Physical Properties of Solutions Review and Colligative Properties

Physical Properties of Solutions Review andColligative Properties

Solutions Why does a raw egg swell or shrink when placed in different solutions?

solutions A solution is a HOMOGENEOUSmixture of 2 or more substances in a single phase. One part is regarded as the SOLVENTand the other is the SOLUTES.

Parts of a Solution • SOLUTE –part of a solution that is being dissolved (usually the lesser amount) • SOLVENT – part of a solution that dissolves the solute (usually the greater amount) • Solute + Solvent = Solution

Definitions Solutions can be classified as saturated or unsaturated. A saturated solution contains the maximum quantity of solute that dissolves at that temperature. An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

Example: Saturated and Unsaturated Fats Saturated fats = saturated because all of the bonds between the carbon atoms in a fat are single bonds. So… bonds on the carbon are“saturated” with hydrogen. These are stable and hard to break apart. The body can only use these for energy, and so the excess is stored. Sooooo… these should be avoided in diets. From= sheep and cattle fats. Butter and coconut oil are mostly saturated fats. Unsaturated fats have at least one double bond between carbon atoms; • monounsaturated = one double bond, • polysaturated = more than one double bond. • So.. bonds are broken easily, chemically changed, and used for a variety of purposes. These are REQUIRED to carry out many functions in the body. Fish oils (fats) are usually unsaturated. Game animals (chicken, deer) are usually less saturated, but not as much as fish. Olive and canola oil are monounsaturated.

Definitions SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved Supersaturated solutions are unstable. supersaturation is temporary Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate.

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

solubility increases with increasing temperature solubility decreases with increasing temperature Temperature and Solubility Solid solubility and temperature

Temperature and Solubility Gas solubility and temperature solubility usually decreases with increasing temperature

low P high P low c high c Pressure and Solubility of Gases Solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law). c is the concentration (M) of the dissolved gas c = kP P is the pressure of the gas over the solution k is a constant (mol/L•atm) that depends only on temperature

Three types of interactions in the solution process: • solvent-solventinteraction • solute-soluteinteraction • solvent-solute interaction DHsoln = DH1 + DH2 + DH3

A colloid = dispersion of particles of one substance throughout a dispersing medium of another substance. • Colloidversus solution • collodial particles are much larger than solute molecules • collodial suspension is not as homogeneous as a solution

K+(aq) + MnO4-(aq) IONIC COMPOUNDSCompounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. KMnO4 in water

Aqueous Solutions How do we know ions are present in aqueous solutions? Solutions conduct electricity! Called ELECTROLYTES HCl, MgCl2, 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: sugar ethanol ethylene glycol

It’s Time to Play Everyone’s Favorite Game Show… Electrolyte or Nonelectrolyte! NO YES

Electrolyte Solutions 0.1 m NaCl solution 0.1 mNa+ ions & 0.1 mCl- ions Colligative properties =properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 m NaCl solution 0.2 m ions in solution factors (i) 2 NaCl CaCl2 3 C6H12O6 Nonelectrolytes Organic compounds 1

Electrolytes in the Body • Carry messages to and from the brain as electrical signals • Maintain cellular function with the correct concentrations electrolytes

“like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other. • polar molecules are soluble in polar solvents • C2H5OH in H2O • non-polar molecules are soluble in non-polar solvents • CCl4in C6H6 • ionic compounds are more soluble in polar solvents • NaCl in H2O or NH3 (l) • polar molecules are NOT soluble in nonpolar molecules

Styrofoam + water Nonpolar vs polar 2. Styrofoam + acetone nonpolar vs nonpolar 3. Starch peanuts + acetonepolar vs nonpolar 4. Starch peanuts + water polar vs polar

x 100% mass of solute x 100% = mass of solution mass of solute mass of solute + mass of solvent Concentration Units The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. Percent by Mass % by mass =

moles of solute liters of solution moles of solute m = mass of solvent (kg) M = Concentration Units Molarity(M) Molality(m)

moles solute ( M ) = Molarity liters of solution Concentration of Solute The amount of solute in a solution is given by its concentration.

