SOLUTIONS AND SOLVATION The Straight and Narrow Path to Solution

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: H 2 O Ammonia: NH 3 Ethanol: CH 3 OH

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. f

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.

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Supersaturated Sodium Acetate Supersaturated Sodium Acetate One application of a supersaturated solution is the sodium acetate “heat pack.”One application of a supersaturated solution is the sodium acetate “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 Solute The amount of solute in a solution is given by its concentration The amount of solute in a solution is given by its concentration. Molarity (M) = moles solute liters 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 Definitions A solution is a mixture of 2 or more substances in a single phase. One constituent is usually regarded as the SOLVENT and the others as SOLUTES.

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 Solut e Solven t Example solid Brass solidliquidTea, Coffee gassolidFoam liquid Ammonia gasliquid Carbonated Water gas Air

IONIC COMPOUNDS Compounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. KMnO 4 in water K + (aq) + MnO 4 - (aq)

How do we know ions are present in aqueous solutions? The solutions conduct electricity They are called ELECTROLYTES HCl, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. Aqueous Solutions

Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugarethanol ethylene glycol Examples include: sugarethanol ethylene glycol

PROBLEM: Dissolve 5.00 g of NiCl 2 6 H 2 O in enough water to make 250 mL of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl 2 6H 2 O Step 2: Calculate Molarity NiCl 2 6 H 2 O [NiCl 2 6 H 2 O ] = M

Step 1: Change mL to L. 250 mL * 1L/1000mL = L Step 2: Calculate. Moles = ( mol/L) (0.250 L) = moles Step 3: Convert moles to grams. ( mol)(90.00 g/mol) = 1.13 g USING MOLARITY moles = MV What mass of oxalic acid, H 2 C 2 O 4, is required to make 250. mL of a M solution?

Learning Check How many grams of NaOH are required to prepare 400. mL of 3.0 M NaOH solution? 1)12 g 2)48 g 3) 300 g

Two Other Concentration Units grams solute grams solution MOLALITY, m % by mass = % by mass m of solution= mol solute kilograms solvent

Calculating Concentrations Calculate molality Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H 2 O. Calculate m & % of ethylene glycol (by mass). Calculate weight %

Learning Check A solution contains 15 g Na 2 CO 3 and 235 g of H 2 O? What is the mass % of the solution? 1) 15% Na 2 CO 3 2) 6.4% Na 2 CO 3 3) 6.0% Na 2 CO 3

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 M 1 V 1 = M 2 V 2 Mr Simms needs 250 mL of M CuCl 2 Solution. He has 3.00 M Stock Solution. How much of the stock solution does he need to use?

Problem Set up M 1 V 1 = M 2 V 2 M 1 = M V 1 = 250 mL M 2 = 3.00 M V 2 = 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 mL of Water.

Boiling Point Elevation  T = (# ions)(molality)K b  T = Change in Temperature, not new Temperature (# ions) = Number of ions, NaCl has 2, MgCl 2 = 3, All Covalent compounds are 1. Molality = You should know this already K b = 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)K b # ions = 2 Molality = 1.20 molal K b for water = C/m

Example continued  T = (# ions)(molality)K b  T = (2)(1.20)(0.512)  T = 1.23 C Old Boiling point = 100 New Boiling point =

Freezing Point Depression What would the new Freezing point of the solution be?  T = (# ions)(molality)K f K f 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 = C