# Exercises

## Q6-1

What is a solution?

## Q6-2

Please give an example of a solution

## Q6-3

How do you know it is a solution (and not a mixture)?

## Q6-4

When something dissolves, what happens to it?

## Q6-5

If you add 5 g of salt to 100g of water and allow it to dissolve, what is the resulting mass?

A) solute

B) solvent

C) concentration

## Q6-2

A) If you have 200 mL of a 1.5 M solution of glucose (C6H12O6), how many moles of glucose are in the solution?

B) What mass of glucose is in that volume of solution?

C) If you needed a 0.050 M solution of glucose, and you only had the solution in 2a, what would you do?

D) If you needed a 0.050 M solution of glucose, and you only had the solution in 2a, what would you do?

## Q6-3

How would you prepare 100 mL of a 0.15 M solution of sodium chloride?

## Q6-1

Draw the Lewis structure for ethanol CH3CH2OH

## Q6-2

What intermolecular forces are present in ethanol? Explain why you think they are present.

## Q6-3

If ethanol dissolves in water what interactions would be present between the water molecules and the ethanol molecules? Draw a representation showing the interactions.

## Q6-4

If ethanol dissolves in water, which changes would require an energy input from the surroundings? Which would produce energy?

## Section 6-4

Here is the table from the text:

 Compound Molar mass (g/mol) Structure Solubility (g/L) 20 ºC Propane 44 CH3CH2CH3 0.07g/L Ethanol 46 CH3CH2OH Completely miscible Dimethyl ether 46 CH3OCH3 328 g/L Pentane 72 CH3CH2CH2CH2CH3 0.4 g/L Butanol 74 CH3CH2CH2CH2OH 80 g/L Diethyl ether 74 CH3CH2OCH2CH3 69 g/L hexanol 102 CH3CH2CH2CH2CH2CH2CH2OH 0.4 g/L 1,6 hexanediol 226 HOCH2CH2CH2CH2CH2CH2CH2OH 500 g/L Glucose 180 C6H12O6 910g/L

## Q6-1

How do you distinguish which compounds are soluble or insoluble, is it a “yes/no” question?

## Q6-2

Which of these compounds would you say are soluble in water?

## Q6-3

Draw a Lewis structures for propane, ethanol, and dimethyl ether.

## Q6-4

What possible interactions are there between the solute and solvent for each substance? Draw them.

## Q6-5

Do the types of interactions allow you to predict relative solubilities?

## Q6-1

You make a solution using a solid solute (5g) in water (total volume 100 mL). The molar mass of the solute is 110 g/mol

A) What is the molarity?

B) What is the concentration reported as % by mass? (assuming the density of water is 1g/mL)

C) What is different about these two concentration units? (why would you use one rather than another?)

## Q6-2

When you make the solution, all the solute dissolves and the temperature rises, what does that allow you to say about:

A) ΔG for solution

B) ΔH for solution

C) ΔS for solution

D) The relative strengths of the interactions before mixing (solute-solute, and solvent-solvent), and after mixing (solute-solvent)

## Q6-1

What kind of bonding is present in CaCl2? (How do you know?)

## Q6-2

Draw a picture of CaCl2 solid. Be sure to take into consideration how it looks (size and the relationship between Ca and Cl).

## Q6-3

CaCl2 is soluble in water. Draw a picture of what the solution might look like, showing water molecules, the Ca and the Cl species.

## Q6-4

What property does a solution of CaCl2 have that a solution of sugar does not? (It may help if you draw what an aqueous solution of sugar would look like.) How could you test your predictions?

## Q6-1

A) Take the first baggie, which contains CaCl2, and add a few drops of water to the white power. What happens? Record your observations.

 Is thermal energy released from, or absorbed by the system? What is the sign of ΔG for this process? How do you know? What is the sign of ΔH for this process? How do you know What is the sign of ΔS for this process? How do you know

B) What do you think is happening? Why is there a temperature change? Does this explain why the white powder is soluble?

## Q6-2

A) Now take the second baggie (which contains NH4Cl) and repeat. Record your observations.

 Is thermal energy released from, or absorbed by the system? What is the sign of ΔG for this process? How do you know? What is the sign of ΔH for this process? How do you know What is the sign of ΔS for this process? How do you know

## Q6-3

In light of your observations – what thermodynamic factors do you think are important to understand for the process of solubility?

## Section 6-8

For each solute, and solvent indicate what interactions are present, what interactions are present between the solute and solvent in solution. (draw structures showing interactions)

 Solute Solvent Solution CH3OH H2O CH3OH CH3COOH CaCl2 H2O NH4Cl H2O CaCl2 Hexane (C6H14)

## Section 6-9

For each of the following solutions use the experimental evidence given to predict what happens when the solvent is mixed with the solute.

## Q6-1

CH3OH is completely soluble in water in all proportions: when they mix the temperature increases. Predict the sign of ΔH, ΔS and ΔG, and explain your reasoning by drawing molecular level pictures

## Q6-2

The solubility of NaCl is 359 g/L at 298K. When it dissolves the temperature drops. Predict the sign of ΔH, ΔS and ΔG, and explain your reasoning by drawing molecular level pictures.

## Q6-3

Calcium phosphate (Ca3(PO4)2) is insoluble in water. The ΔH for solution is about zero. Predict the signs of ΔS and ΔG, and explain your reasoning by drawing molecular level pictures