Preparation and analysis of a complex metal salt

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Experiment 7

Preparation and analysis of a complex metal salt  (15-12-2006)

Objective

  1. To prepare a sample of copper-ammonia complex salt.
  2. To determine the ammonia content in the sample of salt.
  3. To determine the metal content of the sample of salt.

Results

  1. Determination of ammonium content

HCl was added in excess into the complex salt. The NH3 ligands were protonated to NH4+ and were detached from the metal cation. The volume of HCl in excess was determined by titration using NaOH. The ammonium content of the salt was determined.

  • Weight of the complex salt used: (6.321 – 5.896) = 0.425g
  • Volume of HCl (0.6M) added onto the flask: 25cm3

No. of moles of HCl added: 25/1000 x 0.6 = 0.015 moles

  • The reaction of the titration is given by the following chemical equation:

HCl + NaOH → NaCl + H2O

(1) Volume of NaOH (0.5M) used in the titration: 20.8 – 4.3 = 16.5 cm3

(2) No. of moles of NaOH used: 16.5 / 1000 x 0.5 = 8.25 x 10-3 moles

(3) No. of moles of HCl in excess = No. of moles of NaOH used in titration = 8.25 x 10-3 moles

  • No. of moles of HCl reacting with NH3: 0.015 – 8.25 x10-3 = 6.75 x 10-3 mole

  • By the equation NH3 + HCl → NH4Cl,

Number of moles of NH3 in the sample of salt = no. of moles of HCl = 6.75 x 10-3 mole

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  • Molar mass of NH3 : 14 + 1 x 3 = 17 g/mole
  • The mass of NH3 in the sample = 17 x 6.75 x 10-3 = 0.11475 g
  • % by mass of NH3 in the sample = 0.11475 / 0.425 x 100% = 27.0% 

  1. Determination of metal content

Part B was repeated except that no indicator was added this time. The solution was kept at pH 10 and the solution was diluted. EDTA titration was carried out after the solution was heated to 60oC. Eriochrome Black T was used as an indicator. ...

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