Solutions.

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Presentation transcript:

Solutions

Composition solute solvent dilute concentrated

Composition Molarity (M)— the number of moles of solute per liter of solution mol/L

Composition Mass percent— the mass of solute per mass of solution x 100 unit-less

Composition Mole fraction ()— the moles of solute per total moles of solution (solute) or the moles of solvent per total moles of solution (solvent)

Composition Molality (m)— the moles of solute per kilogram of solvent mol/kg

Composition Normality (N)— the equivalents of solute per liter of solution eq/L

Composition Equivalent— the mass of an acid or base that can furnish or react with 1 mole of protons

Composition Equivalent— the mass of an oxidizing or reducing agent that can accept or furnish 1 mole of electrons

Composition Practice Mylanta® Liquid contains 200mg of aluminum hydroxide for every 5mL of solution.

Composition Practice Assuming that the aluminum hydroxide is the only ingredient, what is the molarity of the solution?

Composition Practice 2. Assuming that the density of the solution is 1g/mL, what is the mass percent of the solution?

Composition Practice 3. Assuming that the mass of water is 4800mg, what are the mole fractions of both the solute and the solvent?

Composition Practice 4. What is the molality of the solution? What is the normality of the solution?

0.513 mol/L 4% (mass) 0.00953 = solute 0.990 = solvent 0.534 mol/kg 1.538 eq/L

Energy of Solution Formation “like dissolves like” due to the energy associated with the formation of a solution Step 1: solute expands (endo) Step 2: solvent expands (endo) Step 3: solute and solvent interact (usually exo)

Hsoln= H1 + H2 + H3 sum of steps 1-3 gives the Energy of Solution Formation sum of steps 1-3 gives the enthalpy of solution, or heat of solution (Hsoln) Hsoln= H1 + H2 + H3

Energy of Solution Formation Consider mixing oil and water… They are immiscible. Oil molecules are large and have LDF…thus, H1 will be large and positive for the oil expansion

Energy of Solution Formation Water molecules have H-bonds…thus, H2 will be large and positive for the water expansion

Energy of Solution Formation H3 will be small since nonpolar and polar molecules tend to have no attractive forces

Energy of Solution Formation Hsoln will be large and positive because of the large impact that H1 and H2 have. Thus, it would require a large amount of energy for the oil and water to mix

Energy of Solution Formation Consider mixing NaCl and water… They are soluble. NaCl formula units have strong ionic forces…thus, H1 will be large and positive for the NaCl expansion

Energy of Solution Formation Again, water molecules have H-bonds…thus, H2 will be large and positive for the water expansion

Energy of Solution Formation H3 will be large and negative since the attractive forces between the ions and the polar water molecules are so strong

Energy of Solution Formation The Hsoln for NaCl in water is actually 3 kJ/mol. It is positive and small…and it is more disordered than the original 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 Na2SO4

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

Psoln = (Posolvent)(solvent) Linear relationship y = mx + b Raoult’s Law Psoln = (Posolvent)(solvent) Linear relationship y = mx + b b is zero

solvent is the mole fraction of the solvent 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

For volatile solutions, Ptotal = (PoA)(A) + (PoB)(B) Raoult’s Law For volatile solutions, Ptotal = (PoA)(A) + (PoB)(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 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 the equilibrium concentrations of CO2 before and after the bottle is opened. The Henry’s Law constant for CO2 is 32Latm/mol at 25°C

7. A solution was prepared by adding 20 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 pressure of the solution was found to be 22.67torr. What is the molar mass of urea?

8. A solution is prepared by mixing 5. 81g acetone (C3H6O) and 11 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 of pure acetone and chloroform at 35°C are 345 and 293torr, respectively.

The unopened bottle’s CO2 concentration is 0. 160 mol/L 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?

Tb = kbmsolutei 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 Point Tb 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

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

Know the boiling and point constant for water… 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.

Know the freezing point constant for water… Tf = kfmsolutei Know the freezing point constant for water… kf = 1.86°Ckg/mol

 = MRTi Osmotic Pressure is the pressure needed to stop osmosis from occurring may be calculated using  = MRTi

 is the osmotic pressure M is the molarity of the solution 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

When pressure greater than  is applied, reverse osmosis will occur Osmotic Presure When pressure greater than  is applied, reverse osmosis will occur Solute particles are filtered out Desalination is an example

Isotonic solutions Hypertonic solutions Hypotonic 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 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, Tob is 80 11. When 10.0g of camphor are added to 100g of benzene, Tob 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 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?

-29.2 °C -62.1 °C 152g/mol 26550g/mol