Practical Chemistry

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A cation is a positively charged ion (loses electrons), while an anion is a negatively charged ion (gains electrons). Normal salts are made up of both a cation and an anion.

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Original Solution (O.S.) is a homogeneous mixture of salt and solvent prepared before performing cation tests. It is necessary because cations are identified by chemical reactions with alkalis or spec…

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Ammonia gas: (1) Turns red litmus blue, (2) Gives white fumes with moist HCl gas (NH₃ + HCl → NH₄Cl), (3) Turns Nessler's reagent brown. It evolves when ammonium salts are heated with NaOH.

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CO₂ gas: (1) Turns lime water milky [CO₂ + Ca(OH)₂ → CaCO₃ + H₂O], (2) Milkiness disappears with excess CO₂ [CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂], (3) Shows no effect on potassium dichromate or KMnO₄ soluti…

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Chlorine gas (greenish-yellow): (1) Blue litmus turns red and is finally bleached, (2) Turns starch iodide paper blue-black [2KI + Cl₂ → 2KCl + I₂, then I₂ + Starch → Blue colour]. It's liberated when…

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Hydrogen gas: (1) Burns with a 'pop' sound when brought near a burning splinter [2H₂ + O₂ → 2H₂O], (2) Neutral to litmus, (3) Burns with pale blue flame. It's evolved when reactive metals react with a…

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HCl gas (pungent choking odour): (1) Blue litmus turns red, (2) Gives dense white fumes with ammonia [HCl + NH₃ → NH₄Cl], (3) Gives curdy white precipitate with AgNO₃ [HCl + AgNO₃ → AgCl + HNO₃].

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H₂S gas (rotten egg smell): (1) Blue litmus turns red, (2) Turns lead nitrate paper black [Pb(NO₃)₂ + H₂S → PbS + 2HNO₃], (3) Turns moist lead acetate paper black. It's evolved when sulphide salts rea…