Mixtures and Solutions

• Solutions involve mixtures and molecular interactions affecting properties like solubility.
• Properties of solutions include osmosis, osmotic pressure, and dialysis.

Mixtures and Solutions

• Chemical reactions and biological processes commonly occur in water, making understanding solutions crucial.
• A solution is a homogenous mixture of two or more substances.
• The solute is the substance present in a smaller amount
• The solvent is the substance present in a larger amount.
• Solutions can exist as gases, solids, or liquids like seawater.
• Aqueous solutions involve a solvent that is water with either a liquid or solid solute.
• Solutes in water are either electrolytes or non-electrolytes.
• Electrolytes conduct electricity where as non-electrolytes do not when dissolved in water.
• Strong electrolytes are assumed to be 100% dissociated into ions (cations and anions) in solution.
• Hydration is the process where water molecules surround ions in a specific arrangement, stabilizing them and preventing recombination.

Solution Process

• Water is an effective solvent for ionic compounds.
• The process of dissolving involves the solute dispersing, requiring energy to pull apart molecular units which works against solution formation.
• Introducing the solute into the solvent can be either favorable or unfavorable, depending on the nature of the solute and solvent.
• A solutes solubility depends on the attractive forces between solute-solute and solvent-solvent molecules compared to solute-solvent pairs.
• Greater attraction between solute and solvent favors solution formation.
• More energy released in step 2 compared to step 1 favors solution formation and solute solubility.
• An increase in entropy can favor the dissolved state.
• Dissolving a solid in liquid is a two-step process
• The solid crystal-lattice breaks down in an endothermic process.
• Individual particles are surrounded by solvent molecules in an exothermic process
• The overall process is endothermic or exothermic depending on the net balance

Colligative Properties

• Colligative properties depend on the concentration of solute molecules or ions.
• These properties do not depend on the identity of the solute, and include:
• Vapor pressure lowering
• Boiling point elevation
• Freezing point depression
• Osmotic pressure

Examples of Colligative Properties

• Adding salt to water lowers the freezing temperature and raises the boiling temperature.
• Adding alcohol to water lowers the freezing point.

Lowering of Vapour Pressure

• In a pure solvent, the entire surface is occupied by solvent molecules.
• Adding a non-volatile solute results in both solute and solvent molecules on the surface, reducing the fraction of surface covered by solvent molecules.
• The vapour pressure of the solution is solely due to solvent so the solution has lower vapour pressure.
• Lowering in vapour pressure occurs between the vapour pressure of pure solvent and the vapour pressure of the solution.
• The ratio of this is known as the relative lowering of vapour pressure.
• Raoult established in 1886, a relation between the relative lowering in vapour pressure and mole fraction known as Raoult's law.
• Raoult's Law - the relative lowering in vapour pressure of a dilute solution is equal to the mole fraction of the solute present in the solution.
• Po - Ps / Po = n/n + N
• Po is the vapour pressure of pure solvent
• Ps is the vapour pressure of solution
• n is moles of solute
• N is moles of solvent

Elevation in Boiling Point

• The boiling point of a liquid is the temperature at which vapour pressure equals atmospheric pressure.
• Adding a non-volatile liquid to a pure solvent decreases the vapour pressure.
• The temperature of the solution must be increased to make vapour pressure equal to atmospheric pressure.
• Elevation in boiling point is the difference between the boiling point of the solution and the pure solvent.

Depression in Freezing Point

• The freezing point is defined as the temperature at which the vapour pressure of a substance's liquid is equal to the vapour pressure of the corresponding solid.
• Raoult's law states that adding a non-volatile solid to a solvent lowers its vapour pressure, causing it to equal that of solid solvent at a lower temperature.
• Depression in freezing point is the difference between the freezing point of the pure solvent and the solution.
• The elevation of boiling point is given by ΔT = Kbb, where Kb is the ebullioscopic constant.
• The depression of freezing point is given by ΔT = Kfb, where Kf is the cryoscopic constant.

Osmosis

• When a semipermeable membrane is placed between a solution and solvent, solvent molecules enter the solution.
• Flow of solvent molecules through a semipermeable membrane from pure solvent to a solution or between solutions with differing concentrations.
• The semi-permeable membrane allows only solvent molecules to pass through, not bigger solute molecules.
• Osmotic pressure stops the flow of solvent by applying extra pressure to the solution side.
• Osmotic pressure is a colligative property dependent on the number of solute but not its nature.
• Osmotic pressure (TT) is directly proportional to molarity (C) and temperature (T).
• Osmosis is the spontaneous passage of a pure solvent into a solution separated by a semipermeable membrane.
• Osmosis occurs through a membrane permeable to the solvent but not to the solute.
• The osmotic pressure is the pressure that must be applied to the solution to halt the influx of solvent.

Isotonic, Hypotonic, Hypertonic Solutions

• Isotonic solutions have the same osmotic pressure at a given temperature with no osmosis occuring through a semi-permeable membrane.
• A hypotonic solution has a lower osmotic pressure than the surrounding, where the solute concentration is less with respect to the surrounding.
• A hypotonic solution separated by semipermeable membrane causes water to move out the solution.
• A hypertonic solution has a higher osmotic pressure than the surrounding, where the solute concentration is more with respect to the surrounding
• A hypertonic solution separated by semipermeable membrane then water moves inside the solution.
• Common examples of isotonic solutions include 0.9% normal saline and lactated ringers.
• Isotonic solutions are useful for patients with fluid loss from blood loss, trauma, or dehydration from nausea/vomiting or diarrhea.
• Isotonic solutions have a concentration of dissolved particles similar to plasma.
• They have an osmolality of 250 to 375 mOsm/L. These fluids remain within the extracellular compartment and distribute between intravascular and interstitial spaces, increasing intravascular volume.
• Blood is examples of an isotonic solution.
• Tap water and pure water are hypotonic.

