1. Chapter Nine
Solutions

2. Outline 9.1 Mixtures and Solutions 9.2 The Solution Process
9.3 Solid Hydrates
9.4 Solubility
9.5 The Effect of Temperature on Solubility
9.6 The Effect of Pressure on Solubility: Henry’s Law
9.7 Units of Concentration
9.8 Dilution
9.9 Ions in Solution: Electrolytes
9.10 Electrolytes in Body Fluids: Equivalents and Milliequivalents (omit)
9.11 Properties of Solutions
9.12 Osmosis and Osmotic Pressure
9.13 Dialysis
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3. Goals
1. What are solutions, and what factors affect solubility? Be able to define the different kinds of mixtures and explain the influence on solubility of solvent and solute structure, temperature, and pressure.
2. How is the concentration of a solution expressed? Be able to define, use, and convert between the most common ways of expressing solution concentrations.
3. How are dilutions carried out? Be able to calculate the concentration of a solution prepared by dilution and explain how to make a desired dilution.
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4. Goals Contd.
4. What is an electrolyte? Be able to recognize strong and weak electrolytes and nonelectrolytes, and express electrolyte concentrations.
5. How do solutions differ from pure solvents in their behavior? Be able to explain vapor pressure lowering, boiling point elevation, and freezing point depression for solutions.
6. What is osmosis? Be able to describe osmosis and some of its applications.
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5. 9.1 Mixtures and Solutions
Heterogeneous mixture: A nonuniform mixture that has regions of different composition.
Homogeneous mixture: A uniform mixture that has the same composition throughout.
Solution A homogeneous mixture that contains particles the size of a typical ion or small molecule.
Colloid A homogeneous mixture that contains particles in the range 2–500 nm diameter.
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6. Liquid solutions, colloids, and heterogeneous mixtures can be distinguished in several ways.
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7. 9.2 The Solution Process
A good rule of thumb for predicting solubility is that “like dissolves like”. Substances with similar intermolecular forces form solutions and substances with different intermolecular forces do not.
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8. Dissolution of an NaCl crystal in water
Dissolution of an NaCl crystal in water. Polar water molecules surround individual ions pulling them from the crystal surface into solution. Oxygen atoms point to (+) ions and hydrogen atoms point to (-) ions.
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9. 9.3 Solid Hydrates
Some ionic compounds attract water strongly enough to hold onto water molecules even when crystalline, forming what are called solid hydrates.
Plaster of Paris, CaSO4·1/2H2O, is a solid hydrate. The formula indicates that for every 2 formula units of calcium sulfate in the crystal there is also one water.
Still other ionic compounds attract water so strongly that they pull water vapor from humid air to become hydrated. Compounds that show this behavior, such as calcium chloride are called hygroscopic and are often used as drying agents.
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11. 9.4 Solubility
Hydrogen bonding between water and ethanol, between water alone, and ethanol alone is so similar that the two liquids are miscible, or mutually soluble in all proportions.
Most substances reach the limit of a saturated solution: A solution that contains the maximum amount of dissolved solute at equilibrium.
Solubility: The maximum amount of a substance that will dissolve in a given amount of solvent at a specified temperature.
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12. 9.5 The Effect of Temperature on Solubility
Temperature often has a dramatic effect on solubility.
The effect of temperature is different for every substance, however, and is usually unpredictable.
Solids that are more soluble at high temperature than at low temperature can sometimes form what are called supersaturated solutions, which contain even more solute than a saturated solution.
Such a solution is unstable and precipitation can occur dramatically when a tiny seed crystal is added.
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13. Most solid substances become more soluble as temperature rises.
Solubility of some (a) solids and (b) gases, in water as a function of temperature.
Most solid substances become more soluble as temperature rises.
The solubility of gases decreases as temperature rises.
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14. 9.6 The Effect of Pressure on Solubility: Henry’s Law
Henry’s law: The solubility of a gas is directly proportional to its partial pressure. If T is constant, C  Pgas , or C/Pgas = k , or C1/P1 = C2/P2 .
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15. 9.7 Units of Concentration
Solute: A substance dissolved in a liquid.
Solvent: The liquid in which a substance is dissolved.
Solution: The combination of solute and solvent.
A very useful means of expressing concentration in the laboratory is molarity (M), the number of moles of solute dissolved per liter of solution.
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16. Weight/Volume Percent Concentration [(w/v)%]
Mathematically, (w/v)% concentration is found by taking the number of grams of solute per milliliters of solution and multiplying by 100.
Volume/Volume Percent Concentration [(v/v)%]
Mathematically (v/v)% is determined from the volume of solute (usually in mL) per milliliter of solution multiplied by 100.
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17. Parts per Million (ppm) and Parts per Billion (ppb): When concentrations are very small, as often occurs in dealing with trace amount of pollutants or contaminants, parts per million (ppm) or parts per billion (ppb) units are used.
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18. To prepare 100 mL of a specific solution, the solute is measured out and dissolved in just enough solvent to give a final volume of 100 mL.
If the solute were dissolved in 100 mL of solvent, the final volume of the solution will likely be a bit larger or smaller than 100 mL.
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19. 9.8 Dilution
Dilution: Lowering concentration by adding additional solvent.
Dilution factor: The ratio of the initial and final solution volumes (V1/V2).
In the dilution process, the amount of solute remains constant, only the volume is increased.
Moles of solute = M1V1 = M2V2 = constant
Dilution equations can be generalized to other concentration units, C1V1 = C2V2
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20. The following equation is very useful in calculating final concentration of a solution after dilution.
M2 V1 =M2V2
M1 and V1 refers to the initial concentration and volume of the solution and M2 and V2 refers to the final concentration and volume of the solution.
