Solubility Graph

I am always searching for new, fun crystal growing recipes. Crystals of table sugar and table salt are favorites, mainly because the chemicals are so readily available.

The solubility graph shown provides information about the amount of sugar and salt that can be dissolved at different temperatures.

When you mix sugar and water, the mixture is called a solution. The solute (sugar) is being dissolved in the solvent (water).

Question: Can more sugar be dissolved if the water is heated?

Answer: The blue line on the graph represents the amount of sugar that is dissolved in 100 ml of water.  Notice how the blue line curves upward.

Starting Point: At zero degrees Celsius, about 175 grams of sugar can be dissolved in 100 ml of water. The solution would be saturated with sugar. This means that no more sugar would dissolve. If you added more sugar, no matter how long you stir the solution, this extra sugar would sink to the bottom of the container. A saturated solution is at its maximum concentration (amount of sugar that can be dissolved in water at this temperature).

Ending Point: At 100 degrees Celsius, about 500 grams of sugar can be dissolved in 100 ml of water. Again, the solution is saturated with sugar.

Yes, more sugar can be dissolved if the water is heated.

Question: Can more salt be dissolved if the water is heated?

Answer: The black line on the graph represents the amount of salt that is dissolved in 100 ml of water. Notice how the black line is almost straight across the graph—horizontal.

Starting Point: At zero degrees Celsius, about 38 grams of salt can be dissolved in 100 ml of water.The solution is saturated with salt.

Ending Point: At 100 degrees Celsius, about 40 grams of salt can be dissolved in 100 ml of water. The solution is saturated with salt.

Heating the water to its boiling point changes the amount of salt that can be dissolved by about 2 grams, this is about one-fifth of a teaspoon. While a tiny bit more salt can be dissolved, it is not enough to make much difference. Thus, heating water is not necessary to make a concentrated salt solution.