Question

Three test tubes $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$ are taken with ${\mathrm{CuSO}}_4$, ${\mathrm{FeSO}}_4$ and ${\mathrm{AgNO}}_3$ solutions respectively. What are the observations if:

a. $\mathrm{Fe}$metal is added to ${\mathrm{CuSO}}_4$ solution in the test tube $\mathrm{A}$?

b. $\mathrm{Cu}$ turnings are added to ${\mathrm{FeSO}}_4$ solution in the test tube $\mathrm{B}$?

c. $\mathrm{Zn}$ is added to ${\mathrm{AgNO}}_3$ solution in the test tube $\mathrm{C}$?

Answer 1

Displacement reaction: Reaction in which one of the higher reactive element displaces a less reactive element from its solution. $\mathrm{A}+\mathrm{BC}\to \mathrm{AC}+\mathrm{B}$ ( Here A is more reactive than B)

Reactivity series:

$\mathrm{K}>\mathrm{Na}>\mathrm{Ca}>\mathrm{Mg}>\mathrm{Al}>\mathrm{Zn}>\mathrm{Mn}>\mathrm{Fe}>\mathrm{Ni}>\mathrm{Sn}>\mathrm{Pb}>\mathrm{H}>\mathrm{Cu}>\mathrm{Hg}>\mathrm{Ag}>\mathrm{Au}>\mathrm{Pt}$

Here $\mathrm{K}$(potassium) is a highly reactive metal and $\mathrm{Pt}$(platinum) is the least reactive metal.

On the basis of the reactivity series, we can decide reaction will take place or not.

Three test tubes $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$ are taken with ${\mathrm{CuSO}}_4$, ${\mathrm{FeSO}}_4$ and ${\mathrm{AgNO}}_3$ solutions respectively.

a. $\mathrm{Fe}$metal is added to ${\mathrm{CuSO}}_4$ solution in the test tube $\mathrm{A}$.

Observation:

When iron metal is dipped in ${\mathrm{CuSO}}_4$ solution, displacement reaction takes place and formation of ferrous sulphate occur which is a green colour solution and on the iron deposition of copper takes place which turns grey colour iron to brown in colour.

Reaction

$\mathrm{CuSO}{}_4(\mathrm{aq})+\mathrm{Fe}(\mathrm{s})\to \mathrm{FeSO}{}_4(\mathrm{aq})+\mathrm{Cu}\left(\mathrm{s}\right)$

Copper(II)sulphate Iron Iron sulphate Copper

(Blue ) (Grey) (Green) (Brown)

Since $\mathrm{Fe}$ is more reactive than $\mathrm{Cu}$ displacement takes place.

b. $\mathrm{Cu}$ turnings are added to ${\mathrm{FeSO}}_4$ solution in the test tube $\mathrm{B}$.

Observation:

When copper metal is dipped in ${\mathrm{FeSO}}_4$ solution, a displacement reaction will not take place. Since $\mathrm{Cu}$ is less reactive than $\mathrm{Fe}$ so it cannot displace $\mathrm{Fe}$ from ${\mathrm{FeSO}}_4$ solution.

Reaction

$\mathrm{FeSO}{}_4(\mathrm{aq})+\mathrm{Cu}(\mathrm{s})\to \mathrm{no}\mathrm{reaction}$

Iron(II)sulphate Copper

Since $\mathrm{Fe}$ is more reactive than $\mathrm{Cu}$ displacement will not take place.

c. $\mathrm{Zn}$ is added to ${\mathrm{AgNO}}_3$ solution in the test tube $\mathrm{C}$

Observation:

When zinc metal is dipped in ${\mathrm{AgNO}}_3$ solution, displacement reaction takes place and formation of zinc nitrate occur which is colourless and formation of grey colour silver takes place.

Reaction

$2{\mathrm{AgNO}}_3\left(\mathrm{aq}\right)+\mathrm{Zn}\left(\mathrm{s}\right)\to \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+2\mathrm{Ag}\left(\mathrm{s}\right)$

Silver nitrate Zinc Zinc nitrate Silver

(Colourless ) (Grey) (Colourless) (Grey)

Since $\mathrm{Zn}$ is more reactive than $\mathrm{Ag}$ displacement takes place.