UNIT 8, PART I - SOLUTIONS AND SOLUBILITY

KEY TERMS

Anion - A negatively charged ion

Aqueous Solution - A solution where water is mixed with something to make a solvent

Cation - A positively charged ion

Concentration - The amount of solute per unit volume of solution Dilution - Weakening or reducing the concentration Molarity (M) - Concentration measured by the number of moles of solute per liter of solution Insoluble - Incapable of being dissolved

Polarity - A separation of electric charge leading to a molecule having an electric dipole Saturated Solution - A solution that contains the maximum amount of solute at a given

temperature

KEY TERMS

Solubility - The quantity of a particular substance that can dissolve in a particular solvent

Solubility Curve - A graph showing the relationship between solubility and temperature

Soluble - Able to be dissolved

Solute - The dissolved matter in a solution

Solvent - Able to dissolve other substances Unsaturated Solution - A solution that contains less than the

maximum amount of solute at a given temperature

WATER AS A SOLVENT

Water is the most effective solvent

Water 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 Used courtesy of: http://www.volusia.org/services/public-works/water-resources-and-utilities/

WATER AS A SOLVENT – POLARITY (IT IS THE KEY)

Image used courtesy of: http://www.ecfs.org/projects/prepole/MARINE%20BIOLOGY%2012/Chapter%20Readings/Ch%201%20Oceanography/Chapter%201%20Notes.htm

WATER AS A SOLVENT- HYDROGEN BONDING

Image used courtesy of CINCH ® Learning

The powerful attraction 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

SOLUBILITY

The ability to dissolve a solute in a solvent to form a solution, a homogeneous mixture

Solute – The matter dissolved in a solvent

Solvent – The matter in which a solute is dissolved

Solution – Homogeneous mixture

TYPES OF SOLUTIONS

FACTORS AFFECTING SOLUBILITY

It is all about 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

FACTORS AFFECTING SOLUBILITY

Factors affecting the solubility of solids and liquids Temperature

Generally, as temperature increases, the solubility of solids and liquids increases

Factors affecting the solubility of gases Temperature

Generally, as temperature increases, the solubility of gases decreases

Pressure

Generally, as pressure increases, the solubility of gases increases

SUMMARY OF FACTORS AFFECTING SOLUBILITY

Temperature

As temperature ↑, solubility of liquids and solids↑

As temperature ↑, solubility of gases↓

Pressure

As pressure ↑, solubility of liquids and solids is unaffected

As pressure ↑, solubility of gases ↑

 

SUMMARY OF FACTORS AFFECTING SOLUBILITY

Nature of Solvent Generally the nature of the solvent will determine what kinds

of matter will dissolve in it. Polar solvents (such as water) will generally dissolve polar compounds.

Non‐polar compounds will generally dissolve non‐polar compounds.

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

LIKE DISSOLVES LIKE!

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

DISSOLVING RATE

The rate at which the solute dissolves in the solvent

As Kinetic Energy increases, dissolving rate increasesAs Kinetic Energy decreases, dissolving rate decreases

As the number of collisions increases, dissolving rate increases

As the number of collisions decreases, dissolving rate decreases

DISSOLVING RATE

Factors affecting dissolving rateTemperature

As temperature increases, dissolving rate increases

Surface Area As surface area increases, particle size decreases As surface area increases, dissolving rate increases

Agitation As agitation increases, dissolving rate increases

TEMPERATURE AND DISSOLVING RATE

Since temperature is a measurement of the average kinetic energy, changing the temperature by adding or removing heat will change the rate of dissolving. Increasing the temperature speeds up the movement of its particles

The change in temperature will affect both the number of collisions and the probability that as particles collide the solute will dissolve in the solvent. Allows for more collisions between solute particles and solvent particles

Used courtesy of: http://www.seriouseats.com/2012/10/ask-the-food-lab-on-hot-chocolate-and-whole-wheat.html

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

AGITATION AND DISSOLVING RATE

Agitation is the result of an external force causing the motion of the solute and the solvent such that there is an increased chance of collision.

