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प्रश्न
A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
- Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
- Name the black substance formed and give its chemical formula.
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उत्तर
- Air contains traces of hydrogen sulphide (H2S) gas. It slowly reacts with silver present in the silver article to form silver sulphide (black in colour). A coating of silver sulphide (Ag2S) gets deposited on the surface of the metal. The phenomenon is known as corrosion. Tooth pastes generally contain traces of hydrogen peroxide as one of the constitutents. It reacts with silver sulphide to form silver sulphate which is white in colour. Therefore, whiteness is restored to the article.
- `underset("(Black)")("Ag"_2"S") + 4"H"_2"O"_2 -> underset("(White)")("Ag"_2"SO"_4) + 4"H"_2"O"`
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संबंधित प्रश्न
Corrosion can be prevented by using ……………. solution.
In the reaction represented by the equation:
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
(i) name the substance oxidised.
(ii) name the oxidising agent.
(iii) name the substance reduced.
(iv) name the reducing agent.
Explain oxidation in terms of gain or loss of oxygen with one example.
The process of respiration is:
(a) an oxidation reaction which is endothermic
(b) a reduction reaction which is exothermic
(c) a combination reaction which is endothermic
(d) an oxidation reaction which is exothermic
State, giving reason, whether the substances printed in bold letters have been oxidized or reduced.
H2S + Cl2→ 2HCl + S
Write the equation in the ionic form
CuSO4(aq) + Fe(s)→ FeSO4(aq) + Cu(s)
Divide the above equation into oxidation and reduction half-reactions.
Select the correct answer from the symbol in the bracket.
The element, which like hydrogen is a strong reducing agent.
Oxidising agents are also called as ______ because they remove electrons form other substances.
Which of the following statements about the given reaction are correct?
\[\ce{3Fe_{(s)} + 4H2O_{(g)} -> Fe3O4_{(s)} + 4H2_{(g)}}\]
(i) Iron metal is getting oxidised.
(ii) Water is getting reduced.
(iii) Water is acting as the reducing agent.
(iv) Water is acting as oxidising agent.
Oxidation is a process which involves ____________.
\[\ce{MnO2 + 4HCl -> + 2H2O + Cl2}\]
Identify the substance oxidized in the above equation.
Identify the oxidising agent (oxidant) in the following reactions
`"Pb"_3"O"_4 + 8"HCl" -> 3"PbCl"_2 + "Cl"_2 + 4"H"_2"O"`
Identify the oxidising agent (oxidant) in the following reactions
`2"Mg" + "O"_2 -> 2"MgO"`
Why do we store silver chloride in a dark coloured bottle?
Write a short note on oxidizing and reducing agents.
The sum of the oxidation number of all atoms in a compound is ______.
______ is a metal that has a high resistance to corrosion.
Choose the odd one out and write the reason:
Answer the questions based on the equation below:
\[\ce{CH3 - CH2 - OH ->[{[O]}][K2Cr2O7/H2SO4] CH3 - COOH}\]
- What type of reaction is it?
- What is the role of the chemical written on the arrow?
- Give one example of one such type of chemical as in answer (b).
