Solutions and Solubility

Essential Questions

1. What’s a solution vs mixture?2. What’s the difference between a solution,

solvent and solute?3. Can do you quantify concentration?4. What do some things dissolve while

others do not?5. How can we increase the rate that

something dissolves?

What happens when stuff dissolves?

http://www.youtube.com/watch?v=0cPFx0wFuVs

Mixtures and Solutions

Remember back to the beginning of the year when we learned about mixtures!

Concept check: Identifying Mixtures

Identify the follow as homo or heterogenous:Milk OilMuddy water IronBrass BloodPaint WaterSoda Sugar waterFlat Soda Toothpaste

Heterogeneous Mixtures

There are two types of heterogeneous solutions: Suspensions: mixtures containing particles that

will settle out if left undisturbed. Examples: oil and water, sandy water, muddy water,

paint, and flour in water

Colloids: mixtures of smaller sized particles that do not settle out on their own

Examples: milk, blood, butter, smoke, spray deodorant, motor oil

Homogenous Mixtures

Also called solutionsCan be solids, liquids or gasesSingle phaseRemain mixed; particles DO NOT settle outCannot be separated by filter paper

Solutions

A solution is formed when a solute dissolves in a solvent forming a homogeneous mixture

Solutions

Solvent – present in the greatest amount

Solute – present in the lesser amountSolution – Mixture of 2 or more

substances that are a mixed homogeneously

Identify the solvent and solute?

Solution Solvent SoluteFlat Soda Water Sugar syrupLemonade Water Lemonade mix

Alloy like brass Copper Zinc

Air Nitrogen Oxygen

Antifreeze Water Antifreeze

Ocean Water Water salt

Antifreeze Close up

In 1885 Karl Benz of Germany invited the first radiator for cars

Before this, car engines were cooled with water and needed to be constantly refilled!

Antifreeze has ethylene glycol added to water to elevate the boiling point and depress the freezing point

Solvent Joke

WATER AS A SOLVENT

Water is the most effective solventWater will dissolve many ionic

compounds and most polar covalent compounds

Water is not effective as a solvent for non-polar covalent compounds

Effectiveness of water is because water is highly polar with hydrogen bonds

WATER AS A SOLVENT-HYDROGEN BONDING

Polarity Demonstration

Image used courtesy of CINCH ® Learning

The bond formed between an oxygen atom from one water molecule and a hydrogen atom from another water molecule

Image used courtesy of: http://www.glogster.com/arooke2/hydrogen-bonds/g-6m99vd692fc7hgidt985ta0?old_view=True

Concentration

The concentration of a solution is usually described as concentrated or dilute

There are many ways to express concentration:

Concentration as Percent by Mass

Ratio of the solutes mass to the mass of the solution expressed as a percentage!

Amount of solution = solute + solvent

percent by mass = amount of solute x 100 amount of solution

Concentration as percent by mass

1) What is the percent by mass if 2 grams of sugar is added and dissolved in 10 grams of water?

16.7%

Concentration as percent by mass

2) In order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution?

3.5%

Concentration as MOLARITY

Another common unit of concentration used by chemist is molarity

Molarity = the solutions concentration measured as moles of solute per liter of solutionMolarity = Moles of solute

Liters of solutionUnits of M = Moles / Liter

Concentration as Molarity

1) How much sucrose, in moles, is there in 0.5 liters of a 2-molar (2M) solution?

1 mole

Concentration as Molarity

2) To make a 4.0 M solution, how many moles of solute will be needed if 12 L of solution are required?

Concentration as Molarity

3) 116.88 grams of NaCl are dissolved in 1.5 liters of solution. What is the molarity of this solution?

First, convert grams of NaCl to moles NaCl Found by dividing 116.88g by the molar mass of NaCl,

58.44 g/mol 116.88g NaCl is 2.00 moles of NaCl

Next, divide moles solute by liters of solution 2.00 moles NaCl = 1.33 mol NaCl/L = 1.33 M NaCl

1.5 L

Practice

Try the following calculating concentration as percent by mass and molarity problems

Dilution

What does it mean to dilute a solution?

Dilution

In the lab, sometimes reactions call for different strengths or concentration of solutions in order for a reaction to occur.

We use molarity to create solutions with the proper concentrations.

Often we need to dilute a stronger solution to a weaker one.

DILUTION

Solutions can be diluted simply by adding more solvent and leaving the amount of solute unchanged

What happens to molarity when a solution is diluted? More water has been added, so the total

volume of solution is greater but the amount of solute is the same

Molarity will decrease!

