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Q18:
Why do we apply paint on iron articles?
Solution :
1. Theoretical Foundation: The Mechanism of Corrosion
The application of paint on iron articles serves as a protective measure against corrosion, specifically the process known as rusting. Iron ($Fe$) reacts spontaneously with atmospheric oxygen ($O_2$) and moisture ($H_2O$) to form hydrated iron(III) oxide ($Fe_2O_3 \cdot xH_2O$).
The chemical reaction is represented as follows:
$4Fe(s) + 3O_2(g) + 2xH_2O(l) \rightarrow 2Fe_2O_3 \cdot xH_2O(s)$
[Per the Principles of Redox Chemistry, iron acts as the reducing agent and oxygen as the oxidizing agent in this electrochemical process.]
2. The Protective Mechanism of Painting
Painting functions as a physical barrier method. By coating the surface of the iron, the paint creates an impermeable layer that prevents the contact of the metal substrate with the surrounding environment.
- Exclusion of Reactants: The paint layer blocks the diffusion of oxygen molecules to the iron surface.
- Moisture Sealing: It prevents water vapor or liquid water from reaching the iron, thereby inhibiting the electrolytic medium required for the corrosion cell to function.
- Prevention of Rust Propagation: Without the electrochemical circuit (anode: $Fe \rightarrow Fe^{2+} + 2e^-$; cathode: $O_2 + 2H_2O + 4e^- \rightarrow 4OH^-$), the oxidation of iron is halted at the interface.
3. Visual Representation of Corrosion Inhibition
4. Comparative Summary of Protective Measures
| Method | Mechanism | Primary Utility |
|---|---|---|
| Painting | Physical barrier application | Structural iron/steel, aesthetics |
| Galvanization | Sacrificial protection via Zinc | Industrial piping, outdoor hardware |
| Greasing/Oiling | Hydrophobic film formation | Moving machine parts |
Final Solution: We apply paint on iron articles to create a physical barrier that prevents the metal from coming into contact with atmospheric oxygen and moisture, thereby arresting the chemical process of corrosion (rusting) and extending the structural integrity and lifespan of the iron.
More Questions from Class 10 Science Chemical Reactions and Equations EXERCISES
- Q1: Which of the statements about the reaction below are incorrect? $2PbO(s) + C(s) \rightarrow 2Pb(s) + CO_2(g)$ (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced.
- Q2: The reaction is an example of a $Fe_2O_3 + 2Al \rightarrow Al_2O_3 + 2Fe$
- Q3: What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
- Q4: What is a balanced chemical equation? Why should chemical equations be balanced?
- Q5(a): Translate the following statements into chemical equations and then balance them. (a) Hydrogen gas combines with nitrogen to form ammonia.
- Q5(b): Translate the following statements into chemical equations and then balance them. (b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
- Q5(c): Translate the following statements into chemical equations and then balance them. (c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
- Q5(d): Translate the following statements into chemical equations and then balance them. (d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
- Q6(a): Balance the following chemical equations. (a) $HNO_3 + Ca(OH)_2 \rightarrow Ca(NO_3)_2 + H_2O$
- Q6(b): Balance the following chemical equations. (b) $NaOH + H_2SO_4 \rightarrow Na_2SO_4 + H_2O$
- Q6(c): Balance the following chemical equations. (c) $NaCl + AgNO_3 \rightarrow AgCl + NaNO_3$
- Q6(d): Balance the following chemical equations. (d) $BaCl_2 + H_2SO_4 \rightarrow BaSO_4 + HCl$
- Q7(a): Write the balanced chemical equations for the following reactions. (a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
- Q7(b): Write the balanced chemical equations for the following reactions. (b) Zinc + Silver nitrate → Zinc nitrate + Silver
- Q7(c): Write the balanced chemical equations for the following reactions. (c) Aluminium + Copper chloride → Aluminium chloride + Copper
- Q7(d): Write the balanced chemical equations for the following reactions. (d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
- Q8(a): Write the balanced chemical equation for the following and identify the type of reaction in each case. (a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
- Q8(b): Write the balanced chemical equation for the following and identify the type of reaction in each case. (b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
- Q8(c): Write the balanced chemical equation for the following and identify the type of reaction in each case. (c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
- Q8(d): Write the balanced chemical equation for the following and identify the type of reaction in each case. (d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
- Q9: What does one mean by exothermic and endothermic reactions? Give examples.
- Q10: Why is respiration considered an exothermic reaction? Explain.
- Q11: Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
- Q12: Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
- Q13: What is the difference between displacement and double displacement reactions? Write equations for these reactions.
- Q14: In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
- Q15: What do you mean by a precipitation reaction? Explain by giving examples.
- Q16(a): Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation
- Q16(b): Explain the following in terms of gain or loss of oxygen with two examples each. (b) Reduction
- Q17: A shiny brown coloured element ‘$X$’ on heating in air becomes black in colour. Name the element ‘$X$’ and the black coloured compound formed.
- Q19: Oil and fat containing food items are flushed with nitrogen. Why?
- Q20(a): Explain the following terms with one example each. (a) Corrosion
- Q20(b): Explain the following terms with one example each. (b) Rancidity
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