Question #1497c

1 Answer
Feb 25, 2017

Answer:

At about #46^@"C"#.

Explanation:

In order to be able to answer this question, you must have some information about how the solubility of potassium nitrate, #"KNO"_3#, changes with temperature.

A useful tool to have at your disposal is the solubility graph for potassium nitrate, which looks like this

http://www.mts.net/~alou/Chemistry%2011/Unit%204%20-%20Solutions%20Lessons/Lesson%203%20-%20Factors%20Affecting%20Solubility.htm

Your goal is to find the temperature at which #"80 g"# of potassium nitrate will dissolve in #"100 mL"# of water. Notice that the solubility of the salt is given in grams per #"100 g"# of water, which means that you'll have to convert the volume of water to grams.

Since no additional information was provided, you can assume that the density of water is equal to #"1.0 g mL"^(-1)#, which implies that your sample has a mass of

#100 color(red)(cancel(color(black)("mL"))) * "1.0 g"/(1color(red)(cancel(color(black)("mL")))) = "100 g"#

Now, look for #80# on the vertical axis of the graph and draw a horizontal line until you hit the solubility curve, which is shown here in #color(darkgreen)("green")#.

From the point of intersection, draw a vertical line until you intersect the horizontal axis, i.e. the axis that shows the temperature.

Your line should fall somewhere in between #40^@"C"# and #50^@"C"#, a little closer to the #50^@"C"# mark.

You can thus say that you can dissolve #"80 g"# of potassium nitrate in #"100 g"# of water at about #46^@"C"#.