Dilution

We use the following equation to perform dilution calculations:

M1V1=M2V2

M1=Initial molarity

V1= Initial volume

M2= Final molarity

V2=Final volume

DILUTION EXAMPLE1) What would be the resulting molarity of

2.500 L solution when the starting solution had a molarity of 6.00 M and a volume of 417 mL?

M1= 6.00 mol/L M2= ?? V1= 417 mL V2= 2500 mL

M1V1=M2V2

(6.00 mol/L)(417 mL) = (M2)(2500 mL)

(M2) = (6.00 mol/L)(417 mL)

(2500 mL) M2 = 1.00 mol/L

Dilution

2) If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it?

0.19 M (the final volume is 900 mL, set up the equation from that)

STOP

Work on some problems on your own

CONCENTRATION AND SOLUBILITY

The amount of solute affects both solubility and dissolving rate.

A solvent can only dissolve so much solute.

As the concentration increases, the ability to dissolve more decreases, as does the rate at which it will dissolve.

Solution Concentration

Unsaturated When the amount of solute is less than the

maximum that could be dissolved

Saturated When a solution holds the maximum amount of

solute

Fats!

You’ve all heard that we should avoid saturated fats…so what does that mean? Saturated fats (butter, dairy products, meat) are

solid at room temperature and are evenly filled out with hydrogen. They increase the levels of bad cholesterol (LDL) and clog your arteries.

Mono and poly unsaturated fatty acids (corn oil, sunflower oil, and soybean oil, while omega 3 is present in salmon, trout and tuna) remain liquid at room temp and increase the levels of good cholesterol!

Solution Concentration

Supersaturated When a solution holds more than the maximum

amount and is thus unstable!

Supersaturated demohttp://www.youtube.com/watch?v

=1y3bKIOkcmk

SOLUBILITY CURVES

Show the amount of solute that can dissolve in a solvent under normal circumstances at a given temperature

The line for a given element on a set of solubility curves is called the saturation line

Factors affecting Solvation (aka rate of Dissolving)

Solvation: The act of surrounding solute particles with solvent particles to form a solution!

The solute is being pulled apart and surrounded by the solvent. Soluble – if you can dissolve any of the solute Insoluble – if you can’t dissolve any

We can change this by changing many different factors!

Factors Affecting SolvationThe rate at which the solute dissolves in the

solvent (link to KMT) As Kinetic Energy increases, dissolving rate

increases As Kinetic Energy decreases, dissolving rate

decreases As the number of collisions increases, dissolving

rate increases As the number of collisions decreases, dissolving rate

decreases

(1) TEMPERATURE AND DISSOLVING RATE

Increasing the temperature speeds up the movement of its particles

Allows for more collisions between solute particles and solvent particles

(2) SURFACE AREA AND DISSOLVING RATE

Breaking a solid into smaller pieces greatly increases its surface area

More solvent particles can come into contact with more particles of the solute corresponding to increased surface area

Rate of collisions increases as surface area increases

(3) AGITATION AND DISSOLVING RATE

Agitation

Stirring, Mixing, Shaking As agitation speed increases, rate of

dissolving increases As the solvent moves around, more

collisions occur between solvent and solute particles

SUMMARY OF FACTORS AFFECTING DISSOLVING RATESAs temperature ↑, dissolving rate ↑

As particle size ↓, surface area↑, dissolving rate ↑

As agitation ↑, dissolving rate ↑

LAB

Factor’s affecting solubility lab

SOLUTIONS & SATURATIONUnsaturated Saturated Super-

saturatedDefinition More solute can

dissolve in the solvent

No more solute will dissolve in the solvent. If there is extra undissolved solute, it will settle to the bottom of the container.

Under unusual circumstances more solute is dissolved in solvent than it can normally hold

Solubility Curve

Below the saturation line

On the saturation line

Above the saturation line

Can you Dissolve More Solute?

Yes No No, it is already past saturation point

SOLUBILITY CURVE

Let’s practice reading a solubility curve!

FACTORS AFFECTING SOLUBILITY

1. Temperature2. Pressure3. Polarity

FACTORS AFFECTING SOLUBILITY

(1) Temperature Solids and Liquids: Generally, as temperature

increases, the solubility of solids and liquids increases – why?

As temperature ↑, solubility ↑

Gases: Generally, as temperature increases, the solubility of gases decreases – why?

As temperature ↑, solubility ↓

FACTORS AFFECTING SOLUBILITY

(2) Pressure Solids and Liquids: no effect – why?

As pressure ↑, solubility is unaffected

Gases: Generally, as pressure increases, the solubility of gases increases – why?

As pressure ↑, solubility of gases ↑

FACTORS AFFECTING SOLUBILITY(3) Polarity!!

The nature of the solvent affects solubility Like Dissolves Like

Ionic compounds, if they are soluble, dissolve in polar solvents

Polar molecular (covalent) compounds dissolve in polar solvents

Non-polar molecular (covalent) compounds dissolve in non-polar solvents