AQA A LEVEL CHEMISTRY PAPER 3 EXAM 2026 (Actual Exam) Questions with verified Answers (Latest Update 2026) UPDATE!! A+!!!

AQA A LEVEL CHEMISTRY PAPER 3 EXAM 2026 (Actual Exam) Questions with verified Answers (Latest Update 2026) UPDATE!! A+!!! (1) Make Up a Volumetric Solution - ANSWER 1. Weigh dry weighing boat 2. Place mass of solid into the boat and weigh accurately 3. Pour solid into a beaker. Reweigh empty weighing boat and calculate how much was transferred 4. Add deionised water and stir with glass rod until dissolved 5. Funnel into a volumetric flask 6. Make up to mark with deionised water until bottom of meniscus is on the mark 7. Stopper and invert to mix (2) Acid-Base Titration - ANSWER 1. Fill a burette 2. Use a pipette to transfer 25cm³ of the other solution into the conical flask 3. Add 2-3 drops of indicator 4. Start adding from the burette, swirling constantly, until the indicator changes colour. Record how much solution was added (rough titre) 5. Repeat to get concordant results and calculate a mean titre (3) Measuring Enthalpy Change of Combustion - ANSWER 1. Measure 100cm³ of water into a calorimeter 2. Weigh the spirit burner 3. Measure initial temperature of the water 4. Clamp calorimeter above spirit burner 5. Light the spirit burner 6. Heat until the temperature rises by 15°C. Stir and record final temperature 7. Reweigh spirit burner 8. Calculate temperature change and heat energy change (q=mcAT) 9. Calculate mass of fuel used and moles of fuel used. Calculate energy change per mole. (4) Measuring Enthalpy Change of Neutralisation - ANSWER 1. Place polystyrene cup in glass beaker 2. Measure out 25cm³ of 1moldm³ HCl and transfer to polystyrene cup 3. Stir and record temperature 4. Measure out 25cm³ of 1moldm³ NaOH into another measuring cylinder. 5. Add NaOH to HCl, stir and record the highest temperature reached 6. Calculate temperature change and q=mcAT 7. Calculate moles of acid used and water formed, and the enthalpy of neutralisation (5) Investigating Effect of Temperature on Rate of Reaction - ANSWER 1. Measure out 50cm³ of aqueous solution A and pour into a clean dry 250cm³ conical flask 2. Measure out 5cm³ of aqueous solution B and pour into test tube 3. Place conical flask on a piece of laminated paper with a cross. Add the acid and start the stopwatch 4. Gently stir and record initial temperature 5. Watch over the top and time how long it takes for the precipitate to form and cross to disappear 6. Note the final temperature and calculate the initial and final temperatures e.g sodium thiosulfate and acid: Na2S2O3 + 2HCl -- S + SO2 + H2O + 2NaCl (6) Preparing an Organic Liquid - ANSWER Heat under reflux. Most organic liquids are flammable = water bath. (7) Anti-Bumping Granules - ANSWER Small, rough pieces of silica that are added to the mixture before reflux. They provide a rough surface on which small gas bubbles can grow, avoiding bumping. They promote smooth, even boiling. (8) Separating a Crude Product - ANSWER Distillation apparatus. (9) Solvent Extraction (Purifying Product) - ANSWER 1. Place organic liquid in separating funnel and add a portion of aqueous solution 2. Stopper + shake, releasing the pressure by inverting and opening the tap 3. Allow separating funnel to stand until layers settle and separate 4. Remove stopper and open tap to run off bottom layer into a beaker. Close the tap partially to slow the flow towards the end. Run the second layer into a separate beaker. 5. Discard aqueous layer 6. Place organic layer back into funnel and repeat (10) Drying an Organic Liquid - ANSWER 1. Add a spatula of drying liquid (e.g. anhydrous CaCl2 or MgSO4) to the organic liquid 2. Swirl 3. Add more of the drying agent until the liquid changes from cloudy to clear 4. Filter or decant off the liquid into a clean, dry flask (11) Measuring Rates: Continuous Monitoring - ANSWER 1. Set up gas syringe attached to conical flask 2. Measure 50cm³ of HCl + add to flask 3. Add a 6cm strip of magnesium ribbon to the conical flask, place the bung firmly onto the top and start the timer 4. Record volume of hydrogen in the syringe every 15 seconds for 2.5 minutes 5. Repeat at different concentrations (12) Measuring Rates: Initial Rates - ANSWER 1. Fill burette with potassium iodide 2. Transfer 10cm³ of hydrogen peroxide into a 100cm³ beaker 3. Add 25cm³ to a 250cm³ beaker 4. Add 20cm³ deionised water into the beaker 5. Add 1cm³ of starch solution 6. Add 5cm³ potassium iodide from the burette 7. Add 10cm³ sodium thiosulfate solution 8. Add the hydrogen peroxide and start the timer 9. Stir 10. Stop the timer when the solution turns blue black 11. Repeat using different volumes of water and potassium iodide H2O2 + 2H+ + 2I- -- I2 + 2H2O (13) Measuring EMF of an Electrochemical Cell - ANSWER 1. Construct the electrochemical cell. First, clean the electrodes with emery before use. 2. Place one electrode into a 100 cm3 beaker with about 50 cm3 of 1 mol dm-3 (electrode) solution. 3. Place the other electrode into a 100 cm3 beaker with about 50 cm3 of 1 mol dm-3 (electrode) solution. 4. Use a strip of filter paper soaked in saturated potassium nitrate solution for the salt bridge 5. Connect the half cells by connecting the metals using the crocodile clips and leads provided to the voltmeter 6. Record measured voltage 7. Set up another cell using new solutions and a new salt bridge 8. Record voltage How pH Changes When A Weak Acid Reacts With A Strong Base - ANSWER 1. Rinse pH probe thoroughly with deionised water and shake gently. Place it in the standard pH 7 buffer solution to calibrate. 