Advertisements
Advertisements
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.
Advertisements
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"`
APPEARS IN
संबंधित प्रश्न
Define corrosion.
Explain the following in terms of gain or loss of oxygen with one example:
Oxidation
In the reaction represented by the following equation:
\[\ce{CuO_{(s)} + H2_{(g)} -> Cu_{(s)} + H2O_{(l)}}\]
- name the substance oxidised
- name the substance reduced
- name the oxidising agent
- name the reducing agent
In the context of redox reactions, the removal of hydrogen from a substance is known as ______.
The process of respiration is ______.
Fill in the blank
In redox reaction oxidation and reduction occur ............................
TRUE \ FALSE
Hydrogen is a good oxidizing agent.
Give the general group study of hydrogen with reference to
reducing power
State whether the following conversion is oxidation or reduction:
K → K+ + e-
State whether the following conversion is oxidation or reduction:
2Cl- - e-→ Cl2
Explain the term redox reaction with an example involving the reaction of hydrogen sulphide with chlorine.
State what is reducing agent. Give an example of oxidising agent in the gaseous, liquid, and solid form.
Give two tests for a reducing agent.
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.
Identify the oxidising agent (oxidant) in the following reactions.
`"CuO" + "H"_2 -> "Cu" + "H"_2"O"`
Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid whereas copper does not. Explain why?
Mention some oxidation reactions that occur in daily life.
The sum of the oxidation number of all atoms in a compound is ______.
Identify the following reactions as oxidation/reduction/redox reaction
2Mg +O2 → 2MgO
