chem lab 2

chem lab 2

1. EXP 5

   • AIM: To estimate the amount of chloride in a water sample by Mohr’s method.
     • PRINCIPLE: It is an example of precipitation reaction.
       • AgNO3 + NaCl → AgCl + NaNO3 Ag+ + Cl- → AgCl
       • The completion of the reaction in this case is observed by employing potassium chromate (K2CrO4) solution as the indicator.
         • At the end point, the yellow colour changes into reddish brown due to the reaction
           • 2AgNO3 + K2CrO4 → Ag2CrO4 + 2KNO3
             • K2CrO4 indicator will not be precipitated as Ag2CrO4 until all the chlorides in the solution have been precipitated as AgCl.
       • Procedure
         • Titration I - Standardization of silver nitrate solution
           • 10ml of standard NaCl solution (N/20) is pipetted out into a clean conical flask.
             • 1ml of 2% K2CrO4 indicator is added to it. The solution turns yellow in color.
               • It is titrated against AgNO3 solution taken in the burette.
                 • During each addition of AgNO3, the content in the conical flask is shaken well.
                   • Near the end point, the discharge of red color will be slow and at the end point one drop will impart a light brownish red color to the solution which will not be discharged by further shaking.
         • Titration II: Estimation of Chloride
           • chloride solution is made up to 100 ml in a standard flask.
             • Exactly 10ml of this solution is pipetted out into a clean conical flask.
               • To this solution 1.0 ml of 2% K2CrO4 indicator is added.
                 • titrated against standardized AgNO3 solution from the burette.
                   • addition of AgNO3 solution is continued until the solution produced a reddish brown tinge.
         • RESULT: Amount of chloride present in the whole of the given solution is 0.0833 g / 100 mL.

2. EXP 6

3. EXP 7

   • Aim: To estimate the strength of the mixture of acetic acid and hydrochloric acid present in a given mixture by conductometrically.
     • Principle: The conductivity of the solution is related to the mobility of ions which in turn related with the size of the ions.
       • When a mixture of acids like a strong acid (HCl) and a weak acid (acetic acid) are titrated against a strong base (NaOH), strong acid reacts first followed by a weak acid.
         • When the titration of strong acid and strong base are carried out, there is a decrease in conductivity as highly mobilized hydrogen ions are replaced by sodium ions.
           • NaOH + HCl NaCl + H2O
             • When the whole strong acid is consumed, base reacts with weak acid and conductivity increases as unionised weak acid becomes the ionised salt.
               • CH3COOH + Na+ + OH- CH3COO- + Na+ + H2O
       • PROCEDURE: 10 ml of this made up solution is pipetted out into clean beaker and 100 ml of distilled water is added.
         • The conductivity cell is dipped into the test solution and titrated against NaOH (0.5 ml) interval with proper stirring.
           • The conductivity cell is dipped into the test solution and titrated against NaOH (0.5 ml) interval with proper stirring.
             • The conductance is measured after each 0.5 ml addition of NaOH at various stages of neutralization. After complete neutralization, the amount of acid present in the given mixture is determined based on the volume of NaOH consumed.
               • Volume of base consumed for strong acid and weak acid are determined by plotting a graph between conductance and volume of base added, where first end point corresponds to strong acid and second end point corresponds to weak acid.

4. EXP 8