2. Fill burette with 0.1M NaOH solution 3. Use pipette to transfer excactly 20cm³ of 0.1M ethanoic acid to a clean 100cm³ beaker 4. Rinse pH probe with deionised water and clamp it into the ethanoic acid solution in the beaker. Stir gently with a rod and record the pH 5. Add the NaOH from the burette in 2cm³ intervals, stirring and measuring the pH after each interval until 18cm³ is added 6. Add NaOH in 0.2cm³ intervals until 22cm³ is added, recording pH after each interval 7. Add NaOH in 2cm³ intervals until 40cm³ is added 8. Plot pH (y) against volume of NaOH added (x) 9. Repeat with a strong acid and strong base Preparing an Organic Solid - ANSWER 1. Put a few anti-bumping granules in a 50cm³ pear shaped flask 2. In a fume cupboard, add 10cm³ ethanol, 12cm³ glacial ethanoic acid and 15 drops of conc sulphuric acid to the flask 3. Place a 250cm³ beaker with water on a tripod and gauze over a Bunsen burner 4. Clamp pear shaped flask in the beaker of water so the reaction mixture is below the water line 5. Add condenser and set up for reflux 6. Bring water bath to a gentle boil and continue for 15 mins. Turn off the bunsen and cool the mixture by removing the water bath. 7. Solid is separated by suction filtration Recrystallisation (Pure Organic Solids) - ANSWER 1. Dissolve impure crystals in minimum of hot solvent to ensure crystals form on cooling 2. Filter hot solution by gravity filtration, using a hot funnel and fluted filter paper to remove solid impurities 3. Allow solution to cool + crystallise. It might help to scratch the glass 4. Filter off crystals using suction filtration 5. Wash with ice cold solvent to remove aqueous impurities 6. Dry with air in a Buchner flask and place in low temperature oven Checking Purity Of An Organic Solid - ANSWER 1. Place some solid in a melting point tube sealed at one end 2. Place in m.p. apparatus and heat slowly 3. Record the melting temperature and the temperature when it stops melting 4. Repeat and average the remperatures 5. Compare m.p. to data book values M.p. range of + or - 2°C = pure What makes a good recrystallisation solvent? - ANSWER Dissolves the compound when hot, not when cold; impurities either soluble when cold or insoluble always. What steps are involved in recrystallisation? - ANSWER Dissolve in hot solvent, filter if needed, cool slowly to crystallise, filter off crystals, dry them. How can purity of the solid be assessed in recrystallisation? - ANSWER Measure melting point and compare with literature value; pure compounds have sharp melting ranges. Why might yield be low in recrystallisation? - ANSWER Product remains dissolved in solvent or lost during transfer. What safety precautions are important in distillation? - ANSWER Use anti-bumping granules, avoid sealing apparatus, heat gently, collect correct fraction. How is the purity of the liquid checked in distillation? - ANSWER Measure boiling point and compare to literature value. What drying agents are used and how? - ANSWER Anhydrous MgSO₄ or CaCl₂ - add until mixture goes from cloudy to clear. What can cause impurities in the distilled product? - ANSWER Incomplete separation, boiling over, poor drying. How do you test for alkenes? - ANSWER Add bromine water - orange to colourless. How do you test for alcohols? - ANSWER Add acidified potassium dichromate - orange to green if primary or secondary alcohol. How do you test for aldehydes? - ANSWER Tollens' reagent (silver mirror) or Fehling's (brick-red ppt). How do you test for carboxylic acids? - ANSWER Add sodium carbonate - effervescence due to CO₂. Why is it important to use a water bath when testing organic liquids? - ANSWER Many are flammable; heating directly with a flame is dangerous. What ligands tend to form linear complexes? - ANSWER Copper, silver and gold What type of isomerism can square planar complexes exhibit? - ANSWER cis-trans isomerism What does cisplatin look like? - ANSWER What does transplatin look like? - ANSWER Formula for Tollens' reagent and what does it test for? - ANSWER (Tests for aldehydes and forms a silver mirror) what type of isomerism is cis-trans isomerism - ANSWER Stereoisomerism What type of isomerism can octahedral molecules with three bidentate ligands show? - ANSWER Optical isomerism factors affecting shape of ligand - ANSWER -central metal ion present -ligands In the presence of ligands, what happens to electrons? - ANSWER The orbitals will split. Some of them gain energy, and some of them lose energy. What is delta E in transition metals? - ANSWER The difference in energy of the excited state and the ground state of the electron What happens if an electron absorbs energy equal to the energy gap of delta E? - ANSWER it can move to occupy the higher energy orbitals. This is called an excited electronic state. What is the formula for delta E - ANSWER What do these stand for in the formula delta E=hv or delta E = (hc)/λ - ANSWER ν is the frequency of light in hertz h is planck's constant c is the speed of light in ms-1 λ is the wavelength of the light in metres What affects delta E in transition metals? - ANSWER -the metal ion -its oxidation state -its ligands -its coordination number. What happens to a d-sub shell metal when there are no ligands present? - ANSWER NO d sub-shell splitting factors affecting the colour of transition metal ions: - ANSWER ligands and their geometries what happens when a transition metal ion is in light? - ANSWER it will absorb the frequencies which correspond to the d sub-shell energy gap Why does Fe(III) often appear yellow or orange when concentrated? - ANSWER This is because hexaaqua iron(III) is quite acidic, and will lose protons to become Fe(H2O)5(OH-) (and this is yellow). If you're asked what colour hexaaqua iron(III) is, what colour should you say? (Despite the fact that hexaaqua iron (III) is yellow when concentrated) - ANSWER purple Features of spectroscopy (transition metals) - ANSWER 1- White light shines through a coloured filter to remove everything but that colour of light 2- This light then falls on a transition metal sample solution 3- The more light it absorbs, the higher the concentration of the solution The energy gap from the wavelength of absorbed light depends on: - ANSWER -The metal ion -The metal's oxidation state -The ligands surrounding the metal -The coordination number What do you need to form a calibration curve (transition metal Spectroscopy)? - ANSWER measure absorbances of known solutions what colour is {Cu(Cl)4}2+ - ANSWER yellow what colour is {V(H2O)6}2+ - ANSWER violet what colour is {V(H2O)6}3+ - ANSWER green what colour is {Cu(H2O)6}2+ - ANSWER deep blue What colour is {Co(H2O)6}2+ - ANSWER pink What colour is {Co(NH3)6}2+ - ANSWER straw-coloured Vanadium (V) colour - ANSWER Yellow (VO2)+ Vanadium (IV) colour - ANSWER blue (VO)2+ Vanadium (III) colour - ANSWER green (V)3+ Vanadium (II) colour - ANSWER violet (V)2+ When reducing vanadium; what colour does the solution become when turning from Vanadium (V) to Vanadium (IV) and why? - ANSWER The