Chapters 12 and 13

What have we covered already?

So far this year, we have already covered:• Molarity (remember M = mol /L)

• Writing net ionic equations for single replacement and double replacement reactions.

• Identifying spectator ion(s).

• Using the solubility rules to determine if a precipitate has formed in a double replacement reaction.

Section 12-1:3 Types of Mixtures

Solutions (sugar dissolved in water)

Colloids (fog; milk)

Suspensions (muddy water)

SolutionsA solution is a homogeneous mixture of 2 or

more substances in a single phase.The solute is the substance being dissolved.

It is present in smaller quantity.The solvent is the dissolving medium. It is

present in larger quantity.

Salt + Water → Salt Water

(solute) (solvent) (solution)

Any phase of matter can be the solute or the solvent…

Here are some examples:Solute State Solvent State

Example(1) gas (O2) gas (N2) air(2) gas (CO2) liquid (H2O) seltzer(3) liquid (alcohol) liquid (H2O) rubbing

alcohol(4) solid (salt) liquid(H2O) salt water(5) solid (carbon) solid (iron) steel

** A homogeneous mixture of 2 solids is called an…..ALLOY!**

Some properties of solutions

Solute particles are very small. In fact, once dissolved, they are too small to see.

Because the solute particles are so small, they CANNOT be separated from the solvent with a filter.

Solutions are always homogeneous.Solutions do NOT scatter a beam of light.

ColloidsA colloid is a heterogeneous mixture

containing solute particles of intermediate size that remain dispersed throughout the solvent.

Colloids are EVERYWHERE! Some common examples are:

milk mayonnaise fog smoke paint

Propeties of ColloidsColloids are heterogeneous mixtures.The solute particles are medium in size

(larger than a solution but smaller than a suspension).

The solute particles CANNOT be separated from the solvent using a filter (still too small).

The solute particles remain dispersed throughout the solvent. They do NOT settle out.

SuspensionsA suspension is a heterogeneous mixture

with solute particles so LARGE that they settle to the bottom.

The solute particles are large enough to be separated from the solvent using a filter.

Given enough time, the solute particles will settle out.

Quite often, the upper portion of a suspension will also scatter a beam of light.

What is the Tyndall Effect?The Tyndall Effect

occurs when a beam of light is scattered by the solute particles in a colloid.

It is the best way to distinguish between a solution and a colloid.

Electrolytes and Non-electrolytes

Substances that dissolve in water can be classified according to whether they produce dissociated ions in solution or not.

We can therefore classify those substances that dissolve in water in one of 3 ways:(1) Strong Electrolytes(2) Weak Electrolytes(3) Nonelectrolytes

Strong vs. Weak ElectrolytesStrong Electrolytes Weak Electrolytes

Strong electrolytes are substances that dissolve in water and dissociate

(i.e., break apart) 100% into ions.

The resulting aqueous solution strongly conducts an electric current.

Example-NaCl (s) → Na+ (aq) +

Cl- (aq)

Weak electrolytes are substances that dissolve in water and dissociate but LESS than 100% into ions.

The resulting aqueous solution weakly conducts an electric current.

Example-Vinegar

NonelectrolytesA nonelectrolyte is a substance that

dissolves in water but there is NO dissociation into ions.

The solute remains as undissociated, intact molecules.

The resulting aqueous solution does NOT conduct an electric current at all .

Molecular or covalent compoundsare often nonelectrolyes. The bestexample is sugar.

Section 12-2: The Solution Process3 Factors Affecting the RATE of Solution (i.e.,

how fast a solution forms) (1) Crushing the solute

(this increases the surface area of the solute)

(2) Stirring the solution(this brings fresh solvent into

contact with the solute)

(3) Heating the solvent(this increases kinetic energy

so all the particles move faster)

Saturation and Solubility If you add spoonful after

spoonful of sugar to tea, eventually no more sugar will dissolve.

For every combination of solute and solvent at a given temperature, there is a limit to the amount of solute that will dissolve.

We can describe how much solute is dissolved in a given quantity of solvent qualitatively using saturation levels.

(1) An unsaturated solution contains LESS than the maximum amount of dissolved solute.

(2) A saturated solution contains EXACTLY the maximum amount of dissolved solute.

(3) A supersaturated solution contains MORE than the maximum amount of dissolved solute.

What is solubility?The solubility of a

substance is the amount of that substance required to form a saturated solution (i.e., containing the maximum amount of solute) in a given quantity of solvent at a specified temperature.

Solubilities are determined experimentally.

What are the factors that affect solubility?(i.e., how MUCH of a solute you can dissolve)(1) Polarity of the Solute and SolventThe three most important words in all of chemistry are: “LIKE DISSOLVES LIKE”.In other words: polar solutes dissolve in polar solvents and nonpolar solutes dissolve in nonpolar solvents.

Salt dissolves in water Oil and water

because salt is ionic do not mix (extremely polar) and because oil iswater is very polar very nonpolaras well. and water is

polar.

(2) PressureChanging the pressure can

greatly impact the solubility of a gas dissolved in a liquid.

Henry’s Law states that the solubility of a gas dissolved in a liquid is directly proportional to the pressure of the gas.

In other words:higher pressure, higher solubilitylower pressure, lower solubility

Effervescence!!When you open a soda can, the CO2 rapidly escapes because the volume available to the gas suddenly increases so the pressure suddenly decreases!It’s Henry’s Law!!

(3) Effect of Temperature on Solubility(A) Effect of Temperature on the Solubility of a

Gas Dissolved in a LiquidQuestion?- What will make soda stay carbonated longer– keeping it at room temperature or in the refrigerator?

Why?

(B) Effect of Temperature on the Solubility of Solids Dissolved in LiquidsThe only way to

determine this is by consulting a solubility curve.

For most solutes, more dissolves at a higher temperature (KNO3).

But for some solutes, less dissolves at a higher temperature (Li2SO4).

Now why is this so?Solutes with a Positive Heat of Solution

Solutes with a Negative Heat of Solution

When a solute with a positive heat of solution dissolves in water, heat must be absorbed to make the solute dissolve. Remember we called this endothermic.

This will feel COLD to the touch.

The solubility will increase at higher temperatures.

Example- sodium thiosulfate demo

When a solute with a negative heat of solution dissolves in water, heat must be released to make the solute dissolve. Remember we called this exothermic.

This will feel HOT to the touch.

The solubility will decrease at higher temperatures.

Example- sodium hydroxide demo

Osmosis If two solutions are separated

by a semi-permeable membrane (lets small things through but not big things), solvent (water) will flow through the membrane.

Osmosis is a natural phenomenon; you do not need to do anything to make it happen.

Osmosis is the flow of solvent through a semi-permeable membrane from the side of low solute concentration to the side of high solute concentration.

Very often in the lab, we take concentrated solutions (those that have a high molarity) and dilute it with water to make a more dilute solution (having a lower molarity).

To solve a serial dilution problem, you will use the following formula:

M1V1 = M2V2

Serial dilution problems often involve solving for the volume of the original solution (V1) to use AND how much water to add to reach the new volume (V2).

Let’s solve the following 2 problems:(1)You have 6 M. HCl (aq) and need to make 500 mL of 1.0 M HCl (aq). What volume of the stock solution do you need? How much water do you need to add?

(2)You take 250 mL of 12 M. HNO3 (aq) and add 750 mL of water. What is the final molarity of your new solution?