Solutions and Solubility
- “Like dissolves Like” (don’t say it in exam) → Water dissolves polar molecules (have dipole moment) and does not dissolve nonpolar molecules
- polar–polar and nonpolar–nonpolar → are more attracted to each other than themselves → the heat of solution is expected to be small → solution forms because the process is energetically favorable
- Nonpolar-Nonpolar: the larger and more polarizable the electron cloud = stronger LDF = the more interactions will occur with the solvent → increases solubility
- Solutions form when the solute and solvent attract to each other more than themselves
- Polar–nonpolar and nonpolar–polar → are more attracted to themselves than each other → heat of solution is expected to be large and positive → large amount of energy required prevents solution formation
Solution Particle Diagrams
- In questions, will have to show charges on ions, multiple water molecules oriented correctly, correct sizes (anion bigger than cation) and number of particles
Factors Affecting Solubility
Structure Effects
- Substances with similar intermolecular forces tend to be soluble (solid solute) in one another
- Molecular structure determines polarity → structure and solubility are connected
- Hydrocarbons: Long chains of covalently bonded carbon and hydrogen
- Nonpolar (Hydrophobic)
- Only polar if has electronegative charge (O2, Su, F, N → electronegative atoms)
- Nonpolar (Hydrophobic)
Pressure Effects
- Pressure does not affect the solubilities of solids or liquids but does increase the solubility of a gas
- Pressure increases → compresses gas molecules, creating room for additional gas molecules and forcing more of them into the solution
Temperature Effects (For Aqueous Solutions)
- Most solids are more soluble at higher temps (there are some important exceptions), but the amount of solid that can be dissolved may increase or decrease with increasing temperature
- Solubility of gasses in liquids decreases with increasing temperature
- Increasing temp → increases KE of gas particles → causes more motion and they break interMF more easily → solute and solvent can’t interact to form a solution as efficiently
Intermolecular Forces
- Stronger InterMF → increases attraction between the solute molecules and solvent → increases solubility