solution goes from yellow to green to blue. It turns green, because (Yellow + blue = green) What metal is used to reduce Vanadium? - ANSWER Zinc redox potential - ANSWER the tendency of a molecule to acquire electrons standard redox potentials are quoted relative to - ANSWER a standard hydrogen electrode under standard conditions. What can redox potentials depend on? - ANSWER Ligands or pH What conditions are needed to measure standard redox potentials? - ANSWER Standard redox potentials are measured in aqueous solution. What affect does changing the ligand have on redox potentials? - ANSWER Changing the ligands will alter the redox potential depending on the bond strength to the metal. What does a higher concentration of H+ mean for redox potentials usually? - ANSWER Usually, a higher concentration of H+ means a higher redox potential. What type of solution does zinc have to be in to reduce vanadium? - ANSWER Different ions of vanadium can be prepared by successive reduction with zinc in acid solution. What conditions do KMnO4 need to be in to be reduced - ANSWER in acidic conditions, so you need to add an excess of sulfuric acid. what colour does KMnO4 go when reduced? - ANSWER colourless What is concordant results? - ANSWER Concordant titrations are titrations that give the same result, no more than 0.10cm3 apart. How do catalysts work? - ANSWER They provide an alternative reaction pathway with a lower activation energy What is a homogenous catalyst? - ANSWER a catalyst in the same phase as the reactants Why does the enthalpy profile of a catalysed reaction have two peaks? - ANSWER First, the catalyst is either oxidised or reduced. Then, the reverse happens. Both of these steps have a lower activation energy than the uncatalysed reaction, so this pathway is faster. What is a heterogenous catalyst? - ANSWER A catalyst that is in a different phase from the reactants Autocatalysis - ANSWER a reaction in which a product is the catalyst. What reaction is Mn2+ the (auto)catalyst of? - ANSWER The reaction between [MnO4]- and [C2O4]2- (homogenous catalyst) How is Mn2+ catalytic in the reaction between [MnO4]- and [C2O4]2-? - ANSWER 1) Mn2+ is catalytic because it reacts with MnO4- to make Mn3+. 2)The Mn3+ then reacts with the C2O42- where the Mn2+ is regenerated Why does the rate of reaction increase over time with autocatalysis? - ANSWER The production of the catalyst outweighs the concentrations of the reactants decrease and so the rate increases. Why is the reaction between the peroxodisulfate ion and the iodide ion initially slow? - ANSWER This reaction has a high activation energy and is slow because both ions are negatively charged; they repel each other, so require a lot of energy to collide What is the peroxodisulfate ion? - ANSWER (S2O8)2- What reaction does Fe2+ catalyse? - ANSWER the reaction between the peroxodisulfate ion and the iodide ion What are the half equations of the Fe2+ catalyst reaction? - ANSWER all aqeous (therefore Fe2+ is a homogenous catalyst) What does the reaction between the peroxodisulfate ion and the iodide ion produce? - ANSWER Iodine and sulfate ions How does a heterogeneous catalyst work? - ANSWER Reactants adsorb to the active sites of the catalyst surface. They react. The products desorb. Why does increasing the surface of a catalyst increase the rate of reaction? - ANSWER As more reactants are able to adsorb to the catalyst's surface How are catalysts made more efficient? - ANSWER -a support medium is commonly coated by the metal so that less metal needs to be bought -Increasing the surface area by making it a powder What is catalyst poisoning? - ANSWER Unwanted impurities adsorb to the catalyst's active sites and do not desorb. This blocks the active sites on the catalyst's surface. How does catalyst poisoning decrease the rate of reaction? - ANSWER it reduces the number of available active sites. What is an example of a reaction that uses a heterogenous catalyst? - ANSWER The contact process which is used to produce sulfuric acid What are the half equations of the contact process? - ANSWER How is SO3 converted to sulfuric acid? - ANSWER By adding water What catalyses the contact process? - ANSWER V2O5 (solid) at 450C and one (or two) atm What type of catalyst does the haber process use? - ANSWER a heterogenous catalyst (finely divided iron catalyst) what does the iron catalyst in the haber process allow for? - ANSWER a higher yield at lower temperatures (the forward reaction is endothermic) Why is the iron catalyst in the haber process powdered? - ANSWER to increase the surface area What is the iron catalyst in the haber process poisoned by? - ANSWER Sulfur Where does the sulfur impurity of the haber process come from? - ANSWER The hydrogen gas is often produced from methane. It will contain some impurities, of which sulfur is one How do we counteract the low yield of ammonia the haber process? - ANSWER we recycle unreacted gas and run the process again What are the conditions for the haber process? - ANSWER 450°C, 200atm pressure, iron catalyst and takes place in a sealed vessel Why is there optical isomerism with metal complexes? - ANSWER due to restricted rotation of the ligands about the central metal ion What does it mean if the E cell is positive? - ANSWER The reaction is feasible What substances do halogenoalkanes react with in a substitution reaction? - ANSWER NH3, OH-, CN- nucleophile - ANSWER electron pair donor electrophile - ANSWER electron pair acceptor Haloalkane + hydroxide ion - ANSWER alcohol haloalkane + ammonia - ANSWER amine haloalkane + cyanide ions - ANSWER nitrile Which haloalkane is the least reactive and why? - ANSWER A flouroalkane as the C-F bond is the strongest so requires the most energy to overcome (highest Ea) how to promote an elimination reaction between a haloalkane and OH-? - ANSWER -Heat under reflux (hot) -Use ethanol instead of water as a solvent (ethanolic conditions as opposed to aqeous conditions) What are the four equations of Ozone depletion? - ANSWER Cl2 - 2Cl∙ Cl∙+O3 - ClO∙ + O2 ClO∙ + O3 - 2O2 + Cl∙ 2Cl∙ - Cl2 what are the safer alternatives to cfcs? - ANSWER hydrofluorocarbons (HFCs) and hydrocarbons. Why do branched alkanes have lower boiling points? - ANSWER The molecule has less surface contact with other molecules so there is