Stirring, Mixing, Shaking

As agitation speed increases, rate of dissolving increases

As the solvent moves around, more collisions occur between solvent and solute particles

Used courtesy of: http://www.pennlive.com/lehighvalley-generalent/index.ssf/2008/06/in_defense_of_koolaid.html

SUMMARY OF FACTORS AFFECTING DISSOLVING RATES

As temperature ↑, dissolving rate ↑

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

As agitation ↑, dissolving rate ↑

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 rate at which it will dissolve decreases.

CONCENTRATION OF SOLUTIONS Concentration – the degree to which a solution contains the maximum

amount of solute.

Directly related to density

Qualitative

Uses terms saturated and unsaturated to reference the amount of solute dissolved in the solvent

Quantitative

Molarity – the number of moles dissolved in one liter of solution

SOLUTIONS AND SATURATION• Saturated Solution – A solution is considered saturated when it contains the

maximum amount of solute given the volume and environmental conditions of the solvent.

• Unsaturated Solution – Any solution into which more solute can be dissolved is unsaturated. • An unsaturated solution that is close to the point of saturation is referred to as

“concentrated”.• An unsaturated solution well below the point of saturation is referred to as “dilute”.

• Super‐Saturated Solution – Any solution that contains more dissolved solute than it could contain under normal conditions is super‐saturated. • A beverage with carbonated water is a supersaturated solution. It is packaged into

cans or bottles under conditions of high pressure. When the can or bottle is later opened, the carbon dioxide bubbles out of solution under the lower pressure.

• Rock candy is made using a supersaturated solution of sugar and allowing the sugar crystals to slowly form on a string dipped in sugar.

SOLUTIONS & SATURATION

Unsaturated Saturated Supersaturated

Definition Contains less than the maximum amount of solute. More solute can dissolve in the solvent

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

Contains more dissolved solute than the maximum under normal conditions

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

Imaged used courtesy of: http://www.mts.net/~alou/Chemistry%2011/Unit%204%20-%20Solutions%20Lessons/Lesson%203%20-%20Factors%20Affecting%20Solubility.htm

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

Comparisons are made using the line for a given compound Under the curve – the solution is unsaturated Above the curve without excess – the solution is supersaturated Above the curve with excess – the solution is saturated On the curve – the solution is saturated

SOLUBILITY CURVES

QUANTITATIVE SOLUBILITY: MOLARITY

Measured as moles of solute per liter of solution

Molarity = Moles of solute Liters of solution

M = Moles Liter

MOLARITY EXAMPLE

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/mol116.88g 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

DILUTION What does it mean to dilute a solution? Solutions can be diluted simply by adding water 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!

We use the following equation to perform dilution calculations:M1V1=M2V2

M1=Initial molarity

V1= Initial volume

M2= Final molarity

V2=Final volume

DILUTION EXAMPLE What would be the resulting molarity of 2.5 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

DISSOCIATION AND DISPERSION

Dissociation – When ionic compounds dissolve, they separate into the ions that were bonded together.

Example: Potassium sulfate will dissociate into potassium ions and sulfate ions. K2SO4 → 2K1+ + SO4

2-

More examples of dissociation: NaCl → Na1+ + Cl 1-

MgCl2 → Mg2+ + 2 Cl1-

Al2(SO4)3 → 2 Al3+ + 3SO42-

Dispersion – When complete dispersion occurs, the molecules of the solute are uniformly mixed with the molecules of the solvent. This occurs with covalent compounds.

ELECTROLYTIC SOLUTIONS

Electrolytic solutions conduct an electrical current

Ions dissociate when dissolved in water

Ions, because they are charged particles, act as a path for the flow of electricity

The more ions present, the more electrolytic the solution is

Non-electrolytic solutions do not conduct an electrical current

ELECTROLYTIC SOLUTIONS

Soluble Ionic Solute

Non-Soluble Ionic Solute

Non-Soluble Covalent Solute

Electrolyte Yes No No

CONTROLLING ELECTROLYTIC SOLUTIONS

In order to increase the electrolytic properties of a solution you must increase the concentration of ions present in the solution

Reduce the volume of the solution while maintaining the amount of electrolytic solute

Increase the amount of electrolytic solute without modifying the volume

Using a different electrolytic solute which produces more ions when it dissociates

In order to decrease the electrolytic properties of a solution you must decrease the concentration of ions present in the solution

Dilute the electrolytic solution

Using a different electrolytic solute which produces less ions when it dissociates