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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
What is an oxidation reaction? Identify in the following reaction (i) the substance oxidised, and (ii) the substance reduced:
ZnO + C → Zn + CO
In the following reaction between lead sulphide and hydrogen peroxide:
PbS (s) + 4H2O2(aq) → PbSO4(s) + 4H2O(1)
(a) which substance is reduced?
(b) Which substance is oxidised?
Fill in the following blanks with suitable words:
The addition of hydrogen to a substance is called ........ whereas removal of hydrogen is called .......
Fill in the blank
In redox reaction oxidation and reduction occur ............................
Explain the following in term Reduction of gain or loss of oxygen with two example.
Identify from the following reaction the reactants that undergo oxidation and reduction.
\[\ce{2Ag2O → 4 Ag + O2 \uparrow}\]
Compare hydrogen with alkali metals on the basis of:
Oxide formation
Give the general group study of hydrogen with reference to
burning
Describe briefly the ionic concept of oxidation and reduction. Give an equation to illustrate.
Is it essential that oxidation and reduction must occur side by side in a chemical reaction? Explain
State, giving reason, whether the substances printed in bold letters have been oxidized or reduced.
PbO + CO → Pb + CO2
Write the equation in the ionic form
CuSO4(aq) + Fe(s)→ FeSO4(aq) + Cu(s)
A metal oxide that is reduced by hydrogen is
Name:
a solid that is an oxidizing agent.
State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.
State the condition and give balanced equation for the conversion of coke to water gas.
Find the oxidation number of the elements in the following compounds.
- C in CO2
- Mn in MnSO4
- N in HNO3
Identify the reducing agent in the following reactions
`2"H"_2 + "O"_2 -> 2"H"_2"O"`
Identify the oxidising agent (oxidant) in the following reactions.
`"CuO" + "H"_2 -> "Cu" + "H"_2"O"`
It is recommended to use air tight containers for storing oil for a long time.
