8.3 Identification of ions by chemical and spectroscopic means (Triple)
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Describe the test for carbonate anions
Add dilute acid, e.g. HCl Fizzing observed, as CO2 is released. E.g. Na2CO3 + 2 HCl → 2 NaCl + H2O + CO2
Describe the test for sulfate anions
Add a solution containing Ba2+ cations, e.g. a solution of BaCl2 White precipitate of BaSO4 forms E.g. K2SO4+ BaCl2 → 2 KCl + BaSO4
Describe the test for halide anions
Add a solution of AgNO3 (acidified with HNO3) Chlorides - white precipitate, silver chloride; Ag+ + Cl− → AgCl Bromides - cream precipitate, silver bromide; Ag+ + Br−→ AgBr Iodides - yellow precipitate, silver iodide; Ag+ + I− → AgI
What are instrumental methods?
They are accurate, sensitive and rapid methods which are useful when the amount of sample is very small
Describe the flame emission spectroscopy
• Instrumental method used for identifying metal ions in solution or measuring their concentration • Spectroscope measures the exact wavelength of the light emitted by a metal ion • That allows for definite identification - sometimes colours are difficult to distinguish. • Concentrations are found by measuring the intensity of light emitted. The more intense light, the greater the concentration of the metal ion in a solution. • From the intensity vs concentration graph, you can read off a relevant concentration value at a given intensity.
What are cations and anions?
Cations are the positive ions; anions are the negative ions.