a) How many grams of KNO_3 should be added to 100 mL of water at 25°C to make a saturated solution?
b) The solubility of KNO_3 increases as temperature increases. When KNO_3 dissolves, is the process endothermic or exothermic?
c) When CaCl_2 dissolves, the process if exothermic. Is CaCl_2 more soluble at high temperature or low temperatures?
a) To determine the number of grams of KNO3 needed to make a saturated solution, we need to know the solubility of KNO3 at 25°C. The solubility is usually given in grams of solute per 100 mL of water. Let's say the solubility of KNO3 at 25°C is 50 grams per 100 mL of water.
To make a saturated solution, we need to add enough KNO3 to reach its solubility limit. Since we have 100 mL of water, we can calculate the amount of KNO3 needed as follows:
Amount of KNO3 = Solubility of KNO3 × Volume of water
Substituting the values, we get:
Amount of KNO3 = 50 g/100 mL × 100 mL = 50 grams
Therefore, you need to add 50 grams of KNO3 to 100 mL of water at 25°C to make a saturated solution.
b) When KNO3 dissolves, the process is endothermic. This means that it absorbs heat from its surroundings as it dissolves. The increase in temperature helps break the bonds in the KNO3 solid, allowing it to dissolve more easily.
c) When CaCl2 dissolves, the process is exothermic. This means that it releases heat into its surroundings as it dissolves. With an exothermic process, the solubility of CaCl2 decreases with increased temperature. Therefore, CaCl2 is more soluble at low temperatures rather than high temperatures.