How would the presence of sodium chloride in water effect its evaporation tendency ?
The presence of sodium chloride in water will lower its evaporation tendency, thereby increasing its boiling point above 1000C. In other words, a solution of NaCl in water will boil at a temperature higher than 1000C. This is because in pure water only water molecules are present and in NaCl solution, both water molecules as well as Na+ and Cl- ions would be present. Therefore in the solution, the surface has both solvent and solute particles. As a result, the number of water molecules present at the surface of solution would be less than in pure water. On boiling, the water goes into the vapour state. In case of solution, as less water molecules are there on the surface, hence the number of water molecules which go into the vapour state reduces, and so the evaporation tendency decreases.