Solutions Dr. Muon Hazlett Mandeville High School

Solutions (solns) Definition: – It is a homogeneous mixture – It is made up of a solute (what is being dissolved) and a solvent (what the solute is dissolved in) Solute + Solvent = Solution – It can be a gas, liquid, or a solid or even a combination of these phases – It does not separate into its parts on its own

Solubility If a solute dissolves in a solvent, it is soluble – Solubility affected by Temperature, Pressure, Agitation, etc. The process in which the solvent particles surround the solute and “cause” it to dissolve is called solvation – If this occurs in water – called hydration – Rule of Solvation – “Like Dissolves Like”

Rule of Solvation – “Like Dissolves Like” Refers to polar solutes dissolving in polar solvent, but not in nonpolar solvents This is due to the charges found on the molecules and opposite charges attracting each other If it does mix – said to be miscible, and if doesn’t – immiscible – Immiscible mixtures are not solutions since they will filter or separate on their own – Like oil and water

If the solute is an ionic compound and is dissolving completely, it is breaking down into its cations and anions – This is called ionization – Dependent upon the dissociation energy (D o ), the energy needed to break apart the ionic compound – This is a part of the solvation process

Saturation Saturation refers to the level of solute in the solvent If the solvent can not dissolve any more solute, then the two are in equilibrium and the solution is saturated If the solute “falls” out of the solvent – oversaturation If not enough solute - undersaturated

Solution Types Suspension - the solute will filter out of the solvent on its own (dirt in water) Thixotrope - the solute and solvent adt as a solid until agitated, then it acts as a liquid Emulsion - a liquid with a solid solute dissolved in it Aerosol - a colloid using a gas as a propellant Colloid - a heterogeneous mixture, the solute does not settle from solvent

Colligative Properties of Solns Properties of solns that depend on the number of solute particles in the solvent 1.Vapor Pressure – affecting evaporation rates. This is amount of solvent found in gas phase above the solution. Lowers vapor pressure. 2.Boiling Point – more solute, higher the B p 3.Freezing Point – more solute, lower F p 4.Osmotic Pressure – affects the passing through of semi-permeable membranes

Concentration [C] Concentration symbolized by brackets [ ] Refers to amount of solute in the solvent Common measures are ppm (parts per million) or ppb (parts per billion)

Concentration Formula General: 1.C = mass of solute mass of soln 2.% C = mass of solute x 100 mass of soln 3.C ppm = mass of solute x 10 6 mass of soln

4. mass soln = mass of solute C 5. mass solute = C x mass solvent (1 - C) 6. Soln = solute + solvent 7. Volume % = vol. solute x 100 vol. soln

Molarity (M) Gives the number of moles of solute per liter of soln M = mols of solute = (n) liters of soln V *Remember  n = mass/molar mass

Molality (m) Gives the number of mols of solute per kg of solvent m = mols solute = n kg solvent kg *Remember – 1 L = 1 kg 1 ml = 1 g = 1 cm 3

Dilution Mixing one substance into another to lower the concentration levels M 1 V 1 = M 2 V 2 Molarity x Volume initial = Molarity x Volume final Rearrange the formula to determine individual variables For multiple solns: – (M 1 V 1 ) + (M 2 V 2 ) = M diluted soln V diluted soln

Mole Fraction Ratio of mols of solute or solvent to the total number of mols in soln – X A = solvent mol fraction = n A __ n A + n B X B = solute mol fraction = ___n B __ n A + n B

Calculating Colligative Properties Vapor Pressure Lowering: Δ P V = X B P A ◦ Where Δ P V is change in vapor pressure; X B is solute mol fraction; and P A ◦ is vapor pressure of pure solvent found in a reference source like the CRC

Boiling Point Elevation: Δ B P = i K B m  Where i is the van’t Hoff constant; K B is the boiling constant from a reference source (H 2 O is 0.513); and m is the molality of the solution  The van’t Hoff constant is the degree of dissociation for a substance (the number of parts it breaks into) and we can use 2 if an ionic compound, 1 if it is covalent

Freezing Point Depression: Δ F P = i K f m Where i is van’t Hoff constant; F P is freezing point constant of pure solvent (with no solute in it), (H 2 0 is 1.86); and m is molality of solution

Osmotic Pressure (Π) Π = i M R T Where i is van’t Hoff constant; M is the molar concentration; R is the gas constant ( L atm/mol K); and T is temperature in Kelvin

Henry’s Law For a gas dissolved in a solution At a constant T, amt. of gas dissolved in a liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid  S 1 = S 2 P 1 P 2  Where S is initial and final solubility in g per L; and P is initial and final pressure usually in atmospheres (atm)