science blog

  Pauly’s test is a biochemical test for the detection of tyrosine and histidine where the reagent couples with amines, phenols, and imidazole groups. The test was discovered by and is named after the German Chemist Hermann Pauly. Pauly’s test is a specific test for proteins containing tyrosine and histidine as the reagent undergoes diazotization with aromatic groups. The reaction is performed under cold conditions as the diazonium compound can only form at cold temperatures. The test is a specific test for proteins, which is performed for further differentiation between amino acids and proteins. Principle                    ❖   Pauly’s test is based on the principle of coupling between the amino acids and the diazonium ion formed in the reagent. The pauly’s reagent consists of sulphanilic acid dissolved in concentrated hydrochloric acid. The sulfanilic acid undergoes diazotization in the presence of sodium nitrate and hydr...

  Experiment:   Find out the Rheochor value of the given organic liquid. Molar mass (or Molecular weight) of the given liquid is 46.   Theory: Newton Friend showed that if molecular volume (or molar volume) of a liquid be multiplied by the eighth root of the coefficient of viscosity, it leads to a constant called rheochor., denoted by r.                           R = (M/D ) h 1/8 D is density of the liquid and M its molar volume Rheochor may be regarded as the molar volume of a liquid at the temperature at which its viscosity is unit.   Apparatus:   Ostwald’s viscometer, stop-watch, specific gravity bottle, rubber tube, screw type pinch cock, iron stand etc.   Procedure:   ·          Take an Ostwald’s viscometer and fix it in a stand in upright position. · ...

  Experiment: Determine the Viscosity of a liquid at room temperature by viscometer.   Theory:   Viscosity is a characteristic property of all fluids. The internal resistance of a liquid to its flow is called viscosity. Viscosity can be explained if a liquid is considered to consist of concentric layers which slide past one another when a liquid flows. Resistance to flow is regarded as an internal friction between the different layers of a liquid. So viscosity is a property of liquids by virtue of which it tends to oppose the relative motion between different layers of the liquid. Viscosity of a liquid is expressed in terms of Coefficient of Viscosity. Coefficient of Viscosity is defined as the force (in dynes) per unit area (one square centimeter) required to maintain unit difference of velocity between two parallel layers in the liquid, unit distance (one centimeter) apart. It is denoted by h (eta).   Units of Viscosity (Coefficient of Viscosi...

  Experiment: Determine the percentage composition of unknown liquid by surface tension method.   Apparatus: Stalagmometer, specific gravity bottle, screw type pinch cock, beakers, rubber tube, balance, stand etc. Procedure: The composition of this mixture can be determined as follows:   ·          Prepare various compositions of the two liquids (water and a miscible organic liquid)   Sample No.                 1           2           3           4           5           6 Org. liquid (%)             100       80    ...