Cobalt Sulphate and Lead Nitrate combine to form Lead Sulphate. This happens because of _______.

Always evaluate the solubility of various chemicals to forecast the reaction's direction, since this may help us rapidly determine the reaction's flow. Every response strives to keep its reaction quotient constant (Q).

The Sulphate mentioned in the question, i.e., Cobalt Sulphate CoSO₄ is a soluble sulphate. It reacts with nitrate, Lead Nitrate $\left(\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\right)$ and forms Lead Sulphate $\left({\mathrm{PbSO}}_4\right)$, which is an insoluble sulphate.

The reaction is represented as:

$\mathrm{CoSO}4\left(\mathrm{aq}\right) + \mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2 \left(\mathrm{aq}\right) \to \mathrm{Co}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right) + {\mathrm{PbSO}}_4\left(\mathrm{s}\right)$

The ionic reaction for this chemical reaction will be as follows:

${\mathrm{Pb}}^{2+}+ {\mathrm{SO}}_4^{2-}\to {\mathrm{PbSO}}_4 \left(\mathrm{s}\right)$

We see that in this case, a double displacement reaction is occurring. 

In this reaction, ionic reactions are taking place and the cations and anions are interchanging their places with each other to form completely new substances. 

Since the product substance ${\mathrm{PbSO}}_4$ is insoluble sulphate it forms a white precipitate at the bottom of the container.