EXPERIMENT: Add a 1/2 cup of vinegar and a teaspoon of table salt and stir. Drop...

EXPERIMENT: Add a 1/2 cup of vinegar and a teaspoon of table salt and stir. Drop 15 pennies into the solution for 10 to 15 minutes. Pull them out and allow them to dry by themselves on a towel. After setting them out for a while, the pennies should turn blue.

QUESTIONS

1. Vinegar is an acid that allowed the copper metal to be oxidized to copper (II) ion. Is copper metal becoming copper (II) ion an oxidation or a reduction? How do you know?

2. When pennies coated with copper (II) ion were renoved from the solution and set out in the air, the copper (II) ion on the penny combined with oxygen gas from the air to produce the blue product that you observed. What is the blue product? Write its formula.

3. Write the reaction showing copper (II) (aq) + oxygen gas -> blue product

Expert Solution

Pennies before cleaning looks dirty because copper ions react with oxygen to form Copper oxide which is dull/black colored. When acetic acid and salt(chloride) are used, the copper oxide layer is washed off and the pennies are cleaned.

a) In this reaction, Copper is converted to Cu⁺²

This is given by the equation : Cu ------------------> Cu⁺² + 2e^-

This is an oxidation reaction because the metal loses electrons and gets reduced and this reaction is termed as oxidation.

b) When Cu⁺² ions were removed and set out in the air without rinsing, the Cu⁺² ions on penny combine with oxygen from air and chlorine from salt to form a blue product called malachite

Formula of malachite is Cu₂CO₃(OH)₂ or CuCO₃.Cu(OH)₂. It is blue- greenish color

Cu⁺²_(aq)+ O_2(g)

Action of vinegar on copper(Cu) forms Copper acetate

Cu exists in +2 state in Copper acetate. Copper acetate is given by CH₃COOCu

2Cu + O₂ <------------> 2CuO

CuO + 2CH₃COOH -------------> Cu(CH₃COO)₂ + H₂O

2Cu(CH₃COO)₂ + O₂ -------------> CuCO₃.Cu(OH)₂

queen_honey_blossom answered 2 years ago

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