less area upon which van der waal forces can act. What is the general formula of an alcohol? - ANSWER Cn H2n+1 OH Why is E/Z isomerism shown in some alkenes? - ANSWER due to restricted rotation around the C=C bond How do you determine priority in E/Z isomerism? - ANSWER The highest atomic number gets priority 1. Then the placement of the highest priority group on each side determines whether it's E or Z what is the functional group isomer of an ester? - ANSWER carboxylic acid What is the functional group isomer of an alcohol - ANSWER an ether What is the functional group isomer of an aldehyde? - ANSWER a ketone What is the functional group isomer of an alkene - ANSWER cycloalkane What key features of the constant k in the rate equation do we need to know? - ANSWER It's temperature dependent It has different units for different reactions. The larger the rate constant... - ANSWER the faster the reaction. Why is the rate determining step the slowest step? - ANSWER It is the slowest because it has the highest activation energy for a successful collision. If the order of a molecule in the rate equation is two, what does this tell us? - ANSWER that there are two of these molecules involved in the rate determining step As the activation energy rises what happens to the rate constant? - ANSWER As the activation energy rises, the rate constant gets smaller (so the rate is slower). As temperature rises what happens to the rate constant? - ANSWER As temperature rises, the rate constant gets larger, so the rate is faster What is the equation of the iodine clock reaction? - ANSWER H2O2 + 2I- + 2H+ → 2H2O + I2 How does the iodine clock reaction work? - ANSWER initially the sodium thiosulfate will react with any iodine formed and remove it from the solution. Once all the sodium thiosulfate is gone, any iodine formed will turn the solution black by reacting with the starch. What type of experimental method for rate of reaction is the iodine clock reaction? - ANSWER Initial rates method In continuous monitoring, we tend to measure: - ANSWER Change in quantity of a substance What is the other type of experimental method for rates of reaction? - ANSWER Continuous monitoring and we do this by taking measurements of rates at specific intervals (Tend to measure change in quality of a substance ie loss of mass) Uses of Kevlar - ANSWER bulletproof and used in body armour. What reagent is used to observe hydrolysis? - ANSWER Silver nitrate (AgNO₃) in ethanol - precipitates silver halide as the halide ion is released. What is the role of ethanol in the reaction mixture in hydrolysis of halogenoalkanes? - ANSWER Acts as a solvent to dissolve the halogenoalkane (which is insoluble in water). What order do halogenoalkanes hydrolyse in terms of speed? - ANSWER Iodoalkanes bromoalkanes chloroalkanes - due to bond enthalpy differences. What observations are made when investigating the rate of hydrolysis of halogenoalkanes? - ANSWER Time taken for precipitate (AgX) to appear: white (AgCl), cream (AgBr), yellow (AgI). What experimental variable might be changed when measuring EMF? - ANSWER Concentration of ions in half-cells or temperature. How do non-standard conditions affect EMF? - ANSWER Affects electrode potentials (Nernst equation); e.g., increased [Zn²⁺] makes Zn²⁺/Zn less negative. What precautions ensure accurate measurements in EMF? - ANSWER Use high-resistance voltmeter, clean electrodes, fresh solutions, and a salt bridge. Why might EMF differ from theoretical values? - ANSWER Non-standard conditions, incomplete ion migration, or electrode contamination. What equipment is used for investigating pH changes? - ANSWER pH meter or pH probe with data logger or manual readings. What do pH curves show? - ANSWER Sudden vertical change at equivalence point; curve shape varies depending on strength of acid/base. What is the best indicator for strong acid-strong base titration? - ANSWER Phenolphthalein or methyl orange (both have range within steep section). Why is calibration of the pH probe important? - ANSWER Ensures accurate pH values; usually done using buffer solutions of known pH (e.g., pH 4, 7, 10). How is Ka determined experimentally? - ANSWER Measure pH of a known concentration of weak acid, then apply: Ka = H⁺² / HA (assuming H⁺ ≈ A⁻) What is used to measure pH accurately? - ANSWER A calibrated pH probe or pH meter. What assumptions are made when calculating Ka of a weak acid? - ANSWER H⁺ ≈ A⁻; initial acid concentration ≈ HA at equilibrium (minimal dissociation). enthalpy of solution formula - ANSWER lattice enthalpy dissociation + enthalpy of hydration Factors affecting entropy - ANSWER Temperature Physical state number of moles Conditions for entropy - ANSWER 1atm pressure 298K formula for entropy - ANSWER products - reactants (includes big numbers) endothermic reaction graph (entropy) - ANSWER negative gradient (delta G vs T) exothermic reaction graph (entropy) - ANSWER positive gradient (delta G vs T) If a reaction is either endothermic or has a negative entropy... - ANSWER it will have a temperature dependence If you add an excess of ammonia to an aqeous transition metal... - ANSWER If you add an excess of ammonia, you can get a ligand exchange reaction. The ammonia can replace some of the water ligands and some of the hydroxide ligands. This happens for the reaction with [Cu(H2O)6]2+ M2+ reacts with a carbonate. What happens? M2+ being a transition metal - ANSWER MCO3 is produced M3+ reacts with a carbonate. What happens? M3+ being a transition metal - ANSWER They release H+ ions which react with the carbonate ions: CO32-(aq) + 2H+(aq) → H2O(l) + CO2(g) if there is an excess of ammonia what happens? - ANSWER if there is an excess of ammonia. This allows ligand substitution reaction to happen. Cu 2+ (aq) - ANSWER blue solution Cu 2+ with NaOH - ANSWER Blue precipitate Cu2+ with ammonia - ANSWER deeper blue cu 2+ with carbonate - ANSWER green-blue carbonate How can accuracy be improved when investigating Ka of a weak acid? - ANSWER Ensure probe is calibrated, use freshly prepared solutions, avoid contamination. How do you reduce percentage uncertainty in measurements? - ANSWER Use larger volumes/masses, more sensitive equipment, repeat readings. Distillation - ANSWER NB, oxidation: Dilute acid and less K2Cr2O7 than needed. 