Bowen_Chpt 12_Solution

CHAPTER 12

Classification of Matter

Soluble

Soluble – is to be capable to be dissolved, broken down.

A solution is the homogeneous mixture in a single phase.

Solution

Salt Carbon dioxide Sugar

Solute

A solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

Solvent

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Suspensions and Colloids

Suspensions and colloids are NOT solutions.

Suspensions: The particles are so large that they settle out of the solvent if not

constantly stirred.

Colloids: The particles intermediate in size

The Tyndall Effect

Colloids scatter light, making a beam visible.

Solutions do not scatter light.

Which glass

An electrolyte is:

A substance whose aqueous solution conducts an electric current.

A nonelectrolyte is:

A substance whose aqueous solution does not conduct an electric current.

Try to classify the following substances as electrolytes or nonelectrolytes…

1.Pure water

2.Tap water

3.Sugar solution

4.Sodium chloride solution

5.Hydrochloric acid solution

6.Lactic acid solution

7.Ethyl alcohol solution

8.Pure sodium chloride

ELECTROLYTES: NONELECTROLYTES:

Tap water (weak) NaCl solution

HCl solution

Lactate solution (weak)

Pure water

Sugar solution Ethanol solution Pure NaCl

But why do some compounds conduct electricity in solution while others do not…?

Rates of dissolution

1. Increasing the surface area allows the breaking down of the solute.

a. This is why clumps of sugar take longer to dissolve.

2. Heating – increases the dissolving, because the solvent particles move faster.

Saturation and Equilibrium

Saturation of Solutions

 A solution that contains the maximum amount of

solute that may be dissolved under existing conditions is saturated.

 A solution that contains less solute than a

saturated solution under existing conditions is

unsaturated.

 A solution that contains more dissolved solute

• When deciding what type of solvent to use (to dissolve the solute) it is important to identify what types of substances you have.

1. Polar (partial + or – charges) 2. Nonpolar (equal sharing of e-) • Remember the rule:

Polar vs. Non-Polar

• Remember electronegativity tends to decrease down a group and increase across a period.

• Electronegative atoms attracts electrons more strongly.

• Water is a polar solvent and is

attracted to polar solutes.

• Salt is made from an ionic bond. • Water molecules surround and

isolate the surface ions. The ions become hydrated and move away from each other in a

process called dissociation.

• Hydration is when a solution is

made by using water as the solvent.

• Hydrates are crystals formed

from solutions. They retain specific ratios of water

Solubility Trends

 The solubility of MOST solids increases with

temperature.

 The rate at which solids dissolve increases with

increasing surface area of the solid.

 The solubility of gases decreases with increases

in temperature.

 The solubility of gases increases with the

Liquid solutes and solvents

 Immiscible – liquid that are not soluble with each

other.

 “Oil and water don’t mix”

 Definite line between the materials

 Miscible – liquids that freely

Effect of Pressure on Solubility

 Henry’s Law – The

solubility of a gas in a liquid is directly

porportional to the

partial pressure of that gas on the surface.

 Carbonated drinks must increase the pressure to

get CO₂ gas to be soluble in the beverage.

 5 -10 atms

 Effervescence – the rapid

DNW

Therefore…

Solids tend to dissolve best when:

o _Heated

o Stirred

o Ground into small particles

Gases tend to dissolve best when:

o The solution is cold

o Surface pressure is higher then air

Concentration

Concentration of a solution is the measure of the amount of solute in a given amount of

solvent.

Concentration is not a very definite measurement.

We will learn two different ways to determine concentration.

1. Molarity

2. Molality

Molarity

The concentration of a solution measured in moles of solute per liter of solution.

M =

mol

(solute)

L

)

You have 3.5L of a solution, that contains 90.0g of NaCl. What is the molarity ?

step 1. convert grams to moles. step 2. plug values into eqtn

M =

1.54 mol

3.5L

=

.44 M NaCl

Molality

The concentration of a solution in moles of solute per kilogram of solvent.

Since the most common solvent, water, has a density of 1 kg/L or 1g/1mL, one kilogram of water is the same as one liter of water!

What is the molality of 17.1g of C₁₂H₂₂O₁₁ in 125g of H₂O.

Step 1. Convert Step 2. Plug in

m

= mol

(solute)

Kg

(solvent)

m

=

.049mol

Percent Concentration

Percent Concentration by Mass (%)

This is the mass of the solute divided by the mass of the solution (mass of solute plus mass of solvent),

multiplied by 100.

Make sure the units of the solute and the solution are the same.

Example: Determine the percent concentration by

mass of a 100 g salt solution which contains 20 g salt. Solution:

Percent Concentration

Percent Concentration by Volume (%)

This is the volume of the solute divided by the volume of the solution (volume of solute plus volume of

solvent), multiplied by 100.

Make sure the units of the solute and the solution are the same.

Example: Determine the percent concentration by Volume of a 25mL methyl alcohol when added to 435mL of H₂O.

Solution:

Molarity Conversion

M₁ V₁ = M₂ V₂

Used to determine the quantity of a given molar amount to make a new molar amount.

Taking a higher concentration to a lower concentration typically (diluting)

If you are solving for the new volume ,

a. The V you solve for would be the total volume of the solution

Molarity Conversion

M₁ V₁ = M₂ V₂

If you have 600ml of 3 M solution , what would the new volume be of a 1.75 M solution????

(3M)(600ml)=(1.75M)(V₂) 1.75M 1.75M

V₂ = 1028 ml of 1.75M solution

How much solvent did you add to create the total solution?

1028 -600 =

Solution Stoichiometry- is just like any other kind of Stoichiometry.

We will be using the Molarity or Molality to

determine the amount of moles required, or volume of solution need to complete a reaction.

Example:

When you use 25ml if 4 M HCl to produce H_2(g) , how many grams of zinc are need to completely react?

Step 1. write a balanced eqtn

HCl + Zn  ZnCl₂ + H₂

Step 2. Calculate how many moles of HCl you have?

4M = x mol HCl 0.025 L

2 1 1 1

x = 0.1 mol HCl

Solution Stoichiometry Honors only

2 HCl + 1 Zn  1 ZnCl₂ + 1 H₂

Step 3. Use Stoich to calculate the amount of ____ need

0.1 mol HCl x 1 mol Zn x 65.39 g Zn = 1 2 mol HCl 1 mol Zn

What is the volume of gas that would be produced if @ STP? (Gas Stoich)

0.1 mol HCl x 1 mol H₂ x 22.4 L H₂ = 1 2 mol HCl 1 mol H₂

3.27 g Zn

Solution Stoichiometry Honors only

We can even have Limiting/Excess Reactant problems with this!!!!!

How many grams of magnesium hydroxide will

precipitate if 55.0 mL of 0.35 M Mg(NO₃)₂ are combined with 35.0 mL of 0.20 M KOH?

Step 1 Calculate the # of moles of each solution

.35 M Mg(NO₃)₂ = x mol Mg(NO₃)₂ .20 M KOH = x mol KOH

.055 L .035L

x= .019 mol Mg(NO₃)₂ x= .007 mol KOH

Step 2 Do both stoich…..

.019 mol Mg(NO₃)₂ x 1 mol Mg(OH)₂ x 58.33g Mg(OH)₂ = 1 mol Mg(NO₃)₂ 1mol Mg(OH)₂

.007 mol KOH x 1 mol Mg(OH)₂ x 58.33g Mg(OH)₂ = 2 mol KOH 1mol Mg(OH)₂