Reactivity Series And Displacement Reactions (T2)

Question 0

Describe what happens when chlorine is added to sodium bromide solution…

Answer 0

When chlorine is added to sodium bromide solution, the bromine is DISPLACED by the chlorine.

The solution turns brown, and the brown colour is the displaced bromine.

The chlorine has gone to form sodium chloride.

The Cl and Br have swapped places.

Chlorine + sodium bromide -> sodium chloride + bromine
Cl2(aq) + 2NaBr(aq) -> 2NaCl(aq) + Br2(aq)

Question 1

Briefly describe the reactivity series..

Answer 1

• many elements, particularly metals, react with acids to make salts
• a “reactivity series” is established by determining which metal is more reactive and putting the metals in order of that reactivity
• the elements at the top of the series will act with the most chemicals, even water
• as we move down the elements become less reactive
• this ordering is done by establishing a displacement reaction

Question 2

In which group on the periodic table does a displacement reaction happen every time? Explain…

Answer 2

A displacement reaction happens with all of the halogens.

A more reactive halogen displaces a less reactive halogen from a solution of one of its salts

The most react reactive halogen displaces all of the other halogens from solutions of their salts, but is itself displaced by none of the others.

Vice versa for the least reactive.

Question 3

If an element is more ….. than the other element in an …… compound, it will effectively shove the ……. …….. out of the way and become part of the compound.

Element + compound -> ……… + ……….

Answer 3

If an element is more reactive than the other element in an aqueous compound, it will effectively shove the less reactive out of the way and become part of the compound.

Element + compound -> compound + element

Question 4

List the elements in the reactivity series from most reactive to least reactive, with the following columns…

Element Ion Reacts with

Answer 4

Element Ion Reacts with

Potassium       K+        Water
Sodium           Na+      Water
Lithium            Li+        Water
Calcium           Ca2+    Water
Magnesium     Mg2+   Acids
Aluminium       Al+       Acids
Carbon            C+        Acids
Zinc                 Zn2+     Acids
Iron                  Fe2+     Acids
Hydrogen        H+        
Copper            Cu2+    Strong acids
Silver               Ag+       Strong acids
Gold                Au+       Strong acids

Question 5

Hydrogen and carbon are not metals but still often included in the reactivity series. Why and how?

Answer 5

Hydrogen and carbon are not metals but they can displaces another elements as if they were, so are often included.

This happens through oxidation and reduction; the loss (oxidation) or gaining of electrons (reduction)

Question 6

Some elements in the reactivity series are so reactive they will happily react with water. Give the chemical equations for sodium reacting with water…

Answer 6

Sodium + water -> sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)

Question 7

Iron requires acids to react. Give the chemical and word equations for iron reacting with sulphuric acid..

Answer 7

Iron + sulphuric acid -> iron sulphate + hydrogen

Fe(s) + H2SO4(aq) -> FeSO4(aq) + H2(g)

Question 8

Substances at the top of the reactivity series are more likely to LOSE electrons and become oxidised than those further down, which require a stronger and stronger stimulus to oxidise.

So, substances tend to replace less reactive chemicals and as with the movement of ions this can happen with electrons as well as entire atoms.

Show, with word and chemical equations, what happens when magnesium and zinc react with hydrogen ions…

Answer 8

Magnesium + hydrogen ions -> hydrogen and magnesium ions
Mg(s) + 2H+(aq) -> H2(g) + Mg2+(aq)

Zinc + hydrogen ions -> hydrogen + zinc ions
Zn(s) + 2H+(aq) -> H2(g) + Zn2+(aq)

Mg and Zn both react with hydrogen ions and can ‘reduce’ the hydrogen ions into normal hydrogen atoms while they become ‘oxidised’ by gaining the positive charge.

This shows both Mg and Zn are more reactive than hydrogen.

Question 9

What happens if we react magnesium with zinc ions?

Answer 9

Magnesium + zinc ion -> zinc + magnesium ion
Mg(s) + Zn2+(aq) -> Zn(s) + Mg2+(aq)

The Mg is more reactive than Zn and therefore ‘reduces’ the Zn, oxidising itself with the electrons.

Question 10

Describe how displacement reactions can be used to extract certain metals from aqueous solutions..

Answer 10

If copper salts are exposed to iron, the iron will displace the copper, extracting the copper from the aqueous solution as a solid.

If you put iron nails in copper sulphate, the copper (which gives the liquid its blue colour) is being replaced with iron which forms as a powder and may plate the nails being used.

Question 11

Describe a very crude way of determining the position of an element in the reactivity series..

Answer 11

By observing the speed at which the element reacts with a very weak acid.

Rust is when iron reacts with water and oxygen, over a long period of time.

Iron is very low on the reactivity series so we can assume that if it reacts with water, most of the elements will react with weak or strong acid, just at very different rates.

The rate and force of the reaction can be used as a crude means of determining the position in the reactivity table.