solutions and solvation

SOLUTIONS AND SOLUTIONS AND SOLVATIONSOLVATION

SOLUTIONS AND SOLUTIONS AND SOLVATIONSOLVATION

The Straight and Narrow Path to The Straight and Narrow Path to SolutionSolution

The Day of Judgement• For You will be tested on 21

February• It is coming, You must be prepared.• You must know your solutions• You must know your Molarity• You must know your way to solve

the problems

MIXTURES VS COMPOUNDS

• Compounds: Chemically combined substances.

• Mixtures: Physically combined substances, normally made up of two or more compounds.

• Heterogeneous: Different Concentrations everywhere. It isn’t the same.

• Homogeneous: Exactly the same concentrations everywhere. It’s all the same everywhere.

SOLVATION• The process of dissolving a solute in a solvent• Solutes: The material that is present in

smaller amounts • Solvents: The material that is present in the

largest amount, can only be one in a solution• And the Solvent said unto the Solute, “Come

and be Dissolved by me!”NaCl(s) Na+(aq) + Cl-(aq)

What can be Solvated• Soluble: The material can be dissolved.• Insoluble: The material can’t be dissolved• Miscible: A liquid that will dissolve• Immiscible: A liquid that will not dissolve• Solubility: How much can dissolve under

the given conditions• Alloy: A metal that is dissolved in

another metal.

Polar in Polar• And the Like Molecules shall be

dissolved by the Like Molecules, Polar unto Polar and Nonpolar unto Nonpolar each Unto it’s own kind

• Unlike Molecules shall not be dissolved by Unlike Molecules, Polar SHALL NOT dissolve Nonpolar, Oil and Water Shall Not dissolve.

Common Polar Solvents• Water: H2O

• Ammonia: NH3

• Ethanol: CH3OH

Water is Polar• As you can see, water has a

positive side and a negative side.

The Process• NaCl goes down into the Water

The Water surrounds the NaCl pulling it apart, Na to the Negative side of water and Cl to the positive side of water and the NaCl is no more, it has been dissolved – it is one with the water. Polar unto Polar.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

NonPolar in NonPolar• The NonPolar molecules become

surrounded by the NonPolar Molecules, LIKE UNTO LIKE, surrounded the Nonpolar Solute is carried away as one with the Nonpolar Solvent.

Common Nonpolar Solvents

• Fats• Oil• Gasoline• Covalent Compounds

Electrolytes versus Nonelectrolytes

• Electrolytes completely break apart and carry an electrical current. Polar

• Nonelectrolytes don’t break apart and don’t carry an electrical current. NonPolar

Like Dissolves Like• Polar substances are dissolved by

Polar Substances• Nonpolar substances are dissolved

by Nonpolar Substances.• Polar does not dissolve Nonpolar.• Nonpolar does not dissolve polar.

Nonpolar will not dissolve in Polar

• Iodine is NonPolar, water is Polar, so it won’t dissolve

• Iodine will dissolve in Carbon Tetra Chloride which is NonPolar.

TYPES OF SOLUTIONS• UNSATURATED: The solution can

dissolve more solute.• SATURATED: The solution cannot

dissolve more solute.• SUPERSATURATED: The solution

has dissolved more solute then it should.

UNSATURATED• More can be added

SATURATED• The Solution cannot dissolve more:

SUPERSATURATED• The solution is holding more then it

should.• When more is added, a lot flows out.

What a Supersaturated Looks Like

• http://www.amazingrust.com/experiments/how_to/Hot-Ice.html

• http://www.wonderhowto.com/how-to-make-sodium-acetate-hot-ice-w-vinegar-baking-soda-274006/

SupersaturatedSupersaturatedSodium Sodium

AcetateAcetate• One application One application of a of a supersaturated supersaturated solution is the solution is the sodium acetate sodium acetate “heat pack“heat pack.”.”

SUPERSATURATED• HOW IT HAPPENS• As a general rule: Solvents can hold a certain

amount of Solute at a certain temperature• If the temperature is raised, more solute can

be dissolved.• If the solution is then cooled, the solute stays

dissolved.• The solution is holding more solute then it

should.

