Regents Chemistry Exam august 2022
39. Based on Table G, which sample, when added to 100. grams of water and thoroughly stirred, produces a heterogeneous mixture at 20.°C? (1) 20. g of KCl
(2) 20. g of KI
(3) 80. g of KCl
(4) 80. g of KI
Explanation: A heterogeneous mixture is not uniform. If all of KCl or KI would be dissolves in water, the mixture would be uniform and homogeneous. If it is heterogeneous, that means not all of the solute got dissolved. Looking at table G, if we are below the line (either KCl or KI for this question) that means the solution is unsaturated (more solute can be dissolved). If we are on the line that means solution is saturated, maximum amount of solute has been dissolved and above the line means supersaturated (more than maximum has been dissolved and will easily precipitate out).
First we identify all of the points on the graph. We locate the 20 degree temperature on the x axis. Then we locate the correct points of the grams of solute added (20 g and 80 g) as I have shown on the graph. 20 g of KCl fall under the KCl line making the solution unsaturated. 20 g of KI fall under the KI line making the solution unsaturated. 80 g of KI fall under the KI line making the solution unsaturated. 80 grams of KCl fall above the KCl line making the solution supersaturated, which will result in the solute precipitating (coming out of the solution). The will make the mixture heterogeneous.