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ANSWERS: Displacement2019EvidenceAchievementMeritExcellence1. (a) (i)(ii)2. (i)(ii)DisplacementFe + Pb(NO3)2 → Fe(NO3)2 + PbA. copper sulfate B. iron sulfate C. zinc sulfate D. magnesium sulfateThe reactions occurring are displacement reactions.Reactions occur in the wells where a more reactive metal (higher on the activity series) will displace a less reactive metal (lower on the activity series) ion from the solution. The more reactive metals will transfer electrons to the metal ions during the displacement reactions.In the spotting tiles with zinc metal and copper sulfate, and zinc metal with iron sulfate, displacement reactions occur because zinc metal is more reactive (higher on the activity series) than copper and iron metal, so it displaces the copper and iron ions in the solutions. This results in a (brownish) solid (copper) forming in the first well and fading of the blue copper sulfate solution to form a colourless zinc sulfate solution. In the second well, a silvery grey solid (iron) forms, and the pale green iron(II) sulfate solution becomes colourless.In the well with zinc metal and magnesium sulfate, no reaction occurs / no change seen because the magnesium ions are not displaced by the zinc metal since magnesium is more reactive than zinc.The zinc metal will not react with zinc sulfate because a metal ion will not displace the same metal – no change in the well.Correct? ALL solutions correct.? Describes displacementreactions (cannot just state displacement reactions).ORIdentifies reaction / no reaction in the spotting tiles with zinc metal.Gives symbol equation? Either:Explains displacementreaction with reference toactivity series.ORExplains displacementreaction with reference toelectron transfer.? Explains observations inTWO of the spotting tileswith zinc metal.? Elaborates on displacementreaction with reference to activity series and electron transfer AND explains the observations in all spotting tiles with zinc metal.2018EvidenceAchievementMeritExcellence(a)(b)(c)(i) circledMagnesium is higher on the activity series of metals than zinc. This means magnesium is more reactive than zinc. So, magnesium atoms will lose electrons to form magnesium ions more easily than zinc atoms loses electrons to form zinc ions.This is what is already present in the test tube, as magnesium nitrate contains magnesium ions and zinc metal contains zinc atoms.Therefore, no reaction occurs.(iii) circledInitially the solution is blue due to the Cu2+ ions in the solution.As zinc is more reactive than copper, zinc atoms donate electrons to go into the solution as zinc ions which are colourless. Copper ions accept the electrons to form copper metal.As the concentration of copper ions in the solution decreases, the blue colour of the solution fades and eventually disappears as they are replaced by colourless zinc ions.(ii) circledLead is higher in the activity series and is therefore more reactive than silver. Therefore, lead atoms lose electrons and go into the solution as lead ions. Silver ions gain electrons and form silver atoms, that is, silver metal. So, the new solid that is formed issilver.This is a displacement reaction. A more reactive metal displaces ions of a less reactive metal.Pb(s) + 2Ag+(aq) → Pb2+(aq) + 2Ag(s)(i) circled and magnesium is more reactive/higher on activity series than zinc or zinc is less reactive than magnesium.(iii) circled and blue colour of solution fades / goes colourless.(ii) circled and lead is more reactive than silver.Recognises displacement reaction in (b) or (c).(i) circled and magnesium is more reactive but is already magnesium ions / zinc is less reactive and is already zinc atoms / magnesium atoms will lose electrons more easily.(iii) circled and blue solution due to Cu2+ ions, colour gets lighter / colourless.Explains colour fading due to Cu2+ gaining electrons OR that Zn is more reactive than Cu, so Cu ions are removed(ii) circled and lead more reactive /silver less reactive and some reference to electron loss / gainDisplacement reaction explained and unbalanced equation correct.(i) circled with full explanation.OR(iii) circled and fullexplanation including Zn and Cu reactivity, electron transfer and colours of both Cu and Zn ions.(ii) circled and full explanation, including balanced equation and electron loss / gain forreactant to product, e.g. Pb loses electrons to form Pb2+2017EvidenceAchievementMeritExcellence(a)(i)Zinc + lead nitrate →?lead + zinc nitrate? BOTH correct word equations.Zinc chloride + lead nitrate →?zinc nitrate + lead chloride(ii)(b) The reaction between zinc metal and lead nitrate is classified as a displacement reaction because when zinc metal is placed into a solution of lead nitrate, the zinc metal displaces lead ions in solution to form zinc nitrate, since zinc is higher on the activity series. Zinc metal loses two electrons to form Zn2+ and the electrons are gained by Pb2+ to form Pb.When zinc chloride and lead nitrate solutions are mixed, a precipitation reaction (or exchange reaction) occurs rather than a displacement reaction. This is because when thetwo solutions (zinc chloride and lead nitrate) are added together, an insoluble precipitate forms.OR because when the two solutions are added together, ions from each substance are swapped or exchanged, and an insoluble substance (precipitate) forms.During displacement reactions, metals which are higher on the activity series will displace metal ions from solutions lower on the activity series. The more reactive metals will transfer electrons to the metal ion. A metal which is further down the activity series cannot displace metal ions from solutions higher on the activity series and so no reaction will occur.A > C > B (most to least reactive)Metal A displaces both B and C – so it must be the most reactive and be at the top of this activity series.? Describes a displacement reaction.? Identifies the precipitation reaction.? Correct order: ACB.? Explains precipitation referencing the specific reaction substances in (a) (ii). (Minor error allowed)? Explains a displacement reaction correctly with reference to EITHERatoms forming ions and ions in solution being displaced ORelectron transfer in the correctdirection, related to the equation in (a) (ii) OR the correct order in (b).(Minor error allowed.)? Explains precipitation fullyincluding, EITHERjustification of the precipitate usingthe rules of precipitationORrecognition of the spectator ions /soluble product.? Explains a displacement reaction correctly with reference to BOTH atoms forming ions and ions in solution being displacedAND electron transfer in the correct direction related to the equation in (a) (ii)OR the correct order in (b).2015EvidenceAchievementMeritExcellence(a)(i)Displacement reaction.Identifies the correct reaction type.(ii)When the orange / pink / brown solid (copper) is added to the colourless solution (silver nitrate), a grey solid (silver) forms, and the solution turns blue as copper nitrate solution is formed.Describes TWO observations.Links the observations to THREE of the reactants and products.(iii)Cu(s) + 2Ag+(aq) → 2Ag(s) + Cu2+(aq)Unbalanced equation. Correct balanced (ionic) equation. (b)If the metal is silver, the metal strip will remain silver-grey, and the copper sulfate solution will remain blue.If the metal is magnesium, then an orange / pink / brown solid will form (copper), and the blue copper sulfate solution will fade and form a colourless solution of magnesium sulfate. When magnesium is added to the copper sulfate solution, a displacement reaction occurs as magnesium is able to displace the copper from solution, as magnesium is higher than copper on the activity series / magnesium is more reactive than copper.A displacement reaction will not occur if the metal strip is silver, as copper is more reactive than silver / silver is not able to displace copper ions from solution.Describes correct observations for either metal.Identifies species formed.Describes a displacement reaction for silver and magnesium metals.Links observations to species for EITHER silver or magnesium.Links the identification of the metals through displacement to the activity series.Explains why there would be a reaction with magnesium AND why there would not be a reaction with silver, with observations fully linked to species for both metals. ................
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