Classify Na Cl, Fe, Conc. H₂SO₄, table salt sodium carbonate crystals based on the following characteristics when exposed to atmosphere.
(i) Gain in mass
(ii) Loss in mass
(iii) No change in mass on exposure to atmosphere
Answers
Following observations are made in relation to mass on exposing NaCl, Fe, Conc. H₂SO₄, table salt and sodium carbonate crystals to atmosphere :
i) Gain in mass - Fe, conc. H₂SO₄, table salt
ii) Loss in mass - sodium carbonate crystals
iii) No change in mass - NaCl
• A substance on exposure to atmosphere can either absorb or lose moisture, or remain unaffected by it.
• Depending on its nature, the substance undergoes either a gain or loss in weight, or undergoes no change at all.
• NaCl - Pure NaCl neither absorbs nor loses mositure on exposure to atmosphere, therefore, undergoes no change is mass.
• Fe - Iron metal on being exposed to atmosphere for a long period of time, combines with oxygen and water vapour present it.
• This process is called rusting of iron (Fe₂O₃.nH₂O), and there is a gain in mass when iron is exposed to atmosphere.
• Conc. H₂SO₄ - Conc. H₂SO₄ is hygroscopic in nature, means, it absorbs moisture from atmosphere without getting dissolved in it.
• Therefore, a gain in mass is observed on exposing conc. H₂SO₄ to atmosphere.
• Table Salt - Table salt contains MgCl₂ or CaCl₂ as impurities which are hygroscopic in nature.
• These impurities absorb mositure from atmosphere and the table salt undergoes a gain in mass on being exposed to atmosphere.
• Sodium carbonate crystals - The chemical formula for sodium carbonate crystals is Na₂CO₃.10H₂O.
• These crystals are efflorescent in nature and lose their water of crystallisation on being exposed to atmosphere.
• Therefore, a loss in mass is observed.