EDEXCEL A LEVEL CHEMISTRY (PAPER 3) ACTUAL EXAM TEST QUESTIONS & ANSWERS (A+ GRADED 100% VERIFIED) 2025 LATEST!!

EDEXCEL A LEVEL CHEMISTRY (PAPER 3) ACTUAL EXAM TEST QUESTIONS & ANSWERS (A+ GRADED 100% VERIFIED) 2025 LATEST!! what can heat help a solid do? - ANSWER-dissolve why should the volumetric flask be shaken when making a standard solution? - ANSWER-to ensure a uniform concentration why is a volumetric pipette more accurate than a measuring cylinder? - ANSWER-smaller uncertainty if the burette isn't rinsed with the substance that will be put in it, residual water might have what effect? - ANSWER-dilute the concentration leading to a larger titre what is the problem with leaving the funnel in the burette? - ANSWER-small drops of liquid may fall from the funnel leading to a lower titre volume why is it okay to rinse with distilled water in a titration? - ANSWER-it doesn't add any extra mols of reagents what can you do to decrease apparatus uncertainties? - ANSWER-decrease sensitivity uncertainty by using a greater resolution or increase the size of the measurement how would you reduce % uncertainty in a burette? - ANSWER-make the titre a larger volume by increasing conc and vol of the substance in the conical flask or decreasing the conc of the substance in the burette 2 | Page how would you reduce % uncertainty in measuring mass? - ANSWER-use a balance that measures to more decimal places is water a poor or good nucleophile? - ANSWER-poor how does water react with halogenoalkanes - ANSWER-slowly in a substitution reaction why does water go in the liebig condenser from the bottom? - ANSWER-to go against gravity allowing more efficient cooling and preventing the backflow of water why should electric heaters be used to heat organic substances? - ANSWER-highly flammable why should a reflux condenser never be sealed? - ANSWER-build up of gas pressure could cause explosion what are anti-bumping granules? - ANSWER-prevent vigorous uneven boiling by making small bubbles form instead of larger bubbles general method for purifying an organic liquid - ANSWER-put distillate of impure product into a separating funnel, was by adding saturated NaCl, allow layers to separate then run off the aq layer, run the organic layer into a dry conical flask and add drying agent (eg anhydrous calcium chloride), carefully decant the liquid into the distillation flask, distill to collect pure product detailed method for preparing and purifying an ester - ANSWER-mix primary alcohol and carb acid, add conc sulphuric acid drop by drop (to prevent uncontrolled boiling) and cool in a water bath, when all acid has been added fit a reflux condenser to the flask and gently heat the mixture over an electric heating mantle, cool mixture and re-arrange apparatus for distillation, shake distillate in separating funnel with NaCO3 soln releasing the pressure at intervals, the lower aq layer is discarded, the crude ester is shaken in a separating funnel with 3 | Page CaCl soln removing any unreacted alcohol then discard the lower layer, the ester is run into a clean dry flask with anhydrous cacl, the ester is filtered into a clean dry flask with some anti bumping granules and distilled describe the steps in purifying an organic solid - ANSWER-dissolve the impure compound in a minimum vol of hot solvent, hot filter solution to remove any insoluble impurities, cool the filtered solution by inserting the beaker in ice, use buchner filtration to separate out crystals, wash the crystals with distilled water to remove soluble impurities, dry crystals between filter paper what in an advantage of steam distillation? - ANSWER-the product distills at a lower temperature which can prevent decomposition why should wire not be used in the salt bridge? - ANSWER-it will set up its own electrode system with the ions components of the SHE - ANSWER-0 volts E, Hydrogen gas at 100kpa, H+ ions at 1moldm3, 298k, pt black catalyst (porous an can absorbs hydrogen gas) Ecell - ANSWER-Ecell = Erhs-Elhs why a re high resistance voltmeters used? - ANSWER-to stop the current from flowing disadvantages of fuel cells - ANSWER-expensive, transporting pressurised liquid, limited lifetime, use of toxic chemicals in production how can hydrogen be stored in fuel cells? - ANSWER-liquid under pressure, adsorbed onto a solid surface, absorbed within a solid material