1. A. unsaturated, B. still saturated, C. supersaturated
QUESTION:
The solubility of sodium nitrate in water is 85 g NaNO3 per 100 g of water at 20oC. At 50oC, the solubility is 115 g NaNO3 per 100 g of water. A saturated solution of NaNO3 is prepared by mixing 150 g of NaNO3 and 100g of water at 20oC. When this mixture is heated to 50oC, the resulting solution will be
A. unsaturated, B. still saturated, C. supersaturated
The solubility of sodium nitrate in water is 85 g sodium nitrate per 100 g of water at 20oC. At 50oC, the solubility is 115 g sodium nitrate per 100 g of water. A saturated solution of nitrate is prepared by mixing 150 g of sodium nitrate and 100g of water at 20oC. When this mixture is heated to 50oC, the resulting solution will be
A. unsaturated, B. still saturated, C. supersaturated
PAUSE
CLICK
Solubility refers to the concentration of a saturated solution. It is the maximum concentration that a solute can have
in a given solvent at a given temperature.
We are given the solubility of sodium nitrate is 85 grams per 100g of water at 20 degrees.
HIGHLIGHT information in question
Since we’re mixing more than 85 grams…
HIGHLIGHT 150 grams
We would expect to get a saturated solution at 20 degrees. 85 out of the 150 grams of sodium nitrate will dissolve
And the remaining 65 grams will remain undissolved. This, in fact, illustrates the way to prepare a saturated solution.
Add enough of the solute until no more will dissolve. In a saturated solution, we say that the solution is in equilibrium
HIGHLIGHT equilibrium
with the undissolved solid. By this, we mean that solute particles will be moving between the solution phase
and the solid phase at equal rates.
So what happens when we heat the solution to 50 degrees. According to the information given in the problem,
we can now dissolve up to 115 grams of sodium nitrate in 100g of water.
This is still less than the 150 grams that we started with minus 115 equals 35 Therefore, 35 grams will
remain undissolved. This means that we will still have a saturated solution.
The correct answer is B.
PAUSE END RECORDING
Concentration of saturated solution = solubility
At 20oC: 85 g of NaNO3 will be dissolved, 65 g will remain undissolved. Solution is saturated, is in equilibrium with undissolved solid.
At 50oC: 115 g of NaNO3 will be dissolved, 35 g will remain undissolved. Solution is saturated.

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08