Question

White sticky substance formed when soap is mixed with hard water is called ____________.

Answer 1

Hard water

• Water that does not give lather with soap is called hard water.
• The presence of salts of Calcium$\left(\mathrm{Ca}\right)$ and Magnesium$\left(\mathrm{Mg}\right)$ is the reason behind its hardness.

When we use soap with hard water, it forms insoluble solid substances which are known as scum.

This is because Calcium ions ${\left(\mathrm{Ca}\right)}^{+2}$and Magnesium ions${\left(Mg\right)}^{+2}$ present in the hard water react with soap to form an insoluble substance Scum on clothes.

So, the white sticky substance formed when soap is mixed with hard water is called scum.