Chapter 5: Physical Properties of Solutions PDF

# Chapter 5: Physical Properties of Solutions ## Introduction - A **solution** is a homogeneous mixture of two or more substances. - **Solute(s)** are the substance(s) present in the smaller amount (the substance that is being dissolved). - **Solvent** is the substance present in the larger amount...

# Chapter 5: Physical Properties of Solutions ## Introduction - A **solution** is a homogeneous mixture of two or more substances. - **Solute(s)** are the substance(s) present in the smaller amount (the substance that is being dissolved). - **Solvent** is the substance present in the larger amount (the substance that dissolves the solute). ## Types of Solutions The table summarizes the types of solutions based on the state of the solute and solvent: | Component 1 | Component 2 | State of Resulting Solution | Examples | |---|---|---|---| | Gas | Gas | Gas | Air | | Gas | Liquid | Liquid | Soda water (CO₂ in water) | | Gas | Solid | Solid | H₂ gas in palladium | | Liquid | Liquid | Liquid | Ethanol in water | | Solid | Liquid | Liquid | NaCl in water | | Solid | Solid | Solid | Brass (Cu/Zn), solder (Sn/Pb) | ## Types of Solutions Based on Solute Concentration - **Saturated solution** contains the maximum amount of solute a solvent can dissolve at a specific temperature. - **Unsaturated solution** contains less solute than the solvent can dissolve at a specific temperature. - **Supersaturated solution** contains more solute than is present in a saturated solution at a specific temperature. Sodium acetate crystals rapidly form when a "seed crystal" is added to a supersaturated solution of sodium acetate. ## Interactions in the Solution Process There are three types of interactions involved in the solution process: - **Solvent-solvent interaction** - **Solute-solute interaction** - **Solvent-solute interaction** ## Like Dissolves Like - Non-polar molecules are soluble in non-polar solvents (e.g. CCl₄ in C₆H₆). - Polar molecules are soluble in polar solvents (e.g. Ethanol C₂H₅OH in H₂O). - Ionic compounds are more soluble in polar solvents (e.g. NaCl in H₂O or NH₃). ## Concentration Units The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. ### Percent by Mass % by mass = mass of solute / (mass of solute + mass of solvent) x 100% = mass of solute / mass of solution x 100% ### Mole Fraction (X) X_A = moles of A / sum of moles of all components ### Molarity (M) M = moles of solute / liters of solution ### Molality (m) m = moles of solute / mass of solvent (kg) ## Dilution - Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. - Moles of solute before dilution (i) = moles of solute after dilution (f). - M_iV_i = M_fV_f ## Osmotic Pressure (π) - **Osmosis** is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. - A **semipermeable membrane** allows the passage of solvent molecules but blocks the passage of solute molecules. - **Osmotic pressure (π)** is the pressure required to stop osmosis. - π = MRT - M is the **molarity** of the solution - R is the **gas constant** - T is the **temperature** (in K) ## Colloids - A **colloid** is a dispersion of particles of one substance throughout a dispersing medium of another substance. ### Colloid versus Solution - Colloidal particles are much larger than solute molecules. - Colloidal suspension is not as homogeneous as a solution. - Colloids exhibit the **Tyndall effect** (the scattering of light as it passes through a colloid). ### Types of Colloids The table summarises the type of colloid based on medium and dispersed phase: | Dispersing Medium | Dispersed Phase | Name | Example | |---|---|---|---| | Gas | Liquid | Aerosol | Fog, mist | | Gas | Solid | Aerosol | Smoke | | Liquid | Gas | Foam | Whipped cream | | Liquid | Liquid | Emulsion | Mayonnaise | | Liquid | Solid | Sol | Milk of magnesia | | Solid | Gas | Foam | Plastic foams | | Solid | Liquid | Gel | Jelly, butter | | Solid | Solid | Solid sol | Certain alloys (steel), opal | ### Hydrophilic and Hydrophobic Colloids - **Hydrophilic colloids** are water-loving. - **Hydrophobic colloids** water-fearing. ### Stabilization of a Hydrophobic Colloid Hydrophobic colloids can be stabilized by the use of surfactants. Surfactants have both hydrophilic and hydrophobic ends. The hydrophobic ends adsorb to the surface of the hydrophobic colloid, while the hydrophilic ends extend into the surrounding water, providing a layer of hydration and preventing the colloid particles from aggregating. ## The Cleansing Action of Soap Soap is a surfactant, with a hydrophilic "head" and a hydrophobic "tail". - The **hydrophobic tail** (long hydrocarbon chain) dissolves the grease (non-polar) and gets attracted to it. - The **hydrophilic head** (polar carboxylate group) is attracted to the water. - This forms a **micelle**, with the grease molecules trapped inside and the hydrophilic heads on the outside, allowing the grease to be easily washed away by water. ## Chemistry In Action: Desalination Desalination is the process of removing salt from seawater to produce drinkable freshwater. This can be achieved using various methods, including: - **Solar radiation:** Sunlight is used to evaporate seawater, leaving the salt behind. The vapor is then collected to obtain fresh water. ## Chemistry In Action: Reverse Osmosis - Reverse osmosis is a method of desalination where pressure is applied on the membrane to remove salt from saltwater. - Seawater is forced through a semi-permeable membrane, which allows water molecules to pass but blocks larger salt ions. The document describes the physical properties of solutions including: - Types of solutions based on the state of the solute and solvent. - Types of solutions based on the solute concentration. - Interactions involved in the solution process. - Different units to measure the concentration. - The process of dilution. - Osmotic pressure. - And the properties of colloids, including the Tyndall effect, the difference between hydrophilic and hydrophobic colloids and the cleansing action of soap. - It also includes examples of practical applications of solutions, like desalination using reverse osmosis.