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pH Meter and Measurement of Various Solutions

Hazards

HCl and NaOH are corrosive and toxic.

Chemicals and Solutions

  • Sodium carbonate, 0.1 M (basic solution)
  • Sodium acetate, 0.1 M (basic solution)
  • Ferric nitrate, 0.1 M (acid solution)
  • Hydrochloric acid, 0.01 M (acidic solution)
  • Sodium hydroxide, 0.01 M (basic solution)

Materials

  • pH meter
  • Combination pH electrode
  • Digital readout voltmeter and pH interface
  • Leads to connect pH meter, interface, and voltmeter
  • Kimwipes
  • Polyethylene wash bottle of distilled water
  • 6 - 150 ml beakers
  • 400 ml beaker for waste

Procedure

  1. Electrode must remain in distilled water when not in use.
  2. After each measurement, rinse electrode with distilled water.

Discussion

In the dissociation of sodium carbonate, carbonate anion reacts with water to give OH- thereby forming a basic solution:

\( \ce{ CO3^2- + H2O -> HCO3- + OH- } \)

Similarly, in the dissociation of sodium acetate, acetate ion reacts with water to form OH-, thereby also giving a basic solution:

\( \ce{ CH3COO- + H2O -> CH3COOH + OH- } \)

The hydrated ions of metals of small radius and high charge, like Fe3+ are stronger acids than water and donate protons to water molecules. The ferric nitrate solution is acidic:

\( \ce{ Fe(H2O)6^3+ + H2O -> Fe(H2O)5(OH)^2+ + H3O+ } \)

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