VPB 112: General Veterinary Biochemistry (1+1)

CONCENTRATION OF SOLUTIONS

• Solutions may be regarded as mixtures of substances viz. the solute and the solvent. The substance that is dissolved is ‘Solute’ and the medium that dissolves the solute is called ‘Solvent’. The particle size of the solute in solvent is < 1 nm.
• The concentration of the solution refers to the amount of the solute present in the given quantity of the solvent or solution.
• The relative concentrations of the substances in a solution can be measured in several ways:
  • Percentage Concentration (%)
  • Parts per million (ppm)
  • Molarity (M)
  • Molality (m)
  • Normality (N)

Percentage Concentration (%)

• This represents parts per 100 i.e. Number of parts of the solute present in 100 parts of the solution. It is denoted by %. There are three ways of expressing Percentage Concentration (%) – W/V, W/W and V/V.
• Examples
  • W/V (Weight / Volume): To prepare 9% Saline solution W/V, weigh 9 grams of NaCl and dissolve in 100 ml of distilled water.
  • W/W (Weight / Weight): To prepare 5 % Sugar solution W/W, weigh 5 grams of Glucose and dissolve in 100 grams of distilled water.
  • V/V (Volume / Volume): To prepare 25% ethanol, take 25 ml of ethanol and add 75 ml of distilled water, making the total volume to 100 ml.

Parts per million (ppm)

• This refers to the number of parts of the solute present in 1 million (10 lakhs) parts of the solution. It is denoted as ppm.
• Example: 10 ppm chlorine means 10μg of chlorine in 1 g of water. i.e. 1 ppm = 1μg/g or 1μg/ml or 1 mg/Litre.

Molarity (M)

• It is defined as the number of moles of the solute dissolved per litre of the solution. It is denoted by M; Units: moles / L (smaller units mM / L, μM / L etc.)
  • M= Gram molecular weight of the solute / Litre of the solution                        
• Example:
  • The Molecular Weight of NaCl is 58.5. To prepare 1 M NaCl solution, weigh 1 g molecular weight of NaCl i.e. 58.5 g and dissolve in distilled water to make a final total volume of 1 litre.

Molality (m)

• It is defined as the number of moles of the solute dissolved per Kg of the solution. It is denoted by m; Units: moles / Kg (smaller units mM / Kg, μM / Kg etc.)
  • M= Gram molecular weight of the solute / Kg of the solution                        
• Example:
  • The Molecular Weight of NaCl is 58.5. To prepare 1 m NaCl solution, weigh 1 g molecular weight of NaCl i.e. 58.5 g and dissolve in 1000 grams or 1 Kg of distilled water.

Normality (N)

• It is defined as the number of equivalent weight of the solute dissolved per litre of the solution. It is denoted by N; Units: Eq/ L (smaller units mEq / L, μEq / L etc.)
  • N= Gram equivalent weight of the solute / Litre of the solution
• One-gram equivalent weight of an element or a compound represents its capacity to combine or replace One mole of hydrogen. In general,
  • Eq. Wt = Molecular Weight  / Positive (‘+’) Valences of the Constituent ions                  
• Example
  • The molecular weight of Sodium Carbonate (Na₂CO₃) is 106 and equivalent weight is 53. To prepare 1 N Na₂CO₃ solution_, weigh 53 g of it and dissolve in 1000 ml or 1 Litre of distilled water.