Chemistry

• Solution is a homogeneous mixture of two or more pure substances, with the solute being the substance in small quantity dissolved in the solvent, forming the solution
• Solubility is the amount of solute dissolved in 100 g of solvent at a given temperature to form a saturated solution
• Factors affecting solubility:

  • Inter-ionic attraction in solute molecules
  • Inter-molecular attraction between solvent and solute molecules
  • Solvation: force of attraction between solute and solvent molecules
  • Temperature
• Deciding factors for solubility:

  • Nature of solute and solvent: 'Like dissolves like'
  • Temperature: solubility increases with temperature
  • Pressure: solubility of gas in liquid increases with pressure at a given temperature
  • Hydration energy: energy released when 1 mole of ions gets hydrated
• Methods of expressing Concentration of Solution:

  • Mass percentage (w/W)
  • Volume percentage (v/V)
  • Mass by volume percentage
  • Mole fraction
  • Molarity
  • Molality
  • Normality
  • Parts per million (ppm)
• Relationship between Molarity (M) and Molality (m):

  • Molality (m) = (Molarity × Density) / (1000 × Molar mass of solute)
• Henry's Law states that the mass of a gas dissolved in a liquid at a constant temperature depends on the pressure applied, with the partial pressure of the gas in vapor phase being proportional to the mole fraction of the gas in the solution
• To avoid the toxic effects of high nitrogen concentration in blood, scuba diving tanks are filled with air diluted with He (11.7%), N2 (56.2%), and O2 (32.1%)
• At high altitudes, low blood oxygen causes climbers to become weak and unable to think clearly, symptoms of a condition known as anoxia
• Limitations of Henry’s law:

  • Applicable only when the pressure of gas is not too high and the temperature is not too low
  • The gas should not undergo any chemical change
  • The gas should not undergo association or dissociation in the solution
• Key Terms:

  • Mole: The amount of substance containing the same number of elementary entities
  • Partial Pressure: Pressure exerted by a gas if it occupies the same volume in a mixture at the same temperature
  • Concentrated Solution: Solution with a relatively large amount of solute
  • Dilute Solution: Solution with a relatively very small amount of solute
• Raoult’s law for a solution of volatile liquids states that the partial vapor pressure of each component in the solution is directly proportional to its mole fraction
• Ideal Solution:

  • Obeys Raoult’s law over a wide range of concentration at a specific temperature
  • DmixH = 0
  • DmixV = 0
  • The force of attraction between A–A and B–B is nearly equal to A–B
• Positive deviation from Raoult’s law: A–B interactions are weaker than A–A or B–B interactions, leading to an increase in vapor pressure
• Azeotropes are binary mixtures with the same composition in liquid and vapor phases that boil at a constant temperature
• Minimum boiling azeotropes form in non-ideal solutions showing large positive deviation from Raoult’s law, like water and benzene
• Dalton’s law of partial pressure states that the total pressure exerted by a mixture of gases is the sum of the partial pressure of each individual gas present
• Colligative properties of solutions depend only on the number of particles of the solute in a definite volume of the solvent and include:

  • Relative lowering of vapour pressure
  • Elevation of boiling point
  • Depression in freezing point
  • Osmotic pressure
• Relative lowering of vapour pressure is the ratio of the lowering of vapour pressure to the vapour pressure of the pure solvent, equal to the mole fraction of the solute
• Elevation of boiling point occurs when the number of solute particles increases, leading to an increase in the boiling point of the solution
• Depression of freezing point is the decrease in freezing point when a non-volatile solid is added to the solvent, becoming equal to that of the pure solvent at a lower temperature
• Osmosis is the net flow of solvent from a solution of lower concentration to higher concentration through a semi-permeable membrane, while osmotic pressure is the extra pressure applied to stop this flow
• Abnormal molecular mass is when the calculated molecular mass using colligative properties differs from the theoretical molecular mass
• The van’t Hoff factor is the ratio of the observed value of a colligative property to the normal value of the same property
• Key Terms:

  • Normal boiling point: Temperature at which the vapor pressure of the liquid equals one atm
  • Molal boiling point: Boiling point of a 1 molal solution
  • Freezing point: Temperature at which the vapor pressure of liquid solvent equals the vapor pressure of solid solvent
  • Endosmosis: Inward osmosis of water into the semi-permeable membrane
  • Exosmosis: Outward osmosis of water from the cell membrane
  • Desalination: Conversion of sea water into potable water fit for drinking by reverse osmosis process
  • Plasmolysis: When a plant cell is placed in a hypertonic solution, causing the cell to shrink due to osmosis
• Electrochemistry involves the production of electricity from the energy released during a chemical reaction and the use of electrical energy to carry out chemical transformations
• An electrochemical cell, also known as a galvanic or voltaic cell, converts chemical energy into electrical energy
• Oxidation is when a substance loses one or more electrons, while reduction is when a substance gains electrons
• Redox reaction involves oxidation and reduction processes happening simultaneously
• In a galvanic cell, two half-cells containing electrodes dipped in an electrolytic solution are connected by a salt bridge
• The salt bridge completes the inner cell circuit, prevents the transfer of electrolyte between half-cells, and maintains the electrical neutrality of the electrolytes
• The standard hydrogen electrode (SHE) is a reference electrode used to determine the electrode potential of another half-cell connected to it
• The potential difference between the two electrodes of a galvanic cell is called the cell potential or electromotive force (emf) when no current is flowing through the circuit
• Factors affecting electrode potential include the nature of the metal or electrode, concentration of metal ions in solution, and temperature
• Standard electrode potential (E°) is the electrode potential at 25°C, 1 bar pressure, and 1 M solution
• The standard electrode potential of any electrode can be measured by connecting it to a reference electrode like the standard hydrogen electrode (SHE)
• The standard hydrogen electrode consists of a platinum electrode coated with platinum black, dipped in an acidic solution with pure hydrogen gas bubbled through it
• The cell potential, measured in volts, is the potential difference between the two electrodes of a galvanic cell
• The standard hydrogen electrode (SHE) is a redox electrode with zero standard electrode potential, forming the basis of the thermodynamic scale of oxidation-reduction potentials
• The SHE is used as a reference to determine the electrode potential of another half-cell connected to it and can act as both anode and cathode half-cells