How to REMEMBER hint: Molarity = M CapitalM -r……Liters Mr.Do you want something todrink?? (liters)

1.0 L of water was used to make 1.0 L of solution. Notice the water left over.

PROBLEM: Dissolve 5.00 g of NiCl2•6 H2O in enough water to make 250 mL of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl2•6H2O Step 2: Calculate Molarity [NiCl2•6 H2O] = 0.0841 M

USING MOLARITY What mass of oxalic acid, H2C2O4, is required to make 250. mL of a 0.0500 M solution? Step 1: Change mL to L. 250 mL * 1L/1000mL = 0.250 L Step 2: Calculate. Moles = (0.0500 mol/L) (0.250 L) = 0.0125 moles Step 3: Convert moles to grams. (0.0125 mol)(90.00 g/mol) = 1.13 g moles = M•V

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

Solution M = moles of solute Liters of solution M * V = moles 3.0 mol/L * 0.400 L = 1.2 mol NaOH 1.2 mole NaOH x 40.0 g NaOH 1 mole NaOH = 48 g NaOH

Concentration Units An IDEAL SOLUTION = properties depend only on the concentration of solute. Need concentration units to tell the number of solute particles per solvent particle. The unit “molarity” does not do this!

mol solute m of solution = kilograms solvent Two Other Concentration Units MOLALITY, m % by mass grams solute grams solution % by mass = X 100%

How to REMEMBER hint: Molality = m Little l = little m Little Kid (kg)

Calculating Concentrations Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H2O. Calculate molality and % by mass of ethylene glycol.

Calculating Concentrations Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H2O. Calculate m & % of ethylene glycol (by mass). Calculate molality Calculate weight %

Colligative Properties properties of a solution that differ from the properties of a pure solvent due to the number of particles dissolved in a given mass of solution(affect of solute on solvent is due to the number of particles) • Decrease in vapor pressure • Boiling point elevationRaising the Boiling Point • Freezing point depression Lowering the freezing Point • Osmotic pressure

Colligative Properties On adding a solute to a solvent, the properties of the solvent are modified. • Vapor pressure decreases • Melting point decreases • Boiling point increases • Osmosis is possible (osmotic pressure) These changes are called COLLIGATIVE PROPERTIES. Properties caused by a difference in the NUMBER of solute particles dissolved in a given solution. not on the KIND of solute particles.

A. Decrease in Vapor Pressure • Decrease in vaporpressureis proportional to the number of particles the solute makes in solution • This makes the B.P. go up • Solute causes the vapor pressure or solvent to decrease. • Since BP is the temperature at which the vapor pressure of the liquid is equal to the pressure on the liquid, • the boiling point of the solution is higher than the boiling point of the pure solvent according to the equation:

On surface of the pure solvent there are more solvent molecules at the surface than in the right-hand solution flask. • So, it is more likely that solvent molecules escape into the gas phase on the left than on the right. • Therefore, the solution should have a lower vapor pressure than the pure solvent. Why add SALT to a boiling pot? • Increase BP to cook at High Temperatures • Why?? Keep nutrients from cooking too long in hotter pot (faster)

B.Boiling Point Elevation • difference in temperature between Boiling point of a solution and that of pure solvent • Because of decreased vapor pressure, additional kinetic energy must be added to raise vapor pressure of liquid phase of the solution to atmospheric pressure (1.00 atm) • The magnitude ofBP elevation is proportional to the number of particles the solute makes in solution

Change in Boiling Point Common Applications of Boiling Point Elevation

C. Freezing-Point Depression • Difference in temperature between the freezing point of solution and that of the pure solvent. • When a substance freezes, the particles of solid take on an orderly pattern the presence of a solute disrupts this pattern • Magnitude of freezing pointdepressionis proportional to number of particles the solutes makes in solution

Color code Graph

Change in Freezing Point Ethylene glycol/water solution Pure water The freezing point of a solution is LOWERthan that of the pure solvent. FP depression = ∆TFP = Kf•m

Change in Freezing Point Common Applications of Freezing Point Depression Ethylene glycol – deadly to small animals Propylene glycol

Change in Freezing Point • Which would you use for the streets of Dallas to lower the freezing point of ice and why? • Would the temperature make any difference in your decision? • sand, SiO2 • Rock salt, NaCl • Ice Melt, CaCl2 Common Applications of Freezing Point Depression

Boiling Point Elevation and Freezing Point Depression ∆T = K•m•i i = number of particles produced per formula unit. For covalent compounds, i = 1. For ionic compounds, i = the number of ions present (both + and -) Compound Theoretical Value of i Glycol C2 H6 O 2 1 NaCl 2 CaCl2 3

Boiling Point Elevation and Freezing Point Depression ∆T = K•m•i m = molality K = molal freezing point/boiling point constant

D. Osmosis, Osmotic Pressure (p) • Net movement of water in the direction opposite to the diffusion of solute • A semipermeable membraneallows the passage of solvent molecules but blocks the passage of solute molecules. • Important Biological function/ reverse osmosis ( fresh water) Osmotic pressure (p) is the pressure required to stop osmosis. more concentrated dilute

Physical Properties of Solutions Review and Colligative Properties