BOILING POINT OF A SOLUTION

Question

How many moles of ions are formed in aqueous solution when 1 mol of Sr(OH)2 dissolves in water? Explain its effect in the freezing and boiling point of a solution

Answer 1

This is question about colligative properties. Sr(OH)2 is composed of 3 total molecules -- that is, it will dissolve into 1 Sr2+ and 2 OH- ions. Thus, 1 mole of Sr(OH)2 will form 3 moles of ions in aqueous solution.

In general, adding solute to a solution results in boiling point elevation and freezing point depression. For example, adding salt to ice/water results in freezing point depression. This means that water with salt in it will require a lower temperature to freeze -- this is why we salt roads in the winter to prevent the formation of ice!

The extent of BP elevation of freezing point depression is dependent on the number of ions in the solution. Thus, 1 mol of Sr(OH)2 will have a greater effect than 1 mol of NaCl. Why? Because each mol of NaCl provided only 2 ions, whereas each mole of Sr(OH)2 provides 3.