Lecture
1. Obtain a gas and prove its presence, using:
2. Using the scheme given, obtain a metal hydroxide and prove that it reacts with acids:
3. From the reagents provided to you, obtain an insoluble carbonate:
Prove that it reacts with hydrochloric acid.
4. Test solutions of the following salts with universal indicator:
Compare and explain the results of the investigation.
5. Prove that the solution given to you contains the salt:
In your report, present the reaction equations in molecular, full ionic, and net ionic forms.
Reaction:
Molecular equation:
Zn + 2HCl → ZnCl₂ + H₂↑
Observation: A colorless gas (hydrogen) is evolved, accompanied by hissing.
Proof: Bringing a lit splint close — a "pop test" (a small pop sound) occurs — a sign of hydrogen.
Reaction:
Molecular equation:
CaCO₃ + 2HCl → CaCl₂ + CO₂↑ + H₂O
Observation: Vigorous gas evolution occurs.
Proof: Passing the gas through limewater:
CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O — turbidity of the limewater confirms the presence of carbon dioxide.
Scheme:
MgCl₂ + 2NaOH → Mg(OH)₂↓ + 2NaCl
Next:
Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O
Observation: The white precipitate dissolves in the acid — proof that Mg(OH)₂ reacts with the acid.
Scheme:
CuCl₂ + 2NaOH → Cu(OH)₂↓ + 2NaCl
Next:
Cu(OH)₂ + 2HCl → CuCl₂ + 2H₂O
Observation: The blue precipitate dissolves — a neutralization reaction.
CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2NaCl
CaCO₃ + 2HCl → CaCl₂ + CO₂↑ + H₂O
Observation: The precipitate dissolves, and gas — CO₂ — is evolved.
ZnCl₂ + Na₂CO₃ → ZnCO₃↓ + 2NaCl
ZnCO₃ + 2HCl → ZnCl₂ + CO₂↑ + H₂O
AlCl₃ — undergoes hydrolysis, pH < 7 (acidic medium)
Explanation:
Al³⁺ + 3H₂O ⇌ [Al(H₂O)₆]³⁺ ⇌ Al(OH)₃ + 3H⁺ — acidification of the medium.
KCl — neutral salt, pH ~ 7
Molecular:
FeCl₃ + 3NaOH → Fe(OH)₃↓ + 3NaCl
Full ionic:
Fe³⁺ + 3Cl⁻ + 3Na⁺ + 3OH⁻ → Fe(OH)₃↓ + 3Na⁺ + 3Cl⁻
Net ionic:
Fe³⁺ + 3OH⁻ → Fe(OH)₃↓
Observation: A red-brown precipitate — proof of the presence of Fe³⁺ ions.
Molecular:
CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2NaCl
Full ionic:
Ca²⁺ + 2Cl⁻ + 2Na⁺ + CO₃²⁻ → CaCO₃↓ + 2Na⁺ + 2Cl⁻
Net ionic:
Ca²⁺ + CO₃²⁻ → CaCO₃↓
Observation: A white precipitate — confirmation of the presence of Ca²⁺ ions.
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