Reactivity Series Worked ExamplesIGCSE Chemistry 0620

(a) Potassium is at the top of the reactivity series, so the reaction is very vigorous. Observations: it floats, moves around on the surface, fizzes, melts into a ball, burns with a lilac flame and disappears. Any three.

(b) Calcium is lower than potassium, so it reacts steadily rather than violently: bubbles (fizzing), the calcium sinks and gradually disappears, and the water turns cloudy (white) because calcium hydroxide is only slightly soluble. Any two.

(c) A reactive metal and water give a metal hydroxide and hydrogen.

(d) The gas is hydrogen: a lighted splint gives a (squeaky) pop.

The more reactive the metal, the faster it reacts with acid and the more bubbles of hydrogen appear. The order of the four metals is magnesium > zinc > iron > copper.

(a) W (most bubbles): magnesium. X: zinc. Y (few bubbles): iron. Z (no bubbles): copper.

Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid — there is no reaction.

(b) Metal + hydrochloric acid → salt (a chloride) + hydrogen.

A metal displaces another metal from a solution of its ions only if it is more reactive. Count the ticks for each metal: P 3, R at least 1, S 1, Q 0.

R cannot displace P, so P > R. S does not react with R nitrate, so R > S. S displaces Q, so S > Q. (a) Order: P > R > S > Q.

(b) R is more reactive than S (S could not displace R), so R will displace S from S nitrate: ✓ (reaction).

(c) P. In each displacement, the metal added loses electrons and becomes an ion while the metal ion in solution gains electrons. P displaces all the others, so P forms positive ions most readily.

X displaces iron, so X is more reactive than iron: it loses electrons to form positive ions more readily than iron does. Answer: B.

A is wrong: X does not displace zinc, so X is less reactive than zinc. C reverses the result — iron is less reactive than X, so iron cannot displace X.

D is wrong: X is above iron, and iron is above copper, so X would displace copper from copper(II) sulfate.

(a) Only zinc with iron(II) sulfate reacts: zinc is more reactive than iron, so it displaces iron. Silver is less reactive than zinc, so it cannot displace zinc — no reaction.

(b) A grey/black solid (iron) forms on the zinc, and the pale green solution becomes colourless (zinc sulfate is colourless).

(c) Sulfate ions are spectator ions and are left out.

(d) Zinc atoms are oxidised: each loses two electrons to become a $\text{Zn}^{2+}$ ion ($\text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^-$). The $\text{Fe}^{2+}$ ions gain these electrons and are reduced.

(a) Each small division is $1\;^{\circ}\text{C}$, so read to the nearest half division ($0.5\;^{\circ}\text{C}$) and record every value to one decimal place: magnesium $43.5\;^{\circ}\text{C}$, zinc $30.5\;^{\circ}\text{C}$, iron $26.0\;^{\circ}\text{C}$.

Temperature change = highest temperature − starting temperature.

(b) The displacement reactions are exothermic, and the further apart two metals are in the series, the more energy is released. Largest rise = most reactive: magnesium > zinc > iron.

(c) Copper cannot displace itself — copper added to copper(II) sulfate gives no reaction, so there is no temperature change to compare.

(d) Use an insulated (polystyrene) cup with a lid instead of a boiling tube, so that less heat is lost to the surroundings and the measured rise is closer to the true value.

(a) To remove the layer of magnesium oxide from the surface, so that the steam can reach the magnesium itself.

(b) The mineral wool holds the water so it does not run along the tube; heating it produces steam. Heat under the magnesium strongly, and heat the mineral wool gently from time to time to keep steam flowing.

(c) Magnesium reacts with steam to form magnesium oxide (not the hydroxide) and hydrogen.

(d) The first gas that bubbles out is mainly the air that was already in the apparatus, pushed out ahead of the hydrogen.

(e) As the tube cools, the gas inside contracts and water would be sucked back into the hot tube, which could crack it.

(a) At $6$ min read up to each curve: aluminium $38$ cm³, iron $34$ cm³ (each small square is $2$ cm³).

(b) Iron produces hydrogen straight away. The aluminium line stays flat at zero (almost no gas) for about the first $3$ minutes.

(c) Aluminium is covered by a thin, unreactive layer of aluminium oxide that stops the acid reaching the metal, so at first there is almost no reaction.

The acid slowly removes the oxide layer. Once the aluminium itself is exposed, it reacts faster than iron (its line becomes steeper than iron's), because aluminium is more reactive.

A reacts rapidly with cold water — most reactive. D reacts only very slowly with water but rapidly with acid. B reacts slowly with acid. C does not react with acid at all.

(a) Order: A > D > B > C.

(b) C — it does not react with dilute acid, so it is below hydrogen, and its oxide is reduced by carbon; copper fits both results.

(c) B's oxide is reduced by carbon, so B is below carbon. D's oxide is not reduced, so D is above carbon (D would have to be extracted by electrolysis).

(d) A reacts rapidly even with cold water, so its reaction with acid would be dangerously violent.

(a)(i) Manganese is above zinc, and zinc is above copper, so manganese is more reactive than copper: it reacts, displacing copper.

(a)(ii) Magnesium is above aluminium, so manganese is less reactive than magnesium: no reaction.

(b) The blue solution fades (becomes paler/colourless) and a red-brown (pink-brown) solid of copper forms. Manganese atoms lose electrons; copper(II) ions gain them.

(c) Manganese is above hydrogen, so it gives a salt and hydrogen. With $\text{Mn}^{2+}$ and $\text{Cl}^-$ the salt is $\text{MnCl}_2$.

(a) Zinc forms $\text{Zn}^{2+}$ and silver ions are $\text{Ag}^+$, so two silver ions are needed to take the two electrons lost by one zinc atom.

(b) Moles of zinc, then use the 1 : 2 ratio.

Mass of silver:

(c) The strip loses the zinc that reacted and gains the silver deposited.

(d) The silver ion, $\text{Ag}^+$, is the oxidising agent: it gains electrons (is reduced) and so oxidises the zinc.

(a) Untreated aluminium is covered by a thin, unreactive oxide layer that stops the copper(II) ions reaching the metal.

(b) Each Al atom loses 3 electrons; each $\text{Cu}^{2+}$ ion gains 2. The lowest common multiple is 6, so 2 Al atoms give 6 electrons to 3 $\text{Cu}^{2+}$ ions.

Check the charge: left $3 \times (2+) = 6+$; right $2 \times (3+) = 6+$. ✓

(c) Moles of aluminium, then the 2 : 3 ratio.

Mass of copper:

(d) Moles of $\text{Cu}^{2+}$ needed = $0.0300$ mol. Volume = moles ÷ concentration, then convert dm³ to cm³.