Experiment 7
Preparation and analysis of a complex metal salt (15-12-2006)
Objective
- To prepare a sample of copper-ammonia complex salt.
- To determine the ammonia content in the sample of salt.
- To determine the metal content of the sample of salt.
Results
- 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