Solutions

• Solutions are homogeneous mixtures of two or more components where the component present in the largest quantity is the solvent, determining the physical state of the solution, while the other components are solutes
• Binary solutions consist of two components, where the solvent determines the physical state of the solution
• Types of solutions:

  • Gaseous Solutions: mixture of oxygen and nitrogen gases
  • Liquid Solutions: oxygen dissolved in water
  • Solid Solutions: solution of hydrogen in palladium
• Concentration of solutions can be described qualitatively as dilute or concentrated, or quantitatively using methods like mass percentage, volume percentage, mass by volume percentage, parts per million, and mole fraction
• Mass percentage (w/w) is defined as the mass of a component in the solution divided by the total mass of the solution, multiplied by 100
• Volume percentage (V/V) is defined as the volume of a component in the solution divided by the total volume of the solution, multiplied by 100
• Mass by volume percentage is commonly used in medicine and pharmacy, representing the mass of solute dissolved in 100 mL of the solution
• Parts per million (ppm) is used to express trace quantities of solute in a solution, calculated as the number of parts of the component divided by the total number of parts of all components of the solution, multiplied by 10^6
• Mole fraction (x) is defined as the number of moles of a component divided by the total number of moles of all components in the solution
• Molarity (M) is the number of moles of solute dissolved in one litre of solution, calculated as moles of solute divided by the volume of the solution in litres
• Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a specified temperature
• Solubility depends on the nature of solute and solvent as well as temperature and pressure
• Effect of temperature on solubility:

  • The solubility of a solid in a liquid is significantly affected by temperature changes
  • If the dissolution process is endothermic, the solubility should increase with a rise in temperature; if it is exothermic, the solubility should decrease
• Effect of pressure on solubility:

  • Pressure does not have a significant effect on the solubility of solids in liquids because solids and liquids are highly incompressible
  • For gases dissolved in liquids, the solubility of gases increases with an increase in pressure
• Henry's Law:

  • At a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid or solution
  • The most commonly used form of Henry’s law states that “the partial pressure of the gas in the vapour phase is proportional to the mole fraction of the gas in the solution” and is expressed as: p = KH x
• Henry's law constant (KH) values for N2 and O2 increase with temperature, indicating that the solubility of gases decreases with temperature
• Aquatic species are more comfortable in cold waters as the solubility of gases increases with decrease of temperature
• Applications of Henry's law include increasing CO2 solubility in soft drinks by sealing bottles under high pressure and explaining the dangers of high concentrations of dissolved gases for scuba divers
• To calculate the moles of N2 gas dissolved in 1 litre of water at 293 K with a partial pressure of 0.987 bar and KH of 76.48 kbar, use the formula: n = (partial pressure of N2 gas / KH) * volume of water
• The solubility of gas is related to the mole fraction in aqueous solution, calculated using Henry's law
• For a binary solution of two volatile liquids, Raoult's law states that the partial vapour pressure of each component is directly proportional to its mole fraction in the solution
• Total vapour pressure over a solution varies linearly with the mole fraction of a component, affecting the composition of the vapour phase in equilibrium with the solution
• Vapour pressure of chloroform (CHCl3) and dichloromethane (CH2Cl2) at 298 K are 200 mm Hg and 415 mm Hg respectively
• Total moles = 0.47 + 0.213 = 0.683 mol, mole fraction of CH2Cl2 = 0.47 / 0.683 = 0.688, mole fraction of CHCl3 = 1.00 – 0.688 = 0.312
• Using the mole fractions, calculate the total vapour pressure of the solution: ptotal = p1

  0 + (p2

  0 – p1

  0) x2 = 200 + (415 – 200) × 0.688 = 200 + 147.9 = 347.9 mm Hg
• Mole fractions in the gas phase: yCH2Cl2 = 285.5 mm Hg / 347.9 mm Hg = 0.82, yCHCl3 = 62.4 mm Hg / 347.9 mm Hg = 0.18
• Raoult's law states that the vapour pressure of a solution decreases when a non-volatile solute is added to a volatile solvent
• Colligative properties are properties of solutions that depend on the number of solute particles, regardless of their nature, relative to the total number of particles present in the solution
• The elevation of boiling point in a solution is directly proportional to the molal concentration of the solute in the solution
• The concept of attachment involves a strong reciprocal emotional bond between an infant and a primary caregiver
• Schaffer and Emerson's 1964 study on attachment aimed to identify stages of attachment and find a pattern in the development of attachment between infants and parents
• Participants in the study were 60 babies from Glasgow, and the procedure involved analyzing interactions between infants and carers
• Findings from the study indicated that babies of parents or carers who displayed 'sensitive responsiveness' were more likely to have formed an attachment
• In the context of chemistry, the molal concentration of the solute in a solution is crucial
• The molality, denoted as m, is the number of moles of solute dissolved in 1 kg of solvent
• The constant of proportionality, Kb, is called the Boiling Point Elevation Constant or Molal Elevation Constant
• To determine the molar mass of a solute, a known mass of solute in a known mass of the solvent is taken, and the change in boiling point (∆Tb) is determined experimentally
• The freezing point of a solution is lowered compared to that of the pure solvent due to the lowering of vapor pressure caused by the presence of a solute
• The decrease in freezing point, denoted as ∆Tf, is directly proportional to molality, m, of the solution
• The proportionality constant, Kf, known as the Freezing Point Depression Constant or Molal Depression Constant, depends on the nature of the solvent