Solutions. Composition solute solvent dilute concentrated

Solutions

Composition

solutesolventdilute

concentrated

Composition

Molarity (M)—

the number of moles ofsolute per liter ofsolutionmol/L

Composition

Mass percent—

the mass of solute permass of solution x 100unit-less

Composition

Mole fraction ()—

the moles of solute pertotal moles of solution(solute) or the moles ofsolvent per total molesof solution (solvent)

Composition

Molality (m)—

the moles of solute perkilogram of solvent

mol/kg

Composition

Normality (N)—

the equivalents of soluteper liter of solution

eq/L

Composition

Equivalent—

the mass of an acid orbase that can furnish orreact with 1 mole ofprotons

Composition

Equivalent—

the mass of an oxidizingor reducing agent thatcan accept or furnish 1mole of electrons

Composition Practice

Mylanta® Liquid contains200mg of aluminumhydroxide for every 5mLof solution.

Composition Practice

1. Assuming that thealuminum hydroxide isthe only ingredient,what is the molarity ofthe solution?

Composition Practice

2. Assuming that thedensity of the solutionis 1g/mL, what is themass percent of thesolution?

Composition Practice

3. Assuming that themass of water is4800mg, what are themole fractions of boththe solute and thesolvent?

Composition Practice

4. What is the molalityof the solution?

5.What is the normality of thesolution?

1. 0.513 mol/L2. 4% (mass)3. 0.00953 = solute

0.990 = solvent

4. 0.534 mol/kg5. 1.538 eq/L

Energy of Solution Formation“like dissolves like”

due to the energy associated with the formation of a solutionStep 1: solute expands (endo)Step 2: solvent expands (endo)Step 3: solute and solvent

interact (usually exo)

Energy of Solution Formation

sum of steps 1-3 gives theenthalpy of solution, or heatof solution (Hsoln)

Hsoln= H1 + H2 + H3

Energy of Solution Formation

Consider mixing oil and water…They are immiscible.Oil molecules are large andhave LDF…thus, H1 will belarge and positive for theoil expansion

Energy of Solution Formation

Water molecules haveH-bonds…thus, H2 will belarge and positive for thewater expansion

Energy of Solution Formation

H3 will be small sincenonpolar and polar moleculestend to have no attractiveforces

Energy of Solution FormationHsoln will be large and positivebecause of the large impactthat H1 and H2 have.

Thus, it would require a largeamount of energy for the oiland water to mix

Energy of Solution Formation

Consider mixing NaCl andwater… They are soluble.NaCl formula units havestrong ionic forces…thus,H1 will be large and positivefor the NaCl expansion

Energy of Solution Formation

Again, water molecules haveH-bonds…thus, H2 will belarge and positive for thewater expansion

Energy of Solution Formation

H3 will be large andnegative since the attractiveforces between the ions andthe polar water moleculesare so strong

Energy of Solution Formation

The Hsoln for NaCl in water is actually 3 kJ/mol. It ispositive and small…and it ismore disordered than theoriginal NaCl and water…hence, favorable.

Solubility

•the amount of solute that dissolves in solvent

Factors Affecting Solubility

•Structure•Pressure•Temperature

Structure’s Effect

•A, D, E, & K are fat-soluble because nonpolar, long H-C chains (hydrophobic)

•B & C are water-soluble because they have polar

0-H and C-O bonds (hydrophilic)

Pressure’s Effect

•Gas in a liquid•Increased pressure above a liquid means increased solubility of a gas in the liquid…Henry’s Law

Henry’s Law

•Amount of a gas dissolved in solution is directly proportional to the pressure of the gas above the solution.

Henry’s Law•P = kC

•S1 = S2

P1 P2

•Obeyed particularly well in non-dissociated solutions

Temperature’s Effect•Most solids’ solubilities will increase as temperature is increased…but not all

•Must be determined by experimentation

Temperature’s Effect

Na2SO4

Na2SO

4

Temperature’s Effect•Gases’ solubilities will decrease as temperature is increased

•Thermal pollution

Lake Nyos, Cameroon

Lake Nyos, Cameroon

•August 21, 1986•>1700 people and >3000 cattle killed

•Lake turn-over thought to have been caused by volcanic activity

Lake Nyos, Cameroon

Vapor Pressure

•decreases with the addition of a nonvolatile solute to a solvent

•François Raoult studied the effects of a solute on vapor pressure

Raoult’s Law

•Psoln = (Posolvent)

