Question

How to write a net ionic equation for reaction between potassium hydroxide and calcium carbonate?

Answer 1

The chemical formula of potassium hydroxide is $KOH$and that of calcium carbonate is $CaC{{O}_{3}}$. In the question we are asked to write the complete reaction between them. Such types of reactions come under the category of the double displacement reaction.

Complete step-by-step answer: Let us firstly understand what does we mean by the double displacement reaction.
The reactions in which two compounds react to form two other compounds by the mutual exchange of atoms or groups of atoms are called double displacement reactions.
The reaction as per the question can be written in ionic form as represented below.
We know that $CaC{{O}_{3}}$and $KOH$ both are the ionic compounds and when dissolved in water, then they dissociate into their corresponding ions.
Dissociation of the ionic compound $CaC{{O}_{3}}$can be written as follow;
$CaC{{O}_{3}}\left( aq \right)\to C{{a}^{2+}}\left( aq \right)+CO_{3}^{2-}\left( aq \right)$
Now, dissociation of potassium hydroxide can be written as follows;
$KOH\left( aq \right)\to {{K}^{+}}+O{{H}^{^{-}}}$
Now, when we intermix both the compounds in the solution, then the calcium ions pair up with the hydroxide ions and potassium ion pair with the carbonate ion.
But we need to take care of one thing that we know that calcium ion has +2 charge and hydroxide ion $\left( O{{H}^{-}} \right)$have only one negative charge. So, to balance the charge we will require two $\left( O{{H}^{-}} \right)$ions.
Similarly, $CO_{3}^{2-}$have two negative charges so in order to balance the charge we will require two ${{K}^{+}}$ions.
Hence the net reaction can be written as
$\left( 2{{K}^{+}}+2O{{H}^{-}} \right)+\left( C{{a}^{2+}}+CO_{3}^{2-} \right)\to \left( 2{{K}^{+}}+CO_{3}^{2-} \right)+\left( C{{a}^{2+}}+2O{{H}^{-}} \right)$
Hence the net reaction can be written as,
$CaC{{O}_{3}}+2KOH\to {{K}_{2}}C{{O}_{3}}+Ca{{\left( OH \right)}_{2}}$
We should note that potassium ion being more reactive than the calcium ion displaced the calcium ion from the calcium carbonate (salt solution).

Note: We should note that in double displacement reaction always a metal of higher reactivity displaces a metal of the lower reactivity from its salt solutions. To know which metal is more reactive than another, we have a series termed as reactivity series which needs to be followed. Few trends of the reactivity series are as follows.
$K>Na>Ba>Ca>Mg>Al>Zn>Fe>Co>Ni>Sn>Pb>H>Cu>Ag$