Seawater contains dissolved salts in the form of ions. Some of the ions found in seawater are Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-, HCO₃^-, and SO₄ ^2-. An investigation was conducted to determine the concentration of dissolved salts in seawater at one location. A 300.-gram sample of the seawater was placed in an open container. After a week, all the water had evaporated and 10. grams of solid salts remained in the container.

73 Determine the concentration, expressed as percent by mass, of the dissolved salts in the original sample of seawater. [1] -

74 At standard pressure, compare the freezing point of seawater to the freezing point of distilled water. [1]

75 Explain why the evaporation that occurred during the investigation is an endothermic process. [1]