The final concentration will be equal to the product of the initial concentration and the dilution factor.
M2 = M1 · (V1/V2).
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21. 9.9 Ions in Solution: Electrolytes
Electrolyte: A substance that produces ions and therefore conducts electricity when dissolved in water.
Strong electrolyte: A substance that ionizes completely when dissolved in water.
Weak electrolyte: A substance that is only partly ionized in water.
Nonelectrolyte: A substance that does not produce ions when dissolved in water.
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22. 9.11 Properties of Solutions
The properties of solutions are similar in many respects to those of pure solvents, but there are some important differences.
The properties of a solution that depend on the concentration of a dissolved solute but not on its identity are known as colligative properties.
Vapor pressures are lower, boiling points are higher and freezing points are lower in solutions than they are in a pure solvent.
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23. For each mole of solute particles added the boiling point of 1 kg of water is raised by 0.51°C. 1 mol of a molecular substance like glucose raises the boiling point of 1 kg of water from 100.0°C to °C. The addition of 1 mol of NaCl per kilogram of water raises the boiling point by 2 * 0.51°C = 1.02°C because the solution contains 2 mol of solute particles.
For each mole of solute particles, the freezing point of 1 kg of water is lowered by 1.86°C. 1 mol of antifreeze per kilogram of water lowers the freezing point from 0.00°C to °C and 1 mol of NaCl (2 mol of particles) per kilogram lowers the freezing point from 0.00° C to -3.72°C.
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24. A close-up plot of vapor pressure versus temperature
for pure water (red curve) and for a 1.0 M NaCl solution (green curve). Pure water boils at 100.0°C, but the solution does not boil until 101.0°C.
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25. 9.12 Osmosis and Osmotic Pressure
Osmosis: The passage of solvent through a semipermeable membrane separating two solutions of different concentration.
Osmotic pressure: The amount of external pressure applied to the more concentrated solution to halt the passage of solvent molecules across a semipermeable membrane.
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27. Isotonic: Having the same osmolarity.
Osmolarity (osmol): The sum of the molarities of all dissolved particles in a solution.
Isotonic: Having the same osmolarity.
Hypotonic: Having an osmolarity less than the surrounding blood plasma or cells.
Hypertonic Having an osmolarity greater than the surrounding blood plasma or cells.
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28. In (a) an isotonic solution, 0
In (a) an isotonic solution, 0.30 osmol, the blood cells are normal in appearance.
The cells in (b) a hypotonic solution are swollen because of water gain, and may burst, a process called hemolysis.
Those in (c) a hypertonic solution are shriveled because of water loss, this process is called crenation.
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29. 9.13 Dialysis
Dialysis is similar to osmosis, except that the pores in a dialysis membrane are larger than those in an osmotic membrane so that both solvent molecules and small solute particles can pass through, but large colloidal particles such as proteins cannot pass.
Hemodialysis is used to cleanse the blood of patients whose kidneys malfunction. Blood is diverted from the body and pumped through a long cellophane dialysis tube suspended in an isotonic solution formulated to contain many of the same components as blood plasma.
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30. Small waste materials such as urea pass through the dialysis membrane from the blood to the solution side where they are washed away.
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31. Chapter Summary
Mixtures are classified as either heterogeneous or homogeneous. Solutions are homogeneous mixtures that contain particles the size of ions and molecules whereas larger particles (2.0–500 nm diameter) are present in colloids.
The maximum amount of a solute that can be dissolved in a solvent is called the solubility. Substances tend to be mutually soluble when their intermolecular forces are similar.
The solubility in water of a solid often increases with temperature, but the solubility of a gas decreases with temperature.
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32. Chapter Summary Contd.
Pressure significantly affects gas solubility, which is directly proportional to the partial pressure over the solution (Henry’s law).
The concentration of a solution can be expressed in several ways, including molarity, weight/weight percent composition, weight/volume percent composition, and parts per million.
Molarity, the number of moles of solute per liter of solution, is the most useful method when calculating quantities of reactants or products for reactions in aqueous solution.
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33. Chapter Summary Contd.
A dilution is carried out by adding more solvent to an existing solution. Only the amount of solvent changes; the amount of solute remains the same.
Substances that form ions when dissolved in water and whose water solutions therefore conduct an electric current are called electrolytes.
Strong electrolytes ionize completely in water, weak electrolytes ionize partially, and nonelectrolytes do not ionize in water.
Fluids containing many different electrolytes have concentrations expressed in equivalents.
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34. Chapter Summary Contd.
A solution has a lower vapor pressure, a higher boiling point, and a lower melting point than a pure solvent.
Colligative properties depend only on the number of dissolved particles, not on their chemical identity.
Osmosis occurs when solutions of different concentration are separated by a semipermeable membrane that allows solvent molecules to pass but blocks the passage of solute ions and molecules.
In dialysis, the membrane allows the passage of solvent and small dissolved molecules but prevents passage of proteins and larger particles.
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35. Key Words Colligative property Colloid Dilution factor Electrolyte
Equivalent (Eq)
Gram-equivalent
Henry’s law
Heterogeneous mixture
Homogeneous mixture
Hygroscopic
Hypertonic
Hypotonic
Isotonic
Miscible
Molarity (M)
Nonelectrolyte
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36. Key Words Contd. Osmolarity (osmol) Osmosis Osmotic pressure
Parts per billion (ppb)
Parts per million (ppm)
Saturated solution
Solubility
Solute
Solution
Solvation
Solvent
Strong electrolyte
Supersaturated solution
Volume/volume percent concentration, (v/v)%
Weak electrolyte
Weight/volume percent concentration, (w/v)%
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