To identify compounds, we have to follow some steps in chemistry. Qualitative analysis teaches us how to identify one compound from other compound.
We do our testing for anions and cations. Different cations show different characteristics. Also anions are also show like that. In this tutorial, we will learn, these things in detail. At the end of the tutorial you should try to explain how a compound is identified from another compound by following what you learnt in qualitative analysis.
In this section, we are going to identify anions when cation is common in other compounds.
Both of Na2S and Na2SO4 are solutions and also colourless. Therefore we cannot identify it by colour. Sodium ion is common for both compounds. So we have to test the anions sulfide ion S2- and sulfate ion (SO42-).
Add BaCl2 to both solutions separately. We can see a white precipitate forms in a one solution (Na2SO4 solution). That precipitate is BaSO4. But BaS is soluble in water and colourless too.
NaCl and NaBr are white solids. Sodium ion is common in both NaCl and NaBr. Also both NaCl and NaBr are soluble in water and cannot see a precipitate to identify a compound.
With AgNO3, NaCl and NaBr gives AgCl and AgBr precipitates respectively.
Here, we are going to study about, how to identify a cation from another cation when anion is common in those compounds.
Both sodium and potassium are alkali metals. NaCl and KCl are colorless aqueous solutions. So we cannot see a color change in two compounds and unable to identify NaCl from KCl from colors of solution.
Na+ and K+ give yellow and purple colors respectively for flame test.
Answer is 2. Anhydrous sodium carbonate is white.
M is a cation which exists as a nitrate compound in an aqueous solution. Part of this solution is separated and H2S gas is sent. Then a black precipitate is given. Next, another part of this M's nitrate solution is separated. When NaOH is added, white precipitate is given. With excess NaOH, white precipitate dissolve and give colourless solution. What could be the cation?
PbS is a black precipitate. See all inorganic metal sulfide precipitates and solubility.
Pb(OH)2 is a white precipitate. See all inorganic metal hydroxide precipitates and solubility.