Effects of Solutes in Solution

Define: boiling point, freezing point and electrolytes.

Explore the effect of solutes on the boiling point and freezing point of solutions (colligative properties).

Describe the behavior of electrolytes in a solution.

AimHow do solutes

affect the properties of the solution?

Essential Questions

1. What effects do solutes have on the boiling and freezing points of solvents?

2. What forces are responsible for these effects?

3. How does the presence of electrolytes affect a solution?

Key Wordsboiling point, freezing

point, elevation,

depression, ions,

electrolytes,

conductivity

What is the Boiling Point of Water at STP?

H2O

B.P. (Boiling Point) = __________

F.P. (Freezing Point = _________

What are the Effects of Solutes on the Boiling and

Freezing Points of Solvents

Predict what happens to the B.P. and the F.P. of water when NaCl is added?

F.P. _______ B.P. _________

Boiling Point Elevation

Recall Boiling is transition between two states of matter

Recall the following concept covered last semester: what attractions/forces are responsible for states of

matter.

Intermolecular Forces!

Examples of Intermolecular forces

What kind of intermolecular forces are

at play between NaCl and H2O?

_______________________________________

Molecule-Ion Attraction

The intermolecular force

between NaCl and water are

very strong and therefore,

very hard to break.

How is this related to the

boiling point elevation of the

solution?

______________________________

_

Freezing Point Depression

Hint: Solids Consist of a Rigid Crystalline

Structure

Why does the presence of solutes lower the freezing points of solvents?

Solutes Get in the Way!

When solutes are present, it becomes more difficult for water molecules to connect with each other in order to form a rigid solid shape.

Also, solutes interact with solids to dissolve the solid. In the same way that water dissolves solutes, solutes dissolve ice (example: NaCl).

Complete the Following Dissolving

“Reactions”

A. C12H22O11(s) + H2O(l) __________________________

1. How many different particles will be “floating”

in water? Which one(s)?

_____________________________________________

Deduction Question

A. NaCl(s) + H2O(l) __________________________________________

1. How many different particles are “floating” in solution? Which one(s)?

____________________________________________________________________________________

_

B. CaCl2(s) + H2O(l) _________________________________________

1. In how many parts does CaCl2 break up? Which one(s)?

____________________________________________________________________________________

_

C. From NaCl and CaCl2, which salt do you predict will be more effective in

melting the snow? Explain?

________________________________________________

____________________________________________________________________________

Hypothesize!

According to your answers to the previous question, what conclusion can be drawn? Explain.

____________________________________________________

____________________________________________________

Hypothesize!

What conclusion can be drawn from the diagram?

_________________________________________________________

_________________________________________________________

NotesIV. Effects of Solute on Solvent Properties

A. Boiling Point Elevation – a rise in boiling point of a solution caused by the presence of solutes (ex. addition of antifreeze to car radiators to prevent the water from boiling).

B. Freezing Point Depression – a lowering of the freezing point of a solution caused by the presence of solutes (ex. using salt to melt ice).

C. Colligative Properties – Properties that depend on the number of solutes and the nature of the solvent but NOT on the identity of the solute. i. Boiling point elevation and freezing point depression

are colligative properties. ii. The more particles of solute a solution contains, the

more the affect on boiling & melting points.Number of solute : B.P. of Solvent : F.P. of Solvent

Does Water Conduct

Electricity?

Can we add something to the water to make it

conduct electricity?

If so, what can we add?

NaCl

v.s.

Sugar

Does solid NaCl Conduct Electricity by itself, without water?

What happens in the dissolving of sodium

that allows it to conduct electricity in

solution?

NotesD.Conductivity – conductivity of electrical

current by a solution caused by the presence of electrolytic solutes. 1. Electrolytes – are solutes that

dissociate/ionize (separate into ions) in water and are therefore, able to conduct electricity in solution form (Ex: Salts).

2. Electricity - the flow of charges (such as ions in solution or electrons in metallic bonds).

Video

Electrolytes Animation

http://youtu.be/aELPrWzixeU

Learning Check1. When ethylene glycol (an antifreeze) is added to

water, the boiling point of the watera. decreases, and the freezing point decreasesb. decreases, and the freezing point increasesc. increases, and the freezing point decreasesd. increases, and the freezing point increases

2. Which solution will freeze at the lowest temperature?

a. 1 mol of sugar in 500 g of waterb. 1 mol of sugar in 1000 g of waterc. 2 mol of sugar in 500 g of waterd. 2 mol of sugar in 1000 g of water

Learning Check3. A 1-Kilogram sample of water will have the

highest freezing point when it contains3. 1 x 1017 dissolved particles c. 1 x 1021 dissolved particles4. 1 x 1019 dissolved particles d. 1 x 1023 dissolved particles

4. At standard pressure, an aqueous solution of sugar has a boiling point

a. greater than 100°C and freezing point greater than 0°Cb. greater than 100°C and freezing point less than 0°Cc. less than 100°C and a freezing point greater than 0°C d. less than 100°C and a freezing point less than 0°C

5. Which solution containing 1 mole of solute dissolved in 1000 grams of water has the lowest freezing point?a. KOH(aq) b. C6H12O6(aa) c. C2H5OH(aq) d. C12H22O11(aq)

NotesEffects of Solutes on the Properties of Solvents

NotesIV. Effects of Solute on Solvent Properties

A. Boiling Point Elevation – a rise in boiling point of a solution caused by the presence of solutes (ex. addition of antifreeze to car radiators to prevent the water from boiling).

B. Freezing Point Depression – a lowering of the freezing point of a solution caused by the presence of solutes (ex. using salt to melt ice).

C. Colligative Properties – Properties that depend on the number of solutes and the nature of the solvent but NOT on the identity of the solute. i. Boiling point elevation and freezing point depression

are colligative properties. ii. The more particles of solute a solution contains, the

more the affect on boiling & melting points.Number of solute : B.P. of Solvent : F.P. of Solvent

NotesD.Conductivity – conductivity of electrical

current by a solution caused by the presence of electrolytic solutes. 1. Electrolytes – are solutes that dissociate/ionize

(separate into ions) an aqueous solution and as a result, the solution is able to conduct electricity (Ex: salts such as NaCl or CaCl2).

2. Electricity - the flow of charges (such as ions in solution or electrons in metallic bonds).

3. The higher the concentration of ions within a solution, the greater the degree of conductivity of a solution.