Doc Brown's Chemistry KS4 Science GCSE/IGCSE Chemistry Revision Notes

3. Metal Reactivity Series Experiments-Observations

What do you see? The observations of the reactivity series of metals reacting with water, metals reacting with hydrochloric acid and metal displacement reactions are described and tabulated below.

3a metal + water * 3b metal + acid * 3c metal + salt solution * 3d metal/carbon + solid oxide

More details like word/symbol equations are given in Part 1.

SEE ALSO 1. Reactivity Series of Metals * 2. RUSTING & Introducing REDOX reactions and ...

Metal Extraction Fe, Cu, Al etc.  *  Transition Metals  *  Other notes on using metals eg Al & Ti  *  Metal Structure - bonding

• All you need is a selection of metals, water, universal indicator, rack of test tubes and a splint.

• Ideally all the metals would be in the same physical state, other than all being solids, i.e. same sized granules or same sized sheet of same thickness. However this is isn't possible within a school laboratory (or its budget!).

• The experiment is extremely easy to do, simply add small similar sized portions of the metal to a few cm³ of cold water containing a few drops of universal indicator.

• Before adding the metal the indicator should give a green colour indicating neutral ~pH 7.

• Keep an eye on all of them at the same time and note any changes and the relative rate of evolution of gas bubbles.

3a. Results: Table of possible observations

Metal	Possible observations
aluminium turnings	no change - no reaction
calcium granules	Slow reaction, effervescence, colourless gas evolved. The universal indicator turns blue-purple - alkaline solution (pH ~13)
copper strip	no change - no reaction
iron filings	no change - no reaction
lead strip	no change - no reaction
lithium - pea sized lump!	Moderately fast reaction - effervescence, colourless gas formed  TEACHER DEMONSTRATION in large trough of water!  The universal indicator turns blue-purple - alkaline solution (pH ~13)
magnesium ribbon	Very slow reaction, bubbles slowly form on the surface of the magnesium ribbon. Around the magnesium ribbon the universal indicator turns pale blue - weakly alkaline solution (pH ~11)
potassium - pea sized lump!	Very fast reaction - effervescence, colourless gas formed  TEACHER DEMONSTRATION in large trough of water!  The universal indicator turns blue-purple - alkaline solution (pH ~13)
sodium - pea sized lump!	Fast reaction - effervescence, colourless gas formed, may ignite with a larger lump  TEACHER DEMONSTRATION in large trough of water!  The universal indicator turns blue-purple - alkaline solution (pH ~13)
tin strip	no change - no reaction
zinc granules	no change - no reaction

• No reaction = no observed change, in some cases where theoretically there should be a reaction, you might not see any change.

• If there is any reaction, bubbles of colourless gas will form.

• In this experiment you are judging the relative reactivity by observing how fast each metal appears to react with water.

• This is simply judged by the evolution of colourless gas bubbles of hydrogen, readily tested for using the calcium reaction - the colourless gas gives a 'pop'! with a lit splint - hydrogen.

• Any change in the indicator colour also indicates a chemical change is taking place.

• -

3a. Conclusions and comments.

• From the observations you can reasonably deduce the following reactivity order

  • potassium > sodium > lithium > calcium > magnesium

  • but the rest do not react, so all you can say is that they appear less reactive than magnesium.

• All the equations you need are on the page 1. The Reactivity Series of Metals, but some examples are given below

  • sodium + water ==> sodium hydroxide + hydrogen

  • 2Na(s) + 2H₂O(l) ==> 2NaOH(aq) + H_2(g)

  • and

  • calcium + water ==> calcium hydroxide + hydrogen

  • Ca(s) + 2H₂O(l) ==> Ca(OH)_2(aq/s) + H_2(g)

• Comments on some of uses of the metal relevant to these observations

  • This property makes it a useful metal for out-door purposes e.g. aluminium window frames, greenhouse frames.

  • Zinc is used in galvanising, i.e. coating iron or steel to prevent rusting. The zinc corrodes preferentially forming a protective oxide layer.

