CAMBRIDGE IGCSETM CHEMISTRY:COURSEBOOKExam-style questions and sample answers have been written by the authors.In examinations,the way marks are awardedmay be different.Coursebook answersChapter 1Science in context:Lord of the ringsrises very quickly,the melting and boilingpoints are close together,the liquid stage1 Jupiter and Saturn are the biggest of theis not seen as it boils quicklyplanets in our solar system and are made ofbyou would need to heat the solid slowly sohydrogen and helium in the gaseous state.that the temperature rise is not too quick;There is a progression outwards from the Sunyou could use an electrical heater so youin terms of the structure of the planets.Thosecan control temperature more carefully;nearest the Sun are rocky and relatively small;you could use an oil bath to heat the solidbeyond Mars the planets are gaseous.and carefully control the temperature so it2 Hydrogen molecules are the smallest of allis kept between the melting point (114 C)the elements and therefore the forces betweenand boiling point(184 C)of iodinethem are very small.The gas needs to behighly compressed(so that the molecules areExperimental skills 1.1close together)and at a very low temperature(so that the molecules are moving slowly)in1 Substance B is a pure substance as the curve isflat while the substance melts.Substance A isorder for it to condense into a liquid.a mixture as there is no single melting point-Questionsthat region of the curve is sloped.2Take temperature readings at shorter time1 a freezingintervals (e.g.every 30s);use of a digitalb boilingthermometer would give more accuratereadings/use of a temperature sensor linkedcondensationto a computer would enable the readings to be2 ataken continuously and enable the graph to bemethaneplotted as the readings were being taken.Theb ethanol and mercury;they have meltingsamples can be re-heated and cooled again,points below room temperature,butallowing duplicate sets of data to be collected.boiling points above room temperaturec the impurity lowers the freezing point ofthe liquid3 aa volatile liquid is one that evaporateseasily;it has a low boiling pointb ethanol water ethanoic acid;ethanol is the most volatile,ethanoic acidis the least volatileB;both the melting point and boilingpoint are above room temperature;therefore,it is a solidCambridge IGCSETM Chemistry-Harwood,Millington Lodge Cambridge University Press 2021CAMBRIDGE IGCSETM CHEMISTRY:COURSEBOOKChapter 1 continuedQuestions10 In a the liquid levels are the same as there isair both inside and outside the porous potcylinder;in b hydrogen diffuses into the potfaster than air molecules diffuse out becausehydrogen molecules have less mass than the airmolecules;this produces an increase in pressureinside the pot and so the liquid level is pushedfreezingdown on the left (and up on the right).0solid20Exam-style questionsTime6 a Moving slowly [1];close to each other [1];6A solid;B=energy released;C=energy absorbed7A solid;B=liquid;C=liquid and gasc evaporation(vapour);D=gasd changing from liquid to solid;Experimental skills 1.27a evaporation of the liquid [1];anddiffusion of the gas particles[1];1 silver iodideb particles moved more slowly [1];because2 silver nitrate potassium iodidethe temperature was lower[1];silver iodide +potassium nitrate8aa solid [1];is cooling down [1];3 the rates of diffusion of silver and iodide ionsb they are moving more slowly [1];and4 because the rates of diffusion of the ions arecloser together[1];not the same-silver ions are less heavy and sodiffuse slightly more quicklyc heat comes from the formation of bonds(interactive forces)between the particles[1];Questions9aammonia,which is alkaline,reached theindicator first to change its colour [1];8 Evaporation of bromine takes place asbecause it moved faster [1];because itmolecules escape from the surface of thewas lighter [1];liquid,the gaseous bromine molecules thenspread throughout the gas jar to completelybC50s;fill the container,there are collisions withrate of diffusion is inversely related to theair molecules,bromine molecules movemolecular mass;heavier molecules,suchfrom a region of high concentration toas HCI here,diffuse more slowly thanlow concentration and so are completelylighter moleculesmixed with the air and at the sameconcentration throughout.Answers A and D are too short;answerB too long.Simple proportion would9 a Methylamine molecules have a greatersuggest about 73s,but the rate ofmass than ammonia molecules and sodiffusion is inversely related to the squarediffuse more slowly;the white smoke ringroot of the molecular mass.Ammoniawill be more central than for ammonia/molecules diffuse 1.46 times as fast ashydrogen chloride,slightly to the right ofhydrogen chloride molecules.;centre as methylamine diffuses slightlyfaster than hydrogen chloride.bhydrogen bromide(from hydrobromic acid)or hydrogen iodide(from hydroiodic acid)Cambridge IGCSETM Chemistry-Harwood,Millington Lodge Cambridge University Press 2021CAMBRIDGE IGCSETM CHEMISTRY:COURSEBOOKChapter 2Getting started4Protons are positively charged and wouldtherefore repel each other/the presence of the1 'H'andO'are the chemical symbols forneutrons counteracts this repulsion and meansa hydrogen atom and an oxygen atom,that the nucleus can hold together.respectively.Water consists of two hydrogenatoms chemically bonded to one oxygen atom.5BWhen atoms join together like this,they form621 protons and neutrons;protons anda molecule.A molecule must have more thanneutrons are both nucleonsone atom in it.7Chlorine-37 has two more neutrons in2You may have heard of protons,neutrons andthe nucleus.electrons;these are subatomic particles,andthey come together to make the many different8A nitrogen atom has 7 protons and 7 electronstypes of atom.and therefore is electrically neutral.All atomsare electrically neutral.Science in context:Seeing is believingWorked example 2.111 relative atomic mass of iridium is 192The rings are made up of carbon atoms(not many elements can form rings likeA,=(191×37.3)+(193×62.7)1100=192.3this);carbon is the basis of the moleculesAnswer corrected to three significant figures asof life because it can form so manythis is the accuracy of the data given.different structures.2That the proportions of the two isotopesThere are 19 atoms in all (count all theare 50:50(1:1)as the relative atomic mass iscorners);arranged in five hexagonal rings.exactly midway between the masses of thetwo isotopes.Experimental skills 2.1The metal present is responsible fordetermining the colour seen in the flame.The non-metal present is the same in all casesQuestionsand so cannot be responsible for the change.1proton =1,neutron=1,electron =02 It is a physical change.(or1/1840)3 It will be the salt which gave the bluest colour2 15 protons,16 neutrons,15 electronsflame.The results will depend on which salts3 An element is a substance that cannot beyou tested.broken down into anything simpler bychemical means.Atoms are the particles that make up allsubstances;they are the smallest particleof an element that shows the propertiesof that element;they can join together tomake molecules.Each element has its own type of atom-theatoms of an element all have the same numberof protons and electrons.Cambridge IGCSETM Chemistry-Harwood,Millington Lodge Cambridge University Press 2021