Chemistry Homework #9

Pg 62 #1-3

1.     Suppose you dissolved 40 g potassium chloride (KCl) in 100 g water at 50 degrees Celsius. You then let the solution cool to room temperature, about 25 degrees Celsius.

A.     What changes would you see in the beaker as the solution cooled?

·      There would be no change in the solution as the beaker cooled.

B.     Draw models of what the contents in the beaker would look like at the particulate level at 50 degrees, 40 degrees, and 25 degrees Celsius.

50 degrees:

40 degrees: 

25 degrees: 

2.     An unsaturated solution will become more concentrated if you add more solute. Decreasing the total volume of water in the solution (such as by evaporation) also increases the solution’s concentration. Consider a solution made by dissolving 20 g KCl in 100 g water at 40 degrees Celsius.

A.     Draw a model of this solution.

B.     Supposed that while the solution was kept at 40 degrees Celsius, one-fourth of the water evaporated.

·      Draw a model of this final solution and describe how it differs from your model of the original solution. 

It differs from the original solution because it has more atoms of each element in it.

·      How much water must evaporate at this temperature to create a saturated solution?

o   20 grams must evaporate

3.     A solution may be diluted (made less concentrated) by adding water.

A.     Draw a model of a solution containing 10 g KCl in 100 g water at 25 degrees Celsius.

B.     Suppose you diluted this solution by adding another 100 g water with stirring. Draw a model of this 25 degree new solution

C.     Compare your models in Questions 3a and 3b. What key feature is different in the two models?

·      The key feature that is different in the two models is that in 3a, the model has more Potassium chloride, while in 3b, the model has more water because it is diluting the solution.