  • Tin's lack of reactivity enables it to be used as a protective layer in steel cans of fruit - tinned cans!

  • Lead's lack of reactivity has enabled it in the past to be used for water pipes, though it is being replaced by plastic tubing or piping for two reasons - (i) lead is a toxic metal and plastic is cheaper!

  • Copper can be used for roofing, where it corrodes superficially, and very slowly, to give a green protective layer of a basic carbonate (its a mixture of insoluble hydroxide and carbonate).

• -

3b. The Reaction of Metals with Hydrochloric Acid

• All you need is a selection of metals, dilute hydrochloric acids, rack of test tubes and a splint.

• Ideally all the metals would be in the same physical state, other than all being solids, i.e. same sized granules or same sized sheet of same thickness. However this is isn't possible within a school laboratory (or its budget!).

• The experiment is extremely easy to do, simply add similar sized small portions of the metal to a few cm³ of cold dilute hydrochloric acid.

• Keep an eye on all of them at the same time and note any changes and the relative rate of evolution of gas bubbles.

3b. Results: Table of possible observations

• No reaction = no observed change, in some cases where theoretically there should be a reaction, you might not see any change.

• If there is any reaction, bubbles of colourless gas will form.

• In this experiment you are judging the relative reactivity by observing how fast each metal appears to react with the dilute hydrochloric acid.

• This is simply judged by the evolution of colourless gas bubbles of hydrogen, readily for tested using the magnesium reaction - the colourless gas gives a 'pop'! with a lit splint.

• Aluminium, again gives problems with the observations because of the oxide layer inhibiting the reaction with the salt solution of a less reactive metal.

• -

3b. Conclusions and comments.

• From the observations you can reasonably deduce the following reactivity order

  • calcium > magnesium > zinc > iron

  • but the rest hardly react, so all you can say is that they appear less reactive than iron.

• All the equations you need are on the page 1. The Reactivity Series of Metals, but some examples are given below

  • magnesium + hydrochloric acid ==> magnesium chloride + hydrogen
  • Mg(s) + 2HCl(aq) ==> MgCl_2(aq) + H_2(g)
  • zinc + hydrochloric acid ==> zinc chloride + hydrogen
  • Zn(s) + 2HCl(aq) ==> ZnCl_2(aq) + H_2(g)

• -

3c. Metal Displacement Reactions (metal + salt solution)

• All you need is a selection of metals, salt solutions of the same metals (eg. chloride, nitrate or sulphate) and rack of test tubes.

• The physical state of the metal in terms of granule size or area of sheet doesn't matter in this experiment.

• See also metal extraction experiments in section 3(d)

3c. Results: Table of possible observations

• No reaction = no observed change, in some cases where theoretically there should be a reaction, you might not see any change (see Al note below).

• Aluminium, again gives problems with the observations because of the oxide layer inhibiting the reaction with the salt solution of a less reactive metal.

• The displaced copper can display a variety of colours depending on how the precipitate-coating forms, and how much of it - I'm afraid that's the way it is!

• In some cases the metal crystals formed by the displacement reaction are very small and scatter the light so that they can look quite dark - almost black, rather than a silver-shiny precipitate.

3c. Conclusions and comments.

• Any colour change indicates a displacement reaction has occurred,

• AND the rule is that

• a more reactive metal will displace a less reactive metal from its salt solution (irrespective of which salt)

• Of the series of metals tested magnesium appears to be the most reactive because it displaces all the other metals being investigated here.

• Copper appears to be the least reactive in this limited series because it does not displace any of the other metals.

• Therefore by considering what will displace what from the results table, you can quite legitimately deduce that in terms of reactivity order

  • magnesium > aluminium > zinc > iron > lead > copper

  • BUT the observations for aluminium and lead may not show up clearly.

  • What you can definitely deduce in a more restricted experiment is the reactivity series order

  • magnesium > zinc > iron > copper

• Examples of displacement equations

• The first metal on the left is the most reactive, and the last metal on the right, is the displaced less reactive metal.

