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Experiment 45: titration of sodium hydroxide solution with hydrochloric acid

Experiment 45: titration of sodium hydroxide solution with hydrochloric acid

Equipment:
  • Flat bottom flask
  • 50 mL volumetric pipette
  • Peleus ball
  • burette
  • Tripod material
  • Magnetic stirrer
  • Beaker
  • Stirring pig
  • funnel
  • Filter paper
  • safety goggles
Chemicals:
  • Caustic soda (concentration unknown)
  • Hydrochloric acid standard solution (c = 0.1 mol / L)
  • Bromothymol blue
Hazard warnings:
  • Caustic soda: corrosive R 34; S 26-36 / 37 / 39-45
  • Hydrochloric acid dil .: irritant R 36/37/38 S 2-28
Execution:
With the help of a volumetric pipette and a peleus ball, 50 mL of a sodium hydroxide solution of unknown concentration are pipetted out of a flat bottom flask and filled into a BG. This so-called template is placed on a magnetic stirrer and provided with a stirring pig; then a few drops of a bromothymol blue solution are added as a pH indicator. For better visibility of the color change, we can put a white filter paper under the BG. Using a funnel, fill a standard HCl solution into a burette attached to the stand up to the uppermost mark. (Usually the top marking on a burette is 0 mL, so that it is easier to read off the consumption of titrant.) We allow excess hydrochloric acid to drain into a BG. The stirrer is switched on and the titrant is now gradually trickled into the template up to the point where the indicator changes from blue to yellow. The consumption of hydrochloric acid is read on the burette. For a more accurate determination of the equivalence point (complete neutralization of the sodium hydroxide solution. In this experiment, the neutral and equivalence point culminate, since a strong base is titrated with a strong acid.) With the smallest possible error, the titration should be carried out several times and an average should be calculated. The first titration should initially be used to roughly define the transition area of ​​the indicator. In the next rounds, the hydrochloric acid is then only added drop by drop at the transition point in order to be able to read the most accurate value possible.


Fig. 3660 Sketch "titration of sodium hydroxide solution with hydrochloric acid" (SVG)
Observation:
50 mL hydrochloric acid are used up to the point where the indicator changes from blue to yellow.
Explanation:
Bromothymol blue changes at a pH of around 7. At this point there is a neutrally reacting sodium chloride solution, because the OH - ions of the sodium hydroxide solution have been neutralized by the H3O + ions of the hydrochloric acid: Since 1 mole of hydrochloric acid neutralizes exactly 1 mole of sodium hydroxide solution, the amount of moles of hydrochloric acid n (HCl) used corresponds exactly to the amount of moles of sodium hydroxide solution n (NaOH) provided. Thus, the concentration of the sodium hydroxide solution can be calculated using the relationship:
Reaction equation:
Remarks:
For example, Schweda & amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; Straehle.1 Riedel, among others, offers a legible outline of acid-base chemistry 2
Disposal:
A saline solution can be disposed of via the municipal sewage network without any problems.
Literature:
  1. Schweda, E. and J. Strähle (2005). Jander-Blasius: Introduction to the inorganic-chemical internship. Stuttgart, S. Hirzel Verlag. 15: 381-437.
  2. Riedel, E. (2004). Inorganic chemistry. Berlin, Walter de Gruyter. 6: 317-339.