Displacement Reactions

Question 1

what is a displacement reaction

Answer 1

a reaction in which one element replaces another element in a compound

Question 2

what are displacement reactions called in organic chemistry

Answer 2

substitution reactions

Question 3

what would a reaction between Mg(s) and CuSO4(aq) produce

Answer 3

Cu(s) + MgSO4(aq)

Question 4

what would a reaction between 2Al(s) and Fe2O3(s) produce

Answer 4

2Fe(s) + Al2O3(s)

Question 5

what are the two things both of of those reactions have in common in terms of the reactants and products

Answer 5

• they both have a metal reacting with a compound of a different metal
• they produce a metal and a different metal compound

Question 6

what two things do the reactions have in common in terms of the type of reaction

Answer 6

• they are displacement reactions
• as a more reactive metal on the reactants side has taken the place of a less reactive metal in a compound
• and they are redox reactions

Question 7

what is the difference between the two reactions in term of their states

Answer 7

• the first reaction involves the interaction of a solid and compound in an aqueous state (in an aqueous solution)
• whereas the all the reactants and products in the second one are solids

Question 8

what do these reactions taking place in different states imply about the differences in the energy required in order for a reaction to occur in the first place

Answer 8

• the first reaction takes place without any energy needing to be inputted
• whereas the second one requires a lot of energy to be supplied for a high temperature

Question 9

where are these two reactions likely to take place

Answer 9

• the first one is likely done in a lab

- whereas the second one is likely done for a specific purpose in industry

Question 10

what colour changes would occur if you added magnesium to copper sulfate solution

Answer 10

• the blue colour of the solution becomes paler
• if an excess of Mg is added the solution would become completely colourless
• the solid Mg changes colour from silvery to brown

Question 11

why does the blue colour of the solution become paler as you add Mg

Answer 11

• the Mg is displacing the Cu from the CuSO4 solution
• leading to its concentration decreasing
• and therefore the strength of its colour in the solution decreasing or fading

Question 12

why does the solution become colourless if an excess of Mg is added

Answer 12

• excess means all the Mg that can react with sulfate ions has reacted
• meaning that all the Cu from CuSO4 has been displaced
• this leads to the solution losing all its blue colour as no CuSO4 is present
• making it colourless (as MgSO4 is colourless)

Question 13

why does the solid Mg change its appearance from silvery to brown

Answer 13

• the solid copper forming forms a layer on the surface of the solid Mg
• causing the Mg (visible to the eye) to go brown

Question 14

what is the ionic equation and net ionic equation for the reaction between magnesium and copper sulfate

Answer 14

• Mg(s) + Cu(2+)(aq) + SO4(2-)(aq) = Cu(s) + Mg(2+)(aq) + SO4(2-)(aq)
• Mg(s) + Cu(2+)(aq) = Cu(s) + Mg(2+)(aq)

Question 15

why does this net ionic equation show that this is a redox reaction

Answer 15

• the Mg atoms give two electrons to the Cu2+ ions
• meaning the Mg atoms are oxidised as they lose electrons (OIL)
• and the Cu2+ ions are reduced as they gain electrons (RIG)
• oxidation + reduction = redox

Question 16

what is the reaction between aluminium and iron(III) oxide used for practically

Answer 16

joining reals together by railway industries

Question 17

why isnt it effective to join rails together by welding them

Answer 17

• the metals are good conductors of heat

- so its very hard to get the two ends of the rail hot enough for them to melt and join together

Question 18

what is the thermite method that is used instead

Answer 18

• a mixture of aluminium and iron oxide is is put above the place where the two rails are to be joined
• a Mg fuse is lit causing the Al + Fe3O3 reaction to occur

Question 19

what happens after the Mg fuse is lit

Answer 19

• the reaction is so exothermic that the iron if formed as a molten metal
• which is then poured in the gap between the two rails
• after cooling the rails r joined together

Question 20

what is the ionic equation and net ionic equation for the reaction between Al and Fe3O3

Answer 20

• Al(l) + 2Fe(3+)(l) + 3O(2-)(l) = 2Fe(l) + 2Al(3+)(l) + 3O(2-)(l)
• 2Al(l) + 2Fe(3+)(l) = 2Fe(l) + 2Al(3+)(l)