How solutions are measured

• Concentration: How much solute there is in a given amount of Solvent.

• Molarity: Moles solute/Liters solution• Molality: Moles solute/Kilograms

solvent• Mass Percent: grams solute/grams

solution

Concentration of Concentration of SoluteSolute

Concentration of Concentration of SoluteSolute

The amount of solute in a The amount of solute in a solution is given by its solution is given by its concentrationconcentration.

Molarity (M) = moles soluteliters of solution

Properties of solutions• Colligative property: A property

that changes as a result of the solution being made

• Vapor Pressure Lowering: The vapor pressure of the solution goes down, the amount of substance release into the air goes down.

More properties of solutions

• Boiling Point elevation: Boiling point of a solution is higher then that of just the solvent.

• Freezing Point depression: Freezing point of a solution is lower then that of just the solvent.

• Electrolyte: A substance in a solution that allows the solution to transmit an electric current

Some DefinitionsSome DefinitionsA solution is a mixture A solution is a mixture

of 2 or more of 2 or more substances in a substances in a single phase. single phase.

One constituent is One constituent is usually regarded as usually regarded as the the SOLVENTSOLVENT and and the others as the others as SOLUTESSOLUTES..

Parts of a Solution• SOLUTE – the part

of a solution that is being dissolved (usually the lesser amount)

• SOLVENT – the part of a solution that dissolves the solute (usually the greater amount)

• Solute + Solvent = Solution

Solute

Solvent

Example

solid

solid Brass

solid

liquid

Tea, Coffee

gas solid Foamliquid

liquid

Ammonia

gas liquid

Carbonated Water

gas gas Air

IONIC COMPOUNDSIONIC COMPOUNDSCompounds in Aqueous SolutionCompounds in Aqueous Solution

Many reactions involve ionic Many reactions involve ionic compounds, especially reactions in compounds, especially reactions in water — water — aqueous solutions.aqueous solutions.

KMnOKMnO44 in water in water KK++(aq) + MnO(aq) + MnO44--(aq)(aq)

How do we know ions are How do we know ions are present in aqueous present in aqueous solutions?solutions?

The solutions conduct The solutions conduct electricityelectricity

They are called They are called ELECTROLYTESELECTROLYTES

HCl, MgClHCl, MgCl22, and NaCl are , and NaCl are strong electrolytes. strong electrolytes. They They dissociate completely (or dissociate completely (or nearly so) into ions.nearly so) into ions.

Aqueous SolutionsAqueous Solutions

Aqueous Aqueous SolutionsSolutions

Some compounds Some compounds dissolve in water but dissolve in water but do not conduct do not conduct electricity. They are electricity. They are called called nonelectrolytes.nonelectrolytes.

Examples include:Examples include:sugarsugarethanolethanolethylene glycolethylene glycol

Examples include:Examples include:sugarsugarethanolethanolethylene glycolethylene glycol

PROBLEM: Dissolve 5.00 g of NiClPROBLEM: Dissolve 5.00 g of NiCl22•6 •6 HH22O in enough water to make 250 O in enough water to make 250 mL of solution. Calculate the mL of solution. Calculate the Molarity.Molarity.

PROBLEM: Dissolve 5.00 g of NiClPROBLEM: Dissolve 5.00 g of NiCl22•6 •6 HH22O in enough water to make 250 O in enough water to make 250 mL of solution. Calculate the mL of solution. Calculate the Molarity.Molarity.

Step 1: Step 1: Calculate moles Calculate moles of NiClof NiCl22•6H•6H22OO

5.00 g • 1 mol

237.7 g = 0.0210 mol

0.0210 mol0.250 L

= 0.0841 M

Step 2: Step 2: Calculate MolarityCalculate Molarity

[NiClNiCl22•6 H•6 H22OO ] = 0.0841 M

Step 1: Step 1: Change mL to L.Change mL to L.