1. Heat liquid to boil and vaporise the most volatile component in the mixture. Anti-bumping granules are used. 2. The vapour passes up from the flask and down into the condenser, where it is cooled by cold water and ice, and condenses back to a liquid (the distillate) which is collected in the flask. 3. Any dissolved solids are left in solution because they have too high a boiling point to be distilled over . Reflux - ANSWER NB, oxidation: conc acid and excess K2Cr2O7. 1. A mixture of liquids is heated to boiling point for a prolonged time. 2. Vapour is formed which escapes from the liquid mixture, is changed back into liquid (condenses) and returned to the liquid mixture. 3. Any (ethanal) and (ethanol) that initially evaporates can then be oxidised i.e. heat, vapour, condense, oxidised Thin Layer Chromatography - ANSWER 1. Draw pencil line 1.5cm from bottom of TLC plate + place 2 pencil crosses on the line 2. Place a drop of the purified solid on a watch glass + dissolve in a few drops of solvent 3. Use a capillary tube to place a spot of the solvent on a pencil cross. Allow spot to dry and repeat 3-4 times, ensuring diameter is no more than 0.5cm. This gives a concentrated spot 4. Repeat for pure solid 5. Place solvent in beaker at depth of 1cm 6. Place TLC plate in beaker and cover with lid 7. Allow solvent to run up the plate until it has almost reached the top 8. Remove from beaker + mark the line of the solvent front with pencil 9. Place plate in a fume cupboard until all of the solvent has evaporated and the plate is dry 10. View colourless spot by UV light or with ninhydrin 11. Measure distance from pencil line to spot and from pencil line to solvent front. Calculate Rf values Extrapolation (Enthalpy Changes) - ANSWER 1. Measure 50g of water into polystyrene cup held in a beaker 2. Start stop clock and record temp of water every minute for 3 minutes 3. On minute 4, add the 5g solid and stir vigorously 4. Read temp of solution every min for 15 mins 5. Plot graph of temp vs time 6. Extrapolate temp readings back from min 15 to min 4 7. Draw best fit line to give mean start temp from min 1 to min 3 8. Calculate temperature change at minute 4 Key apparatus for preparation of a standard solution? - ANSWER Volumetric flask, pipette and filler, burette, conical flask, white tile. How do you ensure an accurate standard solution? - ANSWER Use a mass balance to weigh solute accurately, dissolve fully in deionised water, and rinse all equipment into the volumetric flask before making up to the line. Why is a white tile used in titrations? - ANSWER To help detect the colour change more clearly at the end point. What indicators are used in acid-base titrations and why? - ANSWER Phenolphthalein (pink in alkali, colourless in acid) or methyl orange (yellow in alkali, red in acid) - depending on strong/weak acid or base used. How do you ensure accurate titration results? - ANSWER Repeat until concordant titres (within 0.1 cm³), swirl the flask, add dropwise near end point, rinse burette tip. How is heat energy calculated? - ANSWER ∆Q = mc∆T Why might your result be less exothermic than expected when measuring enthalpy change? - ANSWER Heat loss to surroundings, incomplete combustion, evaporation of fuel or solution. How can calorimetry be improved? - ANSWER Use a lid, insulate the container, use a bomb calorimeter for combustion reactions. What are the main sources of error in calorimetry? - ANSWER Heat loss, inaccurate temperature readings, assuming solution has same heat capacity as water. What visual method is used in the thiosulfate reaction? - ANSWER Time how long it takes for a cross to disappear under the flask as sulfur precipitates. How does increasing concentration affect rate? - ANSWER Increases frequency of collisions, leading to a faster rate. What is a control variable in the thiosulfate experiment? - ANSWER Temperature, volume of solutions, same person judging the disappearance of the cross. Why is the reaction considered to have a subjective end point in sodium thiosulfate and HCl reaction? - ANSWER The disappearance of the cross depends on human judgment, which can vary. What test is used for sulfate ions? - ANSWER Add HCl and BaCl₂ - white precipitate of BaSO₄ forms. What test is used for halide ions? - ANSWER Add dilute then concentrated HNO₃ and AgNO₃ - Cl⁻ (white ppt), Br⁻ (cream), I⁻ (yellow). What test is used for carbonate ions? - ANSWER Add HCl - effervescence due to CO₂, which turns limewater cloudy. What test is used for ammonium ions? - ANSWER Add NaOH and warm - test gas with damp red litmus (turns blue due to NH₃). Why is nitric acid used instead of HCl in halide tests? - ANSWER HCl contains Cl⁻ ions which would interfere with the test. What standard conditions are used in electrochemical cells? - ANSWER 1.00 mol/dm³ solution, 298 K, 100 kPa pressure, and inert platinum electrode if needed. What is the salt bridge for and what is it made of? - ANSWER Allows ion flow to maintain electrical neutrality; made of filter paper soaked in KNO₃. Which direction do electrons flow in an electrochemical cell? - ANSWER From the more reactive metal (more negative E°) to the less reactive metal (more positive E°). What is a standard hydrogen electrode? - ANSWER Reference electrode with E° = 0 V, used for measuring standard electrode potentials. what colour is {Fe(H2O)6}2+ - ANSWER pale green Transition Metal definition - ANSWER D block elements that form at least one stable ion with a partially filled d orbital Classic elements which are not transition metals despite being D-Block elements - ANSWER Scandium and Zinc properties of transition metals which are NOT shared by other metals - ANSWER -multiple oxidation states -coloured ions in solution -great catalysts -form complexes with ligands ligand - ANSWER a molecule which forms a dative bond with a transition metal complex ion - ANSWER A transition metal ion bonded to one or more ligands by coordinate bonds co-ordination number - ANSWER The number of co-ordinate bonds formed to a central metal ion What is an example of incomplete ligand substitution? - ANSWER [Cu(NH3)6]2+ to [Cu(NH3)4(H2O)2]2+ why does the coordination number not change when substituting water for ammonia ? - ANSWER because they are of a similar size Why does incomplete ligand substitution