless NO(g) oxidises rapidly in air to Brown NO2(aq). For reactions that produce a gas, you are supposed to be ready with the gas test as well in order to prove the identity of the unknown chemical. You must also include the results of the gas test in your observations. Sometimes you will be asked to select a test to do based on the number of reagents involved - for example the sulfite ion can be tested for in two different ways: acid (one reagent); or Ba2+(aq) and acid (two reagents). When writing your observations you must copy these results word for word. It is possible that your analysis might include chemicals not in this list, in which case you may use your own descriptive words. 268

NES/Chemistry/AS Gases Gas Test and Test Result NH3 Turns damp red litmus blue White precipitate with limewater CO2 Soluble with excess CO2 Cl2 Bleaches damp litmus paper H2 'Pops' with a lighted splint O2 Relights a glowing splint SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless You are rarely directed to do a gas test, but you must be ready for them when doing tests for:  NH4+(aq)  CO32-  NO3-(aq)  NO2-(aq)  SO32-(aq) So you must be prepared to test for these gases when you:  add acid  add alkali (and possibly aluminium foil) Note - gases can also be made due to thermal decomposition when heating a chemical. 269

NES/Chemistry/AS Organic Analysis The following organic analysis notes are compiled from the syllabus, rather than being a separate list of tests. These will not appear at the end of the examination paper and must be learned. Functional groups used in organic analysis: Functional Group Reagent Result Alkane Bromine liquid/UV Alkene light Decolourises Halogenoalkanes Bromine water Alcohols Ethanol/Silver Decolourises Nitrate Aldehydes Oxidising Agent Precipitate / Solubility in Ammonia Oxidising Agent Fehling's Solution Colour change Tollens' Reagent Colour change Red precipitate 2,4-DNPH Silver mirror/Grey-black precipitate Yellow solution to Orange-Yellow Ketones 2,4-DNPH precipitate Oxidising Agent Yellow solution to Orange-Yellow Carboxylic Acids Sodium Carbonate precipitate Metal No Reaction Ethanol Oxidising Agent Effervescence (CO2) Any (2-ol) alcohol Effervescence (H2) Ethanal \"Iodoform\" Test No Reaction/Colour change Any (2-one) ketone Yellow precipitate Iodoform Test NaOH(aq) is added to a solution of iodine in potassium iodide solution until most of the colour has gone. The organic compound is warmed with this solution. A yellow precipitate forms. 270

NES/Chemistry/AS Alkane An alkane will decolourise bromine water (orange/brown) in sunlight. The reaction usually takes some time. Chlorine water (green) will also decolourise in diffuse (weak) sunlight and react explosively in strong sunlight. Alkene Alkenes will readily decolourise bromine water without the need for sunlight. Halogenoalkane Halogenoalkanes will hydrolise to form an alcohol and a halide ion. 1. The rate of the reaction can be used to identify the halide present. Chloroalkane Bromoalkane Iodoalkane Rate of hydrolysis Slow Medium Fast 2. The halide ion can be identified by the precipitate formed with the addition of Silver Nitrate solution after hydrolysis. Hydrolysis followed by: Chloroalkane Bromoalkane Iodoalkane Addition of AgNO3(aq) White ppt Yellow ppt Cream ppt ppt solubility in dil. ammonia Soluble Insoluble Soluble Slightly Insoluble ppt solubility in conc. ammonia soluble Soluble 271

NES/Chemistry/AS Alcohol Primary and secondary alcohols will oxidise in the presence of an oxidising agent. Oxidising Agent Colour of Oxidising Changes to Agent Green Potassium Chromate (VI) Orange Potassium Manganate Colourless (VII) Purple Tertiary alcohols cannot be oxidised Aldehyde 1. Aldehydes will oxidise in the presence of an oxidising agent. Oxidising Agent Colour of Oxidising Changes to Agent Potassium Chromate (VI) Green Potassium Manganate (VII) Orange Colourless Purple 2. Use Fehling's solution - The solution will change from a blue solution to a red precipitate. 3. Tollen's (Ammoniacal Silver Nitrate) - This solution can be made by adding silver nitrate solution with aqueous sodium hydroxide, giving a grey-brown ppt which must then be dissolved in aqueous ammonia. You may have to make this solution yourself in the practical examination - you will be instructed how to do this. The solution is then usually warmed before the aldehyde is added. The positive test result is a grey precipitate, or a 'silver mirror' forming on the inside of the boiling tube. 4. Add 2,4-DNPH (yellow solution) - makes a yellow/orange precipitate. Ketone 1. Add 2,4-DNPH (yellow solution) - makes a yellow/orange precipitate. Ketones do not give positive results with Fehling's solution, or Tollen's reagent. 272

NES/Chemistry/AS Carboxylic Acid 1. Add sodium carbonate, or sodium hydrogencarbonate - effervescence and CO2 gas made. 2. Add metal - effervescence and H2 gas made. Carboxylic acids (except methanoic acid and ethandioic acid) do not react with oxidising agents. 273

The Periodic Table of Elements Group 1 2 13 14 15 16 17 18 3 Key 1 9 2 Li 4 atomic number H 5 6 7 8 F He lithium Be atomic symbol hydrogen B C N O fluorine helium 6.9 beryllium name 1.0 boron carbon nitrogen oxygen 19.0 4.0 11 17 9.0 relative atomic mass 8 10.8 12.0 14.0 16.0 10 Na Cl 12 26 13 14 15 16 Ne sodium chlorine Mg Fe Al Si P S neon 23.0 35.5 19 magnesium 3 4 5 6 7 iron 9 10 11 12 aluminium silicon phosphorus sulfur 35 20.2 K 24.3 55.8 27.0 28.1 31.0 32.1 Br 18 44 potassium 20 21 22 23 24 25 27 28 29 30 31 32 33 34 bromine Ar Ru 39.1 Ca Sc Ti V Cr Mn Co Ni Cu Zn Ga Ge As Se 79.9 argon 37 ruthenium 53 calcium scandium titanium vanadium chromium manganese cobalt nickel copper zinc gallium germanium arsenic selenium 39.9 Rb 101.1 I 40.1 45.0 47.9 50.9 52.0 54.9 76 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 36 rubidium iodine 38 39 40 41 42 43 Os 45 46 47 48 49 50 51 52 Kr 85.5 126.9 55 Sr Y Zr Nb Mo Tc osmium Rh Pd Ag Cd In Sn Sb Te 85 krypton Cs strontium yttrium zirconium niobium molybdenum technetium 190.2 rhodium palladium silver cadmium indium tin antimony tellurium At 83.8 108 caesium 87.6 88.9 91.2 92.9 95.9 – 102.9 106.4 107.9 112.4 114.8 116.7 121.8 127.6 astatine 54 Hs 132.9 56 57–71 72 73 74 75 77 78 79 80 81 82 83 84 – Xe 87 hassium Ba lanthanoids Hf Ta W Re Ir Pt Au Hg Tl Pb Bi Po xenon Fr – barium hafnium tantalum tungsten rhenium iridium platinum gold mercury thallium lead bismuth polonium 131.3 francium 137.3 178.5 180.9 183.8 186.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 – 86 – Rn radon – 88 89–103 104 105 106 107 109 110 111 112 114 116 Ra actinoids Rf Db Sg Bh Mt Ds Rg Cr Fl Lv radium rutherfordium dubnium seaborgium bohrium meitnerium darmstadtium roentgenium copernicium flerovium livermorium – – – – – –––– – – lanthanoids 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 actinoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium 138.9 140.1 140.9 144.4 – 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.1 175.0 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium – 232.0 231.0 238.0 – – – – – – – – – – –