Question

Create/draw a clear and organized FLOWCHART for K+, Fe+2 or Fe+3, Ni+2, Cr+3, NO3- and PO4-3. Discuss observations for any precipitate/color changes, what you would see if it was or wasn't there, etc.

Answer 1

For salt analysis, there is an organized , stepwise procedure to be followed in order to determine the anionic and cationic radicals present in the compound.
To determine the anionic radicals:
Step 1: To 0.1 g of the salt in a test tube a few drops of dilute sulphuric acid are added the mixture is gently warmed. Observe for any change or evolution of gas. If no gas is evolved, it confirms the absence of Carbonate (CO₃^-2 ), sulphide (S^2–), sulphite ( SO₃^-2 ), nitrite ( NO₂^-1) and acetate (CH₃COO^–) ions.
Step 2: To 0.1 g of the salt in a test tube a few drops of conc. H₂SO₄ are added the mixture is gently warmed. Observe for any change or evolution of gas.
If reddish brown fumes evolve, NO₃^-1 may be present. The fumes are due to evolution of NO₂ gas and become more dense on heating the mixture. If copper turnings are added to the mixture, the solution turns blue.
Confirmatory test of NO₃^-1 ions : Brown ring test.
To the salt solution add a freshly prepared solution of FeSO₄.  Then, conc. H₂SO₄ is addedalong the sides of the test tube without shaking. A dark brown ring is formed at the junction of the two solutions which confirms the presence of NO₃^-1 ions.
Step 3: If no gas is evolved on addition of dil. H₂SO₄ or conc. H₂SO₄, then SO₄^-2 or PO₄^-3 ions may be present.
For these tests we use the sodium carbonate extract of the compound which is prepared by boiling a mixture of salt and Na₂CO₃ in distilled water for 10 min.and then cooling and filtering. The filtrate is the sodium carbonate extract of the compound.
Test for PO₄^-3:
Add conc. HNO₃ to the sodium carbonate extract and warm. Then add ammonium molybdate solution and boil the mixture. Formation of a yellow precipitate confirms the presence of PO₄^-3 ions.
For analysis of the cationic radicals:
Step 1 : Observe the colour of the salt.
Fe⁺² salts are light green.
Fe ⁺³ salts are yellow or brown.
Ni⁺² salts are bright green.
Step 2: Flame test.
This test is usually done if the salt is coloured.
Take a paste of the salt in conc. HCl on a clean platinum wire and heat in a flame of the bunsen burner and observe the colour of the flame.
Although potassium salts are white, but they give a lilac colour flame .
Step 3: Prepare the O.S (original solution) of the salt in distilled water and warm it. Dil. HCl is added to dissolve the salt completely.
For identification of basic radicals they have been divided into groups.
Test for Fe⁺² or Fe⁺³ and Cr⁺³:
These ions belong to group III.  To the original solution and add a few drops of conc, HNO₃, and boil.. Add some solid solid NH₄Cl and boil again. Then after cooling the solution add excess of ammonium hydroxide and mix well.
A reddish brown ppt. indicates the presence of Fe³⁺ ions.
A greenish ppt. indicates the presence of Cr³⁺ ions.
Test for Ni⁺² :
Ni⁺² belong to group IV of basic radicals. When H₂S gas is passed through the solution of group-III, the appearance of a black precipitate indicates the presence of Ni⁺² or Co⁺² ions.
If the solution fom group III is shaken with a few drops of dimethyl glyoxime formation of a bright red precipitate confirms the presence of Ni²⁺ ion.