usually occur? - ANSWER when substituting ligands of a different size Denticity - ANSWER the number of dative bonds that can be formed with a transition metal by one ligand bidentate - ANSWER When a ligand can form two co-ordinate bonds in a complex ion. monodentate (or unidentate) - ANSWER A ligand that can form one bond Multidentate - ANSWER A ligand that can form multiple bonds Chelate effect - ANSWER the ability of multidentate ligands to form more stable metal complexes than those formed by similar monodentate ligands Why is the chelate effect a largely entropic effect? - ANSWER As you the number of moles of molecules in the products of the reaction increase. This leads to a large increase in entropy and this brings the Gibbs free energy below zero for the change. Why is enthalpy change negligible in ligand substitution? - ANSWER The (dative) bonds being broken and made are the same strength, amount and type. Why is carbon monoxide toxic? - ANSWER CO can from a strong dative bond with haemoglobin. This is a stronger bond than that made with oxygen and so it replaces the oxygen attaching to the haemoglobin. This can starve the body of oxygen. Ligand exchange/substitution - ANSWER when one ligand in a complex ion is replaced by a different ligand What are the four main geometries for complex ions? - ANSWER Octahedral, Tetrahedral, Square planar, Linear Mechanism: nucleophilic addition - ANSWER Mechanism: nucleophilic substitution - ANSWER Purifying organic substances: Drying - ANSWER Close tap of separating funnel, pour in mixture and place stopper at top Invert to mix, allowed layers to settle and add water to determine aq layer (it will increase in volume) place conical flask under and remove stopper + open tap to remove bottom layer Drying agents: MgSO4, CaSO4 Mechanism: electrophilic addition - ANSWER Mechanism: electrophilic substitution - ANSWER Bronsted-Lowry base - ANSWER proton acceptor Bronsted-Lowry acid - ANSWER proton donor Amphoteric - ANSWER a substance that can act as both an acid and a base acid + metal - ANSWER acid + metal - salt + hydrogen e.g. 2H+ + Mg -- Mg2+ + H2 acid + carbonate - ANSWER acid + carbonate - salt + water + carbon dioxide e.g. 2H+ + CuCO3 -- Cu2+ + H2O + CO2 acid + base - ANSWER acid + base - salt + water base is solid metal oxide or hydroxide e.g. 2H+ + MgO -- Mg2+ + H2O Sorensen's pH scale - ANSWER pH = -log[H+] [H+] = 10^(-pH) - low value of [H+] = high pH value - high value of [H+] = low pH value Strong acid - ANSWER completely dissociates in a solution HA (aq) -- H+ + A- ∴ [H+] = [HA] Ka - ANSWER Ka = [H+][A-]/[HA] -changes with temp (values usually standardised at 298K) Larger Ka = eqm is further right = greater acid strength Weak acid - ANSWER partially dissociates in solution Ka for weak acids - ANSWER Ka=[H+]^2/[HA] Approximations: 1) [H+]eqm = [A-]eqm dissociation of H+ in water will be small so neglected approximation breaks down for very weak/dilute acids (pH6) 2)[HA]start [H+]eqmtherefore [HA]eqm = [HA]start dissociation of weak acids is small, conc. of acid is much greater than conc. of H+ ions at eqmnot justified for stronger weak/dilute acids (Ka 10^-2)) Strong base - ANSWER e.g. NaOH -- Na+ + OH- [OH-] = [NaOH] Weak base - ANSWER pOH = -log[OH-] [OH-] = 10^(-pOH) pH + pOH = 14 Methods for preparing weak acid buffer solutions - ANSWER 1) CH3COOH(aq) -- H+(aq) + CH3COO-(aq) CH3COONa(s) + aq -- CH3COO-(aq) + Na+(aq) 2) partial neutralisation of a weak acid Excess CH3COOH(aq) + NaOH(aq) -- CH3COONa(s) +H2O(l) How buffers work: Ha -- H+ + A- (reversible) - ANSWER Adding small amount of acid, H+ : H+ conc increases H+ reacts w/ conjugate base A- eqm shifts left reduces H+ conc, pH maintained Adding small amount of alkali, A- : OH- conc increases OH- reacts with H+ to form water HA dissociates to form more H+ ions eqm shifts right increases H+ conc, pH maintained pH titration curve - ANSWER Lattice enthalpy - ANSWER The standard enthalpy change when 1 mole of an ionic compound is formed from its constituent gaseous ions under standard conditions exothermic Na+(g) + Cl-(g) -- NaCl(s) Standard enthalpy change of atomisation - ANSWER The enthalpy change that takes place for the formation of 1 mole of gaseous atoms from the element in its standard state under standard conditions endothermic Na(s) -- Na(g) 1/2Cl2(g) -- Cl(g) First ionisation energy - ANSWER The energy required to remove 1 electron from each atom of 1 mole of gaseous atoms to make 1 mole of gaseous 1+ ions endothermic Mg(g) -- Mg+ + e- First electron affinity - ANSWER The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form 1 mole of gaseous 1- ions Cl(g) + e- -- Cl-(g) Born-haber cycle - ANSWER Enthalpy change of solution - ANSWER The enthalpy change when 1 mole of a solute is completely dissolved in a solvent under standard conditions NaCl(s) + aq -- Na+(aq) + Cl-(aq) Enthalpy change of hydration - ANSWER The enthalpy change when 1 mole of isolated gaseous ions is dissolved in water forming 1 mole of aq ions under standard conditions exothermic Born-harber cycle 2 - ANSWER Hess cycle - ANSWER A= solution B= lattice enthalpy C= hydration Amino acid - ANSWER COOH group is acidic, reacts w/ bases by donating H+ NH2 group is basic, reacts w/ acids by accepting H+ Creates zwitterion (has both COO- and NH3+) Amino acid + base(aq) - ANSWER Amino acid + base(aq) -- salt + water Amino acid + alcohol - ANSWER Amino acid + alcohol -- ester + water Amino acid + acid - ANSWER Amino acid + acid -- salt (+ion) Isoelectric point - ANSWER pH at which zwitterion is formed If amino acid added to solution w/ pH greater: amino acid acts as acid and loses proton lower: amino acid acts as base and gains proton What ligands tend to form octahedral complexes? - ANSWER water and ammonia What ligands tend to form tetrahedral complexes? - ANSWER Chloride What ligands tend to form square planar complexes? - ANSWER Nickel, Palladium, Platinum Uses of Nylon - ANSWER commonly used in textiles. Why are polymers strong? - ANSWER Polymers are bound by van der Waals forces. The intermolecular forces are strong as the molecules are huge so there are lots of van der Waals forces between them! What is an example of a straight chained addition polymer? - ANSWER polyethene What are the two types of addition polymers? - ANSWER Straight