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What is qualitative analysis in chemistry?
Qualitative analysis refers to the identification of the nature of a substance and its constituents, specifically identifying cations and anions in salts.
What are cations and anions?
Cations are positively charged ions contributed by bases, while anions are negatively charged ions contributed by acids.
Give an example of a cation and an anion from common salts.
In NaCl, Na+ is a cation and Cl- is an anion.
What is the macro analysis amount of substance used in qualitative analysis?
In macro analysis, 0.1 to 0.5 g of substance is used.
What is the purpose of preliminary examination in qualitative analysis?
Preliminary examination provides important information like color, smell, and solubility, which can simplify further analysis.
List three methods of qualitative analysis reactions perceptible to senses.
Formation of a precipitate, 2) Change in color, 3) Evolution of gas.
How can solubility of a salt suggest the nature of its ions?
An acidic or basic solution indicates hydrolysis of the salt and can suggest whether it is derived from weak or strong acids/bases.
What indicates a presence of carbonate ion during qualitative analysis?
Effervescence upon adding dilute H2SO4, which releases CO2 that turns lime water milky.
What do gases evolved during preliminary tests with dilute acids reveal?
They provide indications about the presence of certain anions such as carbonate or sulfide.
What does a white precipitate formation upon adding BaCl2 suggest about the solution?
It indicates the presence of sulfate ions (SO4 2–) when precipitate is formed that is insoluble in dilute and concentrated acids.
What is the result of treating sulfide ions with dilute H2SO4?
The presence of H2S gas, which smells like rotten eggs, indicating a sulfide ion's presence.
How is ammonia gas detected during the analysis of ammonium ion?
A strong ammonia smell is produced when NaOH is added to a sample containing ammonium ions.
What can a chocolate brown precipitate with potassium ferrocyanide indicate?
It indicates the presence of copper ions (Cu2+) when added to its solution.
What color changes occur with the presence of iron(II) and iron(III) during testing?
Iron(II) gives a pale green precipitate while iron(III) appears as reddish-brown.
How is magnesium ion confirmed during qualitative analysis?
Magnesium ion (Mg2+) is confirmed by the formation of a white precipitate of magnesium ammonium phosphate upon adding disodium hydrogen phosphate.
What chemical reaction occurs when testing for phosphate ions?
The addition of ammonium molybdate to a solution containing phosphate ions produces a canary yellow precipitate.
What precaution should be taken when using hydrochloric acid in qualitative analysis?
Always pour acid into water and never the other way around to avoid violent reactions.
Why is it essential to heat the solution during tests for Group-I cations?
Heating ensures that any potential precipitate forms correctly and is identified accurately.
What is the effect of passing H2S gas in qualitative analysis?
It helps in precipitating certain cations, indicating group classifications based on solubility.
What is 'aqua regia'?
Aqua regia is a mixture of concentrated hydrochloric and nitric acid used to dissolve noble metals.