250 mL * 1L/1000mL = 0.250 L250 mL * 1L/1000mL = 0.250 L

Step 2: Step 2: Calculate.Calculate.

Moles = (0.0500 mol/L) (0.250 L) = 0.0125 molesMoles = (0.0500 mol/L) (0.250 L) = 0.0125 moles

Step 3: Step 3: Convert moles to grams.Convert moles to grams.

(0.0125 mol)(90.00 g/mol) = (0.0125 mol)(90.00 g/mol) = 1.13 g1.13 g

USING MOLARITYUSING MOLARITYUSING MOLARITYUSING MOLARITY

moles = M•Vmoles = M•V

What mass of oxalic acid, What mass of oxalic acid, HH22CC22OO44, is, is

required to make 250. mL of a 0.0500 Mrequired to make 250. mL of a 0.0500 Msolution?solution?

Learning Check

How many grams of NaOH are required to prepare 400. mL of 3.0 M NaOH solution?

1) 12 g2) 48 g3) 300 g

Two Other Concentration Two Other Concentration UnitsUnits

grams solutegrams solutegrams solutiongrams solution

MOLALITY, mMOLALITY, m

% by mass% by mass = =

% by mass% by mass

m of solution = mol solute

kilograms solvent

Calculating Calculating ConcentrationsConcentrations

Calculate molalityCalculate molality

Calculate molalityCalculate molality

Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g

of Hof H22O. Calculate m & % of ethylene glycol (by mass).O. Calculate m & % of ethylene glycol (by mass).

Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g

of Hof H22O. Calculate m & % of ethylene glycol (by mass).O. Calculate m & % of ethylene glycol (by mass).

conc (molality) = 1.00 mol glycol0.250 kg H2O

4.00 molalconc (molality) = 1.00 mol glycol0.250 kg H2O

4.00 molal

%glycol = 62.1 g

62.1 g + 250. g x 100% = 19.9%%glycol =

62.1 g62.1 g + 250. g

x 100% = 19.9%

Calculate weight %Calculate weight %

Learning Check

A solution contains 15 g Na2CO3 and

235 g of H2O? What is the mass %

of the solution? 1) 15% Na2CO3

2) 6.4% Na2CO3

3) 6.0% Na2CO3

Dilutions• Stock Solution: A solution of

known concentration, normally saturated, used to make other solutions.

• Diluting: Adding solvent to make a reduce the concentration of a solution.

Dilution Equation• M1V1 = M2V2

• Mr Simms needs 250 mL of 0.150 M CuCl2 Solution. He has 3.00 M Stock Solution. How much of the stock solution does he need to use?

Problem Set up• M1V1 = M2V2

• M1 = 0.150 M

• V1 = 250 mL

• M2 = 3.00 M

• V2 = X mL

Answer• (0.150 M)(250 mL) = (3.00 M)X• (0.150 M)(250 mL) = X• (3.00 M)• X = 12.5 mL• Explanation: I need to start with 12.5

mL of 3.00M Stock Solution and dilute it to 250 mL by adding 237.5 mL of Water.

Boiling Point Elevation T = (# ions)(molality)Kb

T = Change in Temperature, not new Temperature

• (# ions) = Number of ions, NaCl has 2, MgCl2 = 3, All Covalent compounds are 1.

• Molality = You should know this already

• Kb = a Boiling point constant for the Solvent

Example• What is the new boiling point for a

1.20 molal solution of NaI?T = (# ions)(molality)Kb

• # ions = 2• Molality = 1.20 molal

• Kb for water = 0.512 C/m

Example continuedT = (# ions)(molality)Kb

T = (2)(1.20)(0.512)T = 1.23 C

• Old Boiling point = 100

• New Boiling point = 101.23

Freezing Point Depression

• What would the new Freezing point of the solution be?

T = (# ions)(molality)Kf

• Kf for water is 1.86 C/m T = (2 ions)(1.2 m)(1.86 C/m) T = 4.46 C• Old Freezing point of water = 0• New Freezing point of water = 0 – 4.46 = -4.46 C