. Chapter 12 - Solutions Chapter 12 - Solutions Solutions, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Pure substances . We’ve seen that the physical properties of a pure substance are dependent on the strength of the intermolecular forces between the molecules Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Solutions . Solutions are “mixtures” of two or more pure substances. The substance found in greater amounts is usually referred to as the SOLVENT, while all other substances in the solution are considered to be the SOLUTE(S). Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Solutions . Solutes and solvents only tend to mix (are MISCIBLE) when the intermolecular forces of the solvent and solute(s) are of similar strengths. “Like dissolves like” Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Figure If molecules A and B have large differences in intermolecular force strengths, then a molecule of A will be “sucked back” into pure A instead of mixing with pure B. Oil (London forces) and water (hydrogen bonds) DON’T MIX, and are said to be IMMISCIBLE. . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Figure If molecules A and B have similar intermolecular force strengths, then a molecule of A can mix with pure B. Alcohols (hydrogen bonds) and water (hydrogen bonds) DO MIX! . Solutions and Osmosis, Paul G. Mezey

Physical properties of solutions Chapter 12 - Solutions Physical properties of solutions Even though “like dissolves like”, the presence of solute molecules in the solvent disrupts the bulk solvent intermolecular forces to some extent. This change in forces means that the physical properties of solutions, like freezing and boiling points, are slightly different than those of the pure solvent. . Solutions and Osmosis, Paul G. Mezey

Physical properties of solutions Chapter 12 - Solutions Physical properties of solutions The disruption of forces generally depends more on the amount of solute (in terms of concentration) rather than the chemical identity of the solute. Such colligative properties of solutions therefore depend on the concentration of the solution while ignoring the identity of the solute. . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Dilution of solutions If we take a solution and add pure solvent to it, we expect dilution to occur. The solution and solvent mix until a new solution of lower concentration is made. . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Dilution of solutions If we instead take a solution and separate it from pure solvent using a semipermeable membrane that solute molecules can’t pass through, then we are “controlling the mixing.” . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Osmosis . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Osmosis . Osmosis is the process where the solvent passes through the semipermeable membrane driven by the trend to EQUALIZE the solute concentration on both sides of the membrane. Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Osmosis . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Osmotic pressure . Osmotic pressure is a colligative property of a solution that is defined as the external pressure that must be applied to a solution to just stop the process of osmosis through the membrane. Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Osmotic pressure . Osmotic pressure P depends on the concentration of the solution (M), the temperature (T) and the gas constant (R). P = MRT Solutions and Osmosis, Paul G. Mezey

Osmotic pressure and molar mass Chapter 12 - Solutions Osmotic pressure and molar mass 1. Make a solution of a certain mass of solute in a given total volume. 2. Measure the osmotic pressure. 3. Calculate M from measured P and T. Use M and volume to calculate the moles of solute. 5. Use moles and mass of solute to calculate molar mass. . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Problem . An aqueous solution of 21.6 mg of vasopressin in 100.0 mL of solution has an osmotic pressure at 25 C of 3.70 mmHg. What is the molar mass of the hormone? Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions Osmosis and biology Cell walls are often semipermeable membranes that allow water to pass through, but not many solute molecules. Body fluids, like blood plasma, must have concentrations that match those inside the cell or osmosis might cause cells to shrink or rupture. . Solutions and Osmosis, Paul G. Mezey

Blood cells and osmosis Chapter 12 - Solutions Blood cells and osmosis Normal blood cell in isotonic (same concentration) solution. No osmosis. Collapsed blood cell in hypertonic (more concentrated) solution. Water leaves the cell during osmosis. Bloated blood cell in hypotonic (less concentrated) solution. Water enters the cell during osmosis. . Solutions and Osmosis, Paul G. Mezey

Solutions and Osmosis, Paul G. Mezey Chapter 12 - Solutions . Solutions and Osmosis, Paul G. Mezey

Be Careful Be Careful ! . Attention, Paul G. Mezey