and branched Why are Addition polymers often unreactive? - ANSWER This is because if the monomers were reactive, we'd get lots of side reactions during polymerisation.Addition polymers are NOT very reactive because the carbon chain is saturated and the side chains are usually non-polar. When do you add an "e" between molecule names? - ANSWER When there's 2 constants next to each other, ie pentanEnitrile (this also occurs with numbers too) Hydration of alkenes - ANSWER An industrial process that can be used to produce alcohols. The alkene is reacted with steam in the presence of an acid catalyst. Hydration of ethene: H2C=CH2 + H2O → CH3CH2OH A large difference between experimental and calculated lattice enthalpy values are due to... - ANSWER relatively large degrees of covalent bonding. positive ions can be said to polarise negative ions, if they cause distortion of the charge cloud. They can pull electrons to one side of the ion. assumptions of the ionic model - ANSWER -completely ionically bonded -perfectly spherical -of even charge distribution Amount of substance equations - ANSWER mass = mr x moles mol = vol x conc vol(gas) = mol x 24 (dm) PV=nRT (pressure, Pa, volume, m3, moles, -, 8.314, temp, k) Empirical formula - ANSWER The simplest whole number ratio of atoms of each element in a compound Molecular formula - ANSWER The number and type of atoms of each element in a molecule Celsius to Kelvin - ANSWER K=C+273 % yield and atom economy - ANSWER % yield = (actual/ theoretical) x 100 atom economy = (desired products/all reactants) x 100 Oxidising agent - ANSWER it itself is reduced, causes another species to be oxidised Reducing agent - ANSWER it itself is oxidised, causes another species to be reduced Oxidation - ANSWER Loss of electrons, increased oxidation number Reduction - ANSWER Gain in electrons, decreased oxidation number Balancing half equations - ANSWER Balance all atoms apart from oxygen and hydrogen Add H2O to balance oxygen Add H+ to balance hydrogen Add e- to balance charges Potassium manganate and iron ions [or (COOH)2] titrations - ANSWER Potassium manganate reduced (burette) Iron solution + excess dilute H2SO4 (provides H+ ions) added to conical flask (colourless) doesnt need indicator (self indicating) end point = permanent pink colour Fe2+ -- Fe3+ + e- MnO4- + 8H+ + 5e- -- Mn2+ + 4H2O MnO4- + 8H+ + 5Fe2+ -- Mn2+ + 4H2O + 4Fe3+ Iodine and sodium thiosulfate titrations - ANSWER Na2S2O3 oxidised (burette) oxidisng agent + excess KI produces iodine in conical flask (yellow-brown) titration -- pale straw colour add starch indicator (end point= blue-black -- colourless) I2 + 2e- -- 2I- 2S2O3 2- -- S4O6 2- + 2e- 2S2O3 2- + I2 -- S4O6 2- + 2I- ClO- content in bleach - ANSWER ClO- reacts w/ I- and H+ to form I2, then titrated Cu2+ content in copper (II) compounds - ANSWER For copper (II) salts, dissolve in water to form Cu2+ ions For insoluble copper (II) compounds, react w/ acid acid to form Cu2+ For copper alloys (e.g. brass or bronze), dissolve in conc. nitric acid then neutralise to form Cu2+ Cu2+ + I- -- I2 + CuI (overall brown coloured mixture) Voltaic cell - ANSWER Converts chemical energy to electrical energy Made by connecting 2 different half cells, allowing electrons to flow DONT MIX OR HEAT ENERGY MADE Half cell - ANSWER Contain species present in redox half-equation Metal/metal ion half cells - ANSWER Equilibrium set up at phase boundary where metal is in contact w/ its aq ion Forwards reaction shows reduction, reverse shows oxidation In isolated half cell, theres no net transfer of electrons into or out of cell Zn2+ (aq) | Zn (s) Cu2+ (aq) | Cu (s) Ion/ion half cell - ANSWER Ions of the same element in different oxidations tates Inert metal electrode used (Pt) Fe3+ (aq) + e- -- Fe2+ (reversible) Relative tendency - ANSWER Negative electrode= more reactive, loses electrons (oxidised) Positive electrode= less reactive, gains electrons (reduced) Standard electrode potential - ANSWER The tendency to be reduced and gain electrons Use half cell w/ H2 (g) and H+ solution w/ Pt electrode Standard electrode potential (E°) definition - ANSWER the emf of a half cell compared with a standard hydrogen half cell under standard conditions (298K, 1 moldm-3, 100kPa) Measuring E° - ANSWER electrode of half cell connected to standard hydrogen electrode by wire to allow connected flow of electrons two solutions are connected w/ salt bridge that allows ions to flow more neg E° value= greater tendency to lose electrons + undergo oxidation more pos E° value= greater tendency to gain electrons + undergo reduction Salt bridge - ANSWER Soak piece of filter paper in aq solution of KNO3 or NH4NO4 Contains conc. solution of an electrolyte that doesnt react w/ either solution Measuring standard cell potentials - ANSWER Prepare two standard half cells under standard conditions (for ion/ion half cells, have same conc) Connect to voltmeter using wires Prepare salt bridge + connect to solutions Record standard cell potential from voltmeter ELECTRONS FLOW FROM MORE NEG TO LESS NEG HALF CELL E° cell= E° (positive electrode) - E°(negative electrode) Predictions from electrode potentials - ANSWER Strongest reducing agent= most negative + most likely to be oxidised Strongest oxidising. agent= most positive + most likely to be reduced when writing over equations, keep red equation same way round + oxidation one reversed Limitations of predictions - ANSWER Reactions can have very high a.e so very slow reaction rates Value of electrode potential differ from standard value if conc isnt 1moldm-3 If conc 1 eqm shifts left, more electrons in system, E more neg If conc1 eqm shifts right, removes electrons, E less neg Conditions may not be standard, affects E value e.g. if not aq Storage cells - ANSWER cells/batteries require 2 electrodes w/ different electrode potentials Primary cells: non-rechargeable electrical energy produced by ox/red at electrodes used for low current long-storage devices (e.g. clocks, smoke detectors) most are alkaline based on Zn/MnO2 Secondary cells: rechargeable cell reaction can be reversed during re-charging so chemicals regenerated e.g. lead-acid (cars), Li ion/Li ion polymer (laptops, phones) Li ion/Li ion polymer - ANSWER Pros: low density, electrode is light + very reactive can be regular shape