standardize a given sample of silver nitrate and to determine the chloride concentration of an unknown solution.
...olution Procedures: 1. 25mL of the given sodium chloride was pipetted into a conical flask. About 1mL of potassium chromate was added. 2. The solution was titrated against the given silver nitrate solution in burette. 3. The end pointed was reached when the first permanent reddish tinge was apparent. 4. The titration was repeated twice. 5. The blank titration was carried out. 6. 1mL of the potassium chromate was added to 50mL of water. 7. The solution was then titrated against silver nitrate from burette until end-point was reached. 8. The above titration was repeated, using the unknown chloride instead of sodium chloride. 9. The molarity of the silver nitrate and the chloride concentration in the unknown solution was calculated. Results: Titration I: silver nitrate against sodium chloride Trial 1 2 3 Blank 2nd burette reading (final reading) 19.95 40.00 21.00 37.35 1st burette reading (initial reading) 0 19.95 1.00 36.90 Vol. Of nitrate used 19.95 20.05 20.00 0.55 Vol. Of nitrate used in corrected vol. 19.45 19.55 19.50 Average volume of nitrate used = 19.50mL Titration II: Silver nitrate against unknown chloride Trial 1 2 3 Blank 2nd burette reading 31.05 38.05 31.70 37.35 1st burette reading 0 7.1 0.70 36.90 Vol. Of nitrate used 31.05 30.95 31.00 0.55 Vol. Of nitrate used in corrected vol. 30.55 30.45 30.50 Average volume of nitrate used = 30.50mL Calculations: Molarity of the silver nitrate = 25 x 0.0419.50 = 0.513M Let the mass of: KCl = y g KBr = (6-y) g 30.50 x 0.5131000 = 0.025 [y74.5 + 6-y119 ] x = 2.4372 ≈ 2.4 So the mass of KCl in the solution is 2.4g while that of KBr is 6 - 2.4 = 3.6g Mass concentration of KCl = 2.4 g/dm3 Discussion: In this experiment, the silver nitrate used was standardized before it can be used to undergo titration. This is because this nitrate is photosensitive. It would be broken down under light. Its concentration decreases with time and this is why it must be standardized every time before it is used. Also the nitrate is stored in brown bottles to reduce the amount of light that can get inside to dissociate the nitrate to minimum. In the two titrations, potassium chromate was used as an indicator. The silver ions would first react with the chloride or bromide ions in the solution. When all of the halide ions were neutralized, the silver ions would begin to react with the chromate ions and start to form a red precipitate. The appearance of the precipitate can ind...