Lecture
Equipment and reagents: test tube rack, spirit lamp, test tube holder, aqueous solutions of acetic and hydrochloric acids, copper(II) oxide, solutions of alkali and baking soda, zinc (granules), indicator solutions, indicator paper. For the additional experiment — various fruits and berries.
Procedure
Carry out the reaction of acetic and hydrochloric acids with the substances provided to you. Compare the observed phenomena. Write the equations of the reactions taking place in molecular and ionic form.
Additional experiment
Test the juices of lemon, apple, cranberry, and other acidic fruits with litmus solution, methyl orange, and indicator paper. Confirm the presence of acids in their composition.
To investigate the chemical properties of carboxylic acids (using acetic acid as an example) and compare them with the chemical properties of inorganic acids (using hydrochloric acid as an example).
Test tube rack
Spirit lamp
Test tube holder
Aqueous solutions of acetic and hydrochloric acids
Copper oxide (CuO)
Solutions of alkali (NaOH) and baking soda (Na₂CO₃)
Zinc (Zn, granules)
Indicators: litmus, methyl orange, universal indicator paper
Juices of lemon, apple, cranberry, and other acidic fruits (for the additional experiment)
Observation:
When zinc is added to acetic acid, gas is released (slowly).
When zinc is added to hydrochloric acid, gas is released vigorously.
Reaction equations:
Molecular:
CH₃COOH + Zn → (CH₃COO)₂Zn + H₂↑
2HCl + Zn → ZnCl₂ + H₂↑
Ionic:
2CH₃COOH ⇌ 2CH₃COO⁻ + 2H⁺
Zn + 2H⁺ → Zn²⁺ + H₂↑
2H⁺ + Zn → Zn²⁺ + H₂↑
Observation:
Acetic acid slowly dissolves the black precipitate of copper oxide.
Hydrochloric acid does so quickly and with a vivid change in the color of the solution.
Reaction equations:
Molecular:
2CH₃COOH + CuO → (CH₃COO)₂Cu + H₂O
2HCl + CuO → CuCl₂ + H₂O
Ionic:
2H⁺ + CuO → Cu²⁺ + H₂O
Observation:
Both acids react with alkali, forming salts and water.
Molecular:
CH₃COOH + NaOH → CH₃COONa + H₂O
HCl + NaOH → NaCl + H₂O
Ionic:
H⁺ + OH⁻ → H₂O
Observation:
In both cases gas (CO₂) is released, especially vigorously with HCl.
Molecular:
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑
2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂↑
Ionic:
2H⁺ + CO₃²⁻ → H₂O + CO₂↑
Procedure:
Apply a drop of juice to indicator paper and to solutions of litmus and methyl orange.
Observation:
Lemon juice: indicator paper turns red, litmus turns red, methyl orange turns pink
Apple juice: similar, but less acidic
Cranberry juice: strong change, bright red color
Conclusion:
Fruits and berries contain organic acids (citric, malic, etc.), which is confirmed by the reaction with indicators.
Similarities:
Both acetic acid and hydrochloric acid react with metals, bases, oxides, and carbonates, forming salts.
Both exhibit acidic properties.
Differences:
Hydrochloric acid is a strong acid (fully dissociates), while acetic acid is weak (partially dissociates).
Reactions with the inorganic acid proceed faster and more vigorously.
Conclusion from the additional experiment:
Fruits contain organic acids, as evidenced by the reactions with indicators.
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