Solutions. A homogeneous mixture in which all of the particles have the sizes of atoms. Driving forces for solution formation Spontaneous tendency for increasing disorder (entropy!) Intermolecular forces. Sugar or alcohol in water.
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A homogeneous mixture in which all of the particles have the sizes of atoms.
Sugar or alcohol in water
Water and ethyl alcohol are completely "miscible". Both water and ethanol are polar molecules with hydrogen bonding. The similarity of the two molecules results in solutions where the water and alcohol molecules are interchangeable. Note that hexanol is only partially soluble in water (miscible with hexane though!).
Glucose dissolves in water because polar water molecules attach to the glucose molecules by dipole-dipole (H-bond) forces. When the attractive forces of the water molecules for the glucose exceeds the attractive forces between the glucose and its neighbouring glucose molecules the water can rip the sugar molecule out of the crystal. The glucose is "solvated" when it surrounded solvent molecules. The solvent has "dissolved" the molecule.
dry cleaning, surfactants and oxidizing agents
Heat of solution: The enthalpy change between system and surroundings when 1 mole of a solute dissolves in solvent at constant pressure
Physical properties that depend only upon the populations of particles in a mixture
Effect of solutes on the vapour pressure of solutions
Psoln = xsolventP*solvent Raoult’s Law
Molecular interpretation of Raoult’s Law
Each component contributes its own partial pressure to the solution vapour pressure (Dalton’s Law)
Deviations because of intermolecular attractions
Entropy effect (see later): when a solute is added to a pure liquid, the entropy (disorder) is increased relative to the vapour phase. Therefore there is a weaker tendency to form a vapour (boiling point elevation). A similar molecular interpretation explains freezing point depression. The effect shifts the s-l and l-g vp curve of a phase diagram down.
Osmotic membrane: semi-permeable membrane that allows passage of only solvent molecules
Dialysis membrane: membrane that allows passage of solvent and small solutes.
Van’t Hoff equation
1.00 m NaCl: F.P= -3.37C (not –1.86C as expected)!
Colligative properties depend on the concentration of particles
Remember: NaCl Na+ + Cl-
We have 2.00m of particles and should get F.P: -(2x1.86C) = -3.72C
Effect of interionic attractions account for discrepancy between actual and calculated F.P. for ionic species.
Van’t Hoff Factor compares degrees of dissociation of electrolytes