or solid flexible polymer + made into many shapes cons: toxic if ingested rapid discharge of current can cause fire hard to recycle as so reactive unstable at high temps Li+ moves between electrodes, electrons move through wires Positive electrode= metal oxide Neg electrode= graphite coated w/ Li metal Fuel cells - ANSWER Uses energy from reaction of fuel (e.g. hydrogen) w/ oxygen to create voltage Fuel and oxygen flow into fuel cell and products flow out, electrolyte remains in cell Can operate continuously provided fuel and oxygen are supplied into cell Dont have to be recharged Hydrogen fuel cells - ANSWER Can have alkali or acid electrolyte Cons: H2 is flammable gas w/ low bp (hard and dangerous to store and transport, expensive) Fuel cells have limited lifetime + use toxic chemicals Dynamic equilibrium - ANSWER Rate of forwards and backwards are equal and must be constantly occuring Conc of reactants and products doesnt change For system to remain in eqm, you need a closed system (temp, pressure and conc of reactants and products unaffected by surrounding) Le Chaterlier's Principle A + B -- C + D (reversible) - ANSWER When system is subject to change in conditions, position of eqm shifts to lessen effect of change Changes in conc: More of A added = shifts right, conc A decreases, creates more products Changes in temp: increase temp= favours endo (△H pos) Decrease temp= favours exo (△H neg) Changes in pressure: increase pressure= shifts side w/ fewer moles Catalyst= doesn't change eqm position (speeds up reaction, reaches eqm faster) Bond fissions - ANSWER Homolytic fission= each bonding atom receives one electron from the bonded pair, forming two radicals Radical= atom or groups w/ an unpaired electron Heterolytic fission= one bonding atom receives both electrons from bonded pair, this becomes negative ion and other becomes positive Alkane -- haloalkane - ANSWER Free radical substitution, halogen, uv light Haloalkane -- alkene - ANSWER NaOH, ethanol, reflux, elimination Alkene -- alkane - ANSWER H2, Ni catalyst, 150 degrees, hydrogenation, electrophilic addition Haloalkane -- nitrile - ANSWER NaCN or KCN, ethanol, reflux, nucleophilic substitution Haloalkane -- primary amine - ANSWER Ethanol (prevents sub. of H2O to form alcohol), excess NH3 (prevents further sub. of amine to form 2 + 3 amines), NaOH Primary amine -- secondary amine - ANSWER haloalkane, heat, nucleophilic substitution Secondary amine -- tertiary amine - ANSWER haloalkane, heat, nucleophilic substitution Alcohol -- haloalkane - ANSWER NaX, H2SO4, room temp, nucleophilic substitution Alcohol -- Ketone - ANSWER K2Cr2O7, H2SO4, reflux (secondary alcohol), complete oxidation Ketone -- alcohol - ANSWER NaBH4, warmed, reduction, nucleophilic addition Alkene -- alcohol - ANSWER H2O (steam)/H3PO4, hydration, electrophilic addition Alcohol -- alkene - ANSWER hot conc. H2SO4, reflux, dehydration Alcohol -- aldehyde - ANSWER K2Cr2O7, H2SO4, distillation (primary alcohol), partial oxidation Aldehyde -- alcohol - ANSWER NaBH4, warmed, reduction, nucleophilic addition Ketone -- hydroxynitrile - ANSWER NaCN/H+ Nitrile/Hydroxynitrile -- carboxylic acid - ANSWER dilute HCl, reflux, hydrolysis Aldehyde -- carboxylic acid - ANSWER K2Cr2O7, H2SO4, reflux, complete oxidation Alcohol -- carboxylic acid - ANSWER K2Cr2O7, H2SO4, reflux, complete oxidation Alcohol -- ester - ANSWER Carboxylic acid, acid catalyst, heat or Acyl chloride or Acid anhydride Ester -- alcohol - ANSWER Dilute acid/alkali, reflux, hydrolysis Ester -- carboxylate - ANSWER OH- (if NaOH used, salt formed), heat, alkaline hydrolysis Carboxylic acid -- ester - ANSWER alcohol, dilute aq acid catalyst, reflux, acid hydrolysis Ester -- carboxylic acid - ANSWER dilute aq acid, heat, acid hydrolysis Carboxylic acid -- acyl chloride - ANSWER SoCl2, substitution Acyl chloride -- carboxylic acid - ANSWER H2O, nucleophilic addition-elimination Acyl chloride -- ester - ANSWER alcohol, room temp, nucleophilic addition/elimination Acyl chloride -- 1 amide - ANSWER NH3, nucleophilic substitution Acyl chloride -- 2 amide - ANSWER 1 amine Carboxylic acid -- acid anhydride - ANSWER carboxylic acid/Heat Nitrile -- amine - ANSWER H2, high temp, high pressure, nickel catalyst, reduction Test for ammonium (NH4 +) - ANSWER Dilute NaOH + gently heat may be able to smell ammonia moist pH indicator -- blue NH4 +(aq) + OH-(aq) -- NH3(g) + H2O(l) Test for Carbonate (CO3 2-) - ANSWER Dilute acid Effervescence Gas (CO2) turns limewater milky CO3 2-(aq) + 2H+(aq) -- CO2(g) + H2O(l) Test for sulphate (SO4 2-) - ANSWER Dilute HCl + Barium chloride white precipitate (barium sulfate) formed Ba2+(aq) + SO4 2-(aq) -- BaSO4(s) Test for halides - ANSWER Dilute nitric acid + silver nitrate AgCl= white -- + dilute NH3= dissolves AgBr= cream -- dilute NH3= nothing -- conc. NH3= dissolves AgI= yellow -- conc. NH3= nothing Identifying organic compounds - ANSWER Alkene: mix with bromine water (orange -- colourless) COOH: sodium hydrogen carbonate (effervescence of CO2) or litmus paper (blue -- red) Aldehyde: tollens (silver mirror) Alcohol: acidified K2Cr2O7 (orange-- green for 1 and 2 alcs) Carbonyl: 2,4 DNPH (orange precipitate) Distillation - ANSWER Used to purify liquid Water in at lowest point Reflux - ANSWER Boiling a liquid w/ upright condenser Filtration under reduced pressure (separates solid from solvent) - ANSWER Connect one end of pressure tubing to filter pump, and other to Buchner flask, and turn on tap Place filter paper in Buchner funnel (connected to Buchner flask) and wet with some solvent used in preparing solid Pour mixture from beaker to centre of filter paper Rinse beaker with solvent Recrystallisation (purify solid) - ANSWER Pour solvent into conical flask Tip impure sample into second conical flask Add minimum hot solvent to impure sample Once dissolved, allow to cool, crystals form in conical flask Filter under reduced pressure to obtain dry crystalline solid Melting point determination (Identifies purity of product) - ANSWER Add ~3cm depth of product to melting point capillary, tap on table to shake to bottom Place in sample hole + thermo. in thermometer hole of melting point apparatus Use rapid heating setting, observe through magnifying window Observe m.p when solid melts Repeat w/ lower temp so more accurate