Would you be able to check if water is hard by using a detergent?
No, we would not be able to check if water is hard by using a detergent. Detergents remain effective in hard water and do not show any visible difference when used with hard or soft water.
The charged ends of detergents do not form insoluble precipitates with the calcium and magnesium ions present in hard water. Unlike soaps, which react with these ions to form a white curdy precipitate (scum) and produce less foam in hard water, detergents continue to form foam easily in both types of water.
Since detergents work similarly in both hard and soft water without forming any scum, they cannot distinguish between them. Soaps are better suited for detecting water hardness.
Explanation
The textbook explains that detergents are effective cleansing agents in hard water because their charged ends do not form insoluble precipitates with calcium and magnesium ions. Activity 4.12 demonstrates this difference - soap forms a curdy solid in hard water while detergent does not. Therefore, detergents cannot be used to detect water hardness since they behave identically in both hard and soft water, unlike soaps which clearly show visible differences (scum formation and reduced foaming) in hard water.