Question

Mention briefly the various units used to represent the composition of a solution. Also mention the effect of temperature on each of them.

Answer 1

1. Mass Percentage or Percentage by Mass (w/w): Mass percentage is defined as the mass of the solute in grams dissolved per 100 g of the solution. It is also referred to as weight percentage (w/w). 
   Mathematically, 
   `"Mass percentage of solute" = "Mass of solute"/("Mass of solute" + "Mass of solvent") xx 100`
   Both solute and solution masses remain constant with temperature.
2. Volume Percentage or Percentage by Volume (v/v): Volume percentage is defined as the volume of a solute (in a particular unit) present in the 100 units of the volume of the solution.
   Mathematically,
   `"Volume percentage of solute" = "Volume of solute"/"Volume of solution" xx 100`
   Volume changes with temperature due to expansion or contraction.
3. Grams Per Litre (g/L): The concentration of a solution in grams per litre refers to the amount of solute in grams present in one litre of the solution.
   Grams per litre is temperature-dependent because the volume of the solution changes with temperature, affecting the calculated concentration.
4. Molarity (M): The number of moles of solute dissolved per litre of the solution at a particular temperature is called the molarity of the solution at that temperature.
   Mathematically,
   `"Molarity" = "Number of moles of the solute"/"Volume of the solution in litres"`
   Thus, molarity actually represents the concentration of a solution in mol L^−l.
   A solution's molarity varies with temperature because molarity involves volume, which is temperature sensitive. Only at a specific temperature does a solution have a given molarity value.
5. Formality (F): The number of gram formula mass of an ionic solute dissolved per litre of the solution at a particular temperature is called formality of the solution. Thus,
   `"Formality of solution" = "Number of gram formula mass of the solute"/"Volume of the solution in litres"`
   Formality of a solution is a function of temperature and changes with a change in temperature.
6. Molality (m): Molality of a solution is defined as the number of moles of solute dissolved per 1000 g (1 kg) of the solvent.
   Molality actually represents the concentration of a solution in mol kg^−l.
   Mathematically,
   `"Molality" = "Number of moles of solute"/"Mass of the solvent in kg"`
   Since the mass of the solvent is independent of temperature, the molality of the solution does not change with temperature.
7. Normality (N): The number of gram equivalents of the solute dissolved per litre of a solution at a particular temperature is called the normality of the solution.
   normality actually expresses the concentration of a solution in gram equivalents per litre (g eq L⁻¹).
   Mathematically,
   `"Normality" = "Number of gram equivalents of solute"/"Volume of solution in litres"`
   Normality of a solution is also a function of temperature and varies with change in temperature.
8. Mole Fraction (χ): The mole fraction of a particular component in a solution is the ratio of the number of moles of that component to the total number of moles of all the components present in the solution.
   Mathematically,
   `"Mole fraction of a component" = "Number of moles of the given component"/"Total number of moles in the solution"`
   Mole fraction is independent of temperature.
9. Parts per Million (ppm): The parts per million of a solute is the mass of the solute present in 10⁶ (one million) parts by mass of the solution.
   Mathematically,
   `"ppm of a solute" = "Mass of solute"/"Mass of solution" xx 10^6`
   It is temperature dependent.