One sample of tap water contains dissolved ions such as Ca²⁺(aq), Mg²⁺(aq), and CO₃^2-(aq). A 150.-gram sample of this tap water contains 0.000 75 gram of CaCO₃(aq). When these ions in the tap water are present in greater concentrations, the water is called hard water. The hard water can damage water pipes and water heaters by producing large deposits of solid calcium carbonate, known as scale. Some homeowners have a water softener to replace positive ions, such as Ca²⁺(aq) and Mg²⁺(aq), in hard water with sodium ions, Na⁺(aq).

71 Determine the parts per million of CaCO3 in the tap water sample. [1] . Answer--> 5ppm...no work 0.000 75g/150.g    x 1,000,000 72 State, in terms of aqueous ions, why this tap water can conduct an electric current. [1 Answer-->charge can move 73 Using the key in your answer booklet,, draw at least 2 water molecules in the box, showing the orientation of each water molecule toward the Ca2+ ion. [1]   Answer-->