Gas Solubility

• The solubility of gases in liquids decreases with increasing temperature.
• Adding heat to a solution provides thermal energy, overcoming attractive forces between the gas and molecules, decreasing gas solubility.
• Four major factors affect the solubility of gases inside liquids:
• Pressure
• Temperature
• Size
• Chemical reactivity.
• Increasing pressure usually increases gas solubility inside a liquid, in accordance with Henry's law.

Impact on Biology

• With each breath, about 500 cm3 of air is inhaled.
• Airflow results from lung volume changes as the diaphragm depresses and the chest expands, reducing pressure by about 100 Pa
• The lungs have about 6 dm3 of air, with an additional 1.5 dm3 that can be exhaled after normal expiration.
• The lungs always retains some air preventing collapse of the alveoli.
• Gas exchange within alveoli causes changing air composition from cycle to cycle.
• Alveolar gas is a mix of both exhaled and newly inhaled air.
• Oxygen content of arterial blood corresponds to partial pressure of around 40 Torr (5.3 kPa).
• Partial pressure of freshly inhaled air is about 104 Torr (13.9 kPa).
• Capillary blood in the alveolar wall stays around 0.75 s and saturates in about 0.25 s due to the steep pressure gradient.
• Fluid collecting in the lungs (like in pneumonia) thickens the respiratory membrane, which then will:
  • Slow diffusion
  • Cause body tissues to suffer from oxygen

Hyperbaric Chamber

• The partial pressure gradient is lower in the tissue, about 5 Torr(0.7 kPa) in blood versus 40 Torr (5.3 kPa) in air at equilibrium.
• In alveolar fluid carbon dioxide is more soluble than oxygen.
• Under elevated partial pressure, oxygen therapy can treat shock diseases, carbon monoxide poisoning, gangrene, and tetanus.
• In Scuba Diving air supplied at higher pressure, as pressure increases approximately 1 atm every 10 metres.
• Because a high concentration of nitrogen becomes soluble in fatty tissues, narcosis results in a symptom of intoxication.
• Ascending too quickly could lead to the bends, where nitrogen forms fatal obstructions.
• Many cases of scuba drowning can result from gas bubbles and loss of consciousness.

Colloids

• A colloid is a mixture with particles ranging from 1-1000 nanometers able to stay evenly distributed referred to as colloidal dispersions.
• In colloids, a substance is evenly dispersed in another.
  • The substance being dispersed is in the dispersed phase.
  • The substance where it is dispersed is in the continuous phase.
• To be considered as a colloid, the substance's dimensions must range between 1-1000 nanometers.
  • Substances that are smaller is a solution.
  • Substances that are larger is a suspension.
• Classifying colloids depends on the phases of the dispersed substance.
  • Sol is a colloidal suspension with solid particles in liquid
  • Emulsion is between two liquids
  • Foam has many gas particles trapped within either liquid or solid
  • Aerosols contains particles of either liquid or solid dispersed within gas

Preparation of Colloids

• Lyophilic and lyophobic colloidal solutions are generally prepared by different methods.

Preparation of Lyophilic colloids

• Lyophilic colloids have a strong interaction with the particles and medium.
• Mixing the dispersed phase and dispersion is easily done as colloidal solutions.
• Gelatin, gum, starch, egg, and albumin are types of substances that can be readily mixed in water to give a colloidal solution.
• They become reversible allowing them to precipitate, and then convert straight into a colloidal state.

Preparation of Lyophobic colloids

• Mainly can be prepared by two methods: condensation or dispersion.
• During condensation, smaller particles become condensed of colloidal size.
• Accomplished by methods of oxidisation, reduction, hydrolysis, and double decomposition.
• During dispersion, larger particles are broken down.

Oxidation

• A colloidal solution of sulphur can be obtained by bubbling oxygen through hydrogen sulphide in water. 2H₂S + O₂ → 2H₂O + 2S

Reduction

• Prepared by treating acqueous metals of gold, silver, platinum with stannous chloride formaldehyde.

Hydrolysis

• Salt solutions undergo hydrolysis when boiling dilute solutions of their salts which can result in ferric or aluminum hydroxides.

Double Decomposition

• Arsenic sulphide is obtaining passing hydrogen sulphide through arsenious oxide water.

Miscellaneous Condensation Methods

• Excessive Cooling can be done with colloids of ice in organic solvents.
• Also with exchange of the solvent colloids of sulphur, and phosphorous can mix in alcohol mixing with water creating solutions.
• Sols made of mercury and sulphur are prepared with vapor in water.

Purification of Colloids

• Methods will include things like dialysis and ultrafiltration.
• Electrolytes are a regular impurity to note, while being low in concentration they destabilize colloids.
• Ultrafiltration works with filtering the colloids, separating the electrolyte from the rest.
• Sols are poured on filters and electrolytes or smaller sizes pass depending on their size as filtrate.
• The application is slower, however an additional of solution to the sides can expedite it.