Solutions

What is a solution?  A homogenous mixture of two or more substances uniformly dispersed throughout a single phase.  Suspension: a mixture in which the particles of material are more or less evenly dispersed through out a liquid or a gas.  Colloid: a mixture containing of tiny particles that are intermediate in size between those in solutions and those in suspensions and is suspended in a liquid, solid or gas.

Solubility & Polarity  Solubility : is the ability of one substance to dissolve in another at a given temperature and pressure.  Ex: paint/ paint thinner (nonpolar) Oil/ water ( polar/ nonpolar). So polar dissolves in polar and nonpolar dissolves in nonpolar.  Solvent  Solute

How to separate mixtures  Filtration  Centrifuge  Chromatography  Distillation

Vitamin C water soluble or not??  Can the human body make its own vitamin C?  Can vitamin C be stored in the body?  Disease scurvy??  Function of vitamin C? synthesis of collagen, a protein that makes up tendons and enables muscle movement.

Vitamin A  Must be obtained in food and especially yellow vegetables  Needed for respiratory tracts, skin, bone growth and eyes.  Has a long nonpolar carbon hydrogen chain, so its very low in solubilty in water, but soluble in oil and fat.  So much vitamin A can accumulate in the fat and eventually become toxic.

THE RULE “ LIKE DISSOLVES LIKE”  NONPOLAR : BONDS are LONDON forces of attraction between molecules. That’s why they are very soluble with each other.  Miscible : liquids that are able to dissolve in each other.  Immiscible : two or more liquids that don’t mix together

How can we increase solubility's of solids  Greater surface area- dissolving takes place at the surface where solute and solvent molecules are in contact. - Breaking the solid into smaller pieces

 Increasing Temperature: an increases in temperature is effective because solvent molecules with greater kinetic energy can dissolve more solute particles.  Pressure has little affect on solubility

Solubility rules Acetates, CH3CO2- : EXCEPT THAT OF Fe 3+ Alkali Metals : group 1, except LiF Ammonium, NH 4 Bomides, Br-, except those of Ag, Pb, Hg 2 Cholrides, Cl-, except those of Ag, Pb, Hg 2 Nitrates, NO 3 Sulfates SO4, except those of Ca, Sr, Ba, Pb, Hg 2

Saturation/ unsaturated  Any solution that cannot dissolve anymore solute under the goiven conditions  Unsaturated solution: A solution that contains less Solute that a saturated solution And its able to dissolve addititional

Hand Warmers and the concept of Supersaturation Your assignment is to make a hand warmer and explain how diapers work!!! Due Friday

Solubility Equilibrium The physical state in which the opposing process of dissolution and crystilization of a solute occur at equal rates. Particles of solute in solution = excess solute

Can Gases Dissolve in Liquids? GIVE AN EXAMPLE…

Gas Solubility Depends on Pressure and Temp. Henry’s Law: at constant temp, the solubility of agas in a liquid is directly proportional to the partial pressure of the gas on the surface of the liquid.

Physical Properties in Solutions  Electrical Conductivity: The conductivity of a substance depends on whether it contains charged particles and the particles must be able to move. Question: Does NaCl conduct electricity?? And why?Does pure water conduct electricity? Why? Does rain water conduct electricity? Does ocean or tap water conduct electricity?

ELECTROLYTES A substance that dissolves in water to give a solution that conducts an electric current Strong electrolytes: completely Dissociates into ions and conduct electricity. Weak electrolytes: provides few ions in a solution

Electrolytes can be:  Salts  Acids  Bases Because they all have ions when dissolved!!!

Acids Acid reacts with water to form Hydronium Ion H3O – which is made of a proton combined with water!!

Colligative Properties It’s the Physical effect of the solute on the solvent. The degree of effect depends on the number of particles in a certain mass of solvent. The greater the particle concentration the greater the boiling elevation or freezing depression.

Colligative properties are all caused by:  Decrease in vapor pressure of the solvent, due to fewer solvent particles and more solute. So fewer solvent particles are their to vaporize.  Boiling point rises: that happens when the liquids vapor pressure is equal to the atmospheric pressure above the liquid.  Freezing points lowers: point at which water and ice are in equilibrium.  Osmotic pressure is higher All the above depend on molality of solution.

27 Change in Freezing Point The freezing point of a solution is LOWER than that of the pure solvent Pure water Ethylene glycol/water solution

28 Boiling Point Elevation and Freezing Point Depression ∆T = Kmi ∆T = Kmi SubstanceKbKb benzene2.53 camphor5.95 carbon tetrachloride5.03 ethyl ether2.02 water0.52 m = molality K = molal freezing point/boiling point constant SubstanceKfKf benzene5.12 camphor40. carbon tetrachloride30. ethyl ether1.79 water1.86

29 Change in Boiling Point Dissolve 62.1 g of glycol (1.00 mol) in 250. g of water. What is the boiling point of the solution? K b = 0.52 o C/molal for water (see K b table). Solution∆T BP = K b m i 1.Calculate solution molality = 4.00 m 2.∆T BP = K b m i ∆T BP = 0.52 o C/molal (4.00 molal) (1) ∆T BP = 0.52 o C/molal (4.00 molal) (1) ∆T BP = 2.08 o C BP = = o C (water normally boils at 100)

30 Calculate the Freezing Point of a 4.00 molal glycol/water solution. K f = 1.86 o C/molal (See K f table) Solution ∆T FP = K f m i = (1.86 o C/molal)(4.00 m)(1) = (1.86 o C/molal)(4.00 m)(1) ∆T FP = 7.44 FP = 0 – 7.44 = o C (because water normally freezes at 0) Freezing Point Depression

31 At what temperature will a 5.4 molal solution of NaCl freeze? Solution ∆T FP = K f m i ∆T FP = (1.86 o C/molal) 5.4 m 2 ∆T FP = (1.86 o C/molal) 5.4 m 2 ∆T FP = 20.1 o C ∆T FP = 20.1 o C FP = 0 – 20.1 = o C FP = 0 – 20.1 = o C Freezing Point Depression

Surfactants Have you tried to wash your hands when they were very dirty without using soap? What happens? Does it work? Why?

Heads up!!  Prespiration contains water and oil  Water evaporates, but oil remains behind and coats the dirty particles.  Water and oil don’t mix so washing without soap is not successful…. WHY SOAP?? Soap molecules contain long nonpolar hydrocarbon chains which are soluble in nonpolar oil, and a negative charged end with is soluble in water.

Surfactant A compound that concentrates at the boundry surface between two immiscible phases, solid/ liquid and liquid/liquid and liquid/gas

36 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

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

38 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?

39 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

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

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

42 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 %

43 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

44 Using mass % How many grams of NaCl are needed to prepare 250 g of a 10.0% (by mass) NaCl solution?

45 Review Colligative Properties On adding a solute to a solvent, the properties of the solvent are modified. Vapor pressure decreasesVapor pressure decreases Melting point decreasesMelting point decreases Boiling point increasesBoiling point increases Osmosis is possible (osmotic pressure)Osmosis is possible (osmotic pressure) These changes are called COLLIGATIVE PROPERTIES. They depend only on the NUMBER of solute particles relative to solvent particles, not on the KIND of solute particles.