(solvent)

•Linear relationship• y = mx + b

•b is zero

Raoult’s Law

•Psoln is the vapor pressure of the solution

•Posolvent is the vapor

pressure of the pure solvent

solvent is the mole fraction of the solvent

Raoult’s Law

•For volatile solutions,

•Ptotal = (PoA)(A) + (Po

B)(B)

Raoult’s Law•is to solutions what the ideal gas law is to gases

•Strong solute-solvent attraction results in a vapor pressure lower than what Raoult’s Law predicts

6. A carbonated beverage is bottled at 25°C with 5.00atm over the CO2 in the liquid. Assuming that the partial pressure of the CO2 in the atmosphere is

0.0004atm, calculate theequilibrium concentrations of CO2 before and after the bottle is opened. TheHenry’s Law constant forCO2 is 32Latm/mol at25°C

7. A solution was prepared by adding 20.0g of urea to 125g water at 25°C, the temperature at which water’s vapor pressure is 23.76torr. The

observed vapor pressureof the solution was

foundto be 22.67torr. What is the molar mass of urea?

8. A solution is prepared by mixing 5.81g acetone (C3H6O) and 11.9g chloroform (CHCl3). At 35°C this solution has a total vapor pressure of 260torr.

Is this an ideal solution?The vapor pressures ofpure acetone andchloroform at 35°C are345 and 293torr,respectively.

6.The unopened bottle’s CO2 concentration is 0.160 mol/L. The opened bottle’s concentration is 1.2 x 10-5 mol/L. That’s why it tastes flat.

7. The molar mass of urea is 59.7 g/mol.

8. The expected Ptotal is 319torr. Since Ptotal is actually 260torr, the solution does not behave ideally.

Colligative Properties•are dependent upon the number of solute particles dissolved in solution–Boiling point–Freezing point–Osmotic pressure

Boiling Point•is the temperature at which a substance’s vapor pressure equals the atmospheric pressure

•What effect does the addition of a nonvolatile solute have on vapor pressure?

Boiling Point•Thus, the boiling point of a solvent is elevated when a nonvolatile solute is added.

•The amount by which it increases is calculated by…

Tb = kbmsolutei

Boiling PointTb is the change in boiling point of the solution

•kb is the boiling point constant for the solvent

•msolute is the molality of the solute

•i is the van’t Hoff factor

Boiling Point

•van’t Hoff factor–the number of particles of dissolved solute per mole of solute…in other words, the number of dissociated particles

Boiling Point

•Know the boiling and point constant for water…

kb = 0.512°Ckg/mol

Freezing Point•is the temperature at which a solid’s vapor pressure equals its liquid’s vapor pressure

•A nonvolatile solute will lower the vapor pressure of the liquid.

Freezing Point•As the solution is cooled the vapor pressure of the pure solid decreases more rapidly than the vapor pressure of the pure liquid.

•Thus, the freezing point will be lowered.

Freezing Point

Tf = kfmsolutei

•Know the freezing point constant for water…

kf = 1.86°Ckg/mol

Osmotic Pressure•is the pressure needed to stop osmosis from occurring

•may be calculated using

= MRTi

Osmotic Presure is the osmotic pressure•M is the molarity of the solution

•R is the gas law constant, 0.08206 Latm/Kmol

•T is the Kelvin temperature

Osmotic Presure•When pressure greater than is applied, reverse osmosis will occur–Solute particles are filtered out

–Desalination is an example

•Isotonic solutions–same osmotic pressure

•Hypertonic solutions–migration of solvent out of cells results in crenation

•Hypotonic solutions–migration of solvent into cells results in hemolysis

9. My car’s cooling system contains 2.51kg of water and 2.45kg of ethylene glycol (antifreeze), C2H6O2. Below what temperature will my engine block freeze?

10. If I were to substitute the ethylene glycol with sodium chloride, below what temperature will my engine block freeze?

11. When 10.0g of camphor are added to 100g of benzene, To

b is 80.1°C and kb is 2.53 °Ckg/mol, the boiling point of the solution is 81.76°C. What is the molar mass of the camphor?

12. A 20.0-mg sample of a protein is dissolved in water to make 25.0mL of solution. The osmotic pressure of the solution is 0.56torr at 25°C. What is the molar mass of the protein?

9. -29.2 °C10. -62.1 °C11. 152g/mol12. 26550g/mol