  • magnesium + copper sulphate ==> magnesium sulphate + copper
    • Mg(s) + CuSO_4(aq) ==> MgSO_4(aq) + Cu_(s)
    • The blue of the copper sulphate solution fades as colourless magnesium sulfate is formed.
  • zinc + copper sulphate ==> zinc sulphate + copper
    • Zn(s) + CuSO_4(aq) ==> ZnSO_4(aq) + Cu_(s)
  • aluminium + copper(II) sulphate ==> aluminium sulphate + copper
    • 2Al(s) + 3CuSO₄(aq) ==> Al₂(SO₄)₃(aq) + 3Cu(s)

• -

3d. Simple Metal Extraction Experiments  (with reducing agents)

• Heating oxides or carbonates with powdered charcoal (mainly carbon)
  • If you strongly heat copper(II) carbonate with finely powdered charcoal (mainly carbon) you can reddish-brown specks of copper in resulting mixture. The dark green copper(II) carbonate turns black initially as copper(II) oxide is formed, but this is then reduced to copper by the charcoal.
    • initially a thermal decomposition: CuCO₃ ==> CuO + CO₂
    • then the reduction reaction (O loss): 2CuO + C ==> 2Cu + CO₂
    • You can of course start the experiment with copper(II) oxide, but copper carbonate is closer to the sort of naturally occurring copper ore that is mined.
  • You can do a similar experiment by heating lead(II) oxide with powdered carbon and you can get silvery lead formed BUT in a fume cupboard please, since lead fumes are very poisonous!
    • 2PbO + C  ==> 2Pb + CO₂
    • Lead is a sufficiently unreactive metal for carbon to displace it.
  • If you heat iron oxides with powdered carbon nothing happens however strongly you heat the mixture in a test tube. Although carbon is reactive enough to displace iron, the temperature in the test tube isn't high enough - you need a blast furnace!
  • If you heat the white powder of aluminium oxide with carbon powder, nothing happens because carbon isn't 'reactive' enough to displace aluminium ie aluminium is too reactive forming very stable compounds.
• Metal displacement reactions with solid oxides plus reactive metal
  • Your teacher can demonstrate two metal extraction displacement reactions.
  • Neither are used commercially, but they do illustrate how chromium and titanium are extracted.
  • Both these reactions are very exothermic - lots of heat released
  • The Thermit Reaction
    • You ignite a mixture of brown iron(III) oxide and silvery grey aluminium powder using a magnesium fuse. The mixture goes off like a firework in a shower of sparks!
    • On examining the cold residue you find a lump of iron and specks of white aluminium oxide.
    • 2Al + Fe₂O₃ ==> Al₂O₃ + 2Fe
    • Aluminium is more reactive than iron and so will displace iron from iron compounds.
  • Heating a mixture of magnesium powder and copper(II) oxide
    • Silvery grey magnesium powder is mixed with black copper oxide powder and heated strongly in a test tube.
    • The mixture glows red hot and on examining the cold mixture you see specks of white magnesium oxide and reddish-brown specks of copper.
    • Mg + CuO ==> MgO + Cu
    • Magnesium is more reactive than copper and so will displace copper from copper compounds.
• See also Metal Displacement Reactions (metal + salt solution) section 3c

OTHER ASSOCIATED PAGE LINKS

SEE ALSO 2. RUSTING & Introducing REDOX reactions

and 3. Metal Reactivity Series Experiments-Observations

  Easy KS3 science multiple choice quiz start on metal reactivity and KS3 word-fills

and GCSE/IGCSE m/c QUIZZES on metal reactivity

Foundation-tier Level (easier) multiple choice quiz on the Reactivity Series of Metals

or Higher-tier Level (harder) multiple choice quiz on the Reactivity Series of Metals

and GCSE/IGCSE reactivity gap-fill worksheet or Rusting word-fill worksheet

KS4 Science GCSE/IGCSE/O level Chemistry revision notes pages:

The Periodic Table  *  Group 1 Alkali Metals  *  Methods of Metal extraction

Transition Metals  *  Alloys-uses of metals  *  Electrochemistry-Electrolysis

Rates of Reactions Experiments (e.g. metal-acid)

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