Question

define double displacement reaction and give one example of each of the following types of this reaction in which (i) a precipitate is formed
(ii) a black precipitate is formed
(iii) a gas is liberated
(iv) white precipitate is formed


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Answer 1

Answer:

Double Displacement Reaction : Two different atoms or ions are exchanged in double displacement reaction .

Answer 2

Double Displacement reaction: A double displacement reaction is a reaction that takes place between two ionic compounds and where an exchange of ions takes place.

General Form: A regular double displacement reaction is of the form:

A⁺X⁻ + B⁺Y⁻ -----------> A⁺Y⁻ + B⁺X⁻

Precipitation Reaction: It is a reaction in which a precipitate (in soluble mass which settles down at the bottom of the test-tube/beaker is called a precipitate) is formed. For example,

K₂SO₄             + BaI₂       -------------->   2KI                 +         BaSO₄↓

Potassium         Barium                       Potassium              Barium

Sulphate           Iodide                        Iodide                      Sulphate

                                                                                            (white ppt.)

(Mobile users or users with a small screen can refer to the attachment 1)

In the above reaction, a white-colored precipitate BaSO₄ is formed whose presence is denoted by the ↓ arrow besides it.

A reaction in which a black precipitate is formed:

When Hydrogen sulphide gas is passed through copper (II) sulphate, a black precipitate of copper (II) sulphide along with sulphuric acid is formed.

H₂S           +    CuSO₄    ------------>   H₂SO₄      +     CuS↓

hydrogen      Copper (II)                   sulphuric       copper (II)

sulphide         sulphate                    Acid                Sulphide

                                                                                (black ppt.)

(Mobile users or users with a small screen can refer to the attachment 3)

A reaction in which a gas is liberated: A gas is liberated when

1. A metal reacts with an acid.
2. A metal carbonate reacts with an acid.
3. A substance is burnt in presence of oxygen etc.

Some examples are:

C + O₂ -------> CO₂

2Na + 2HCl ------> 2NaCl + H₂

2NaHCO₃ ------heat------> Na₂CO₃ + H₂O + CO₂

Na₂CO₃ + 2HCl ------> 2NaCl + H₂O + CO₂

(Mobile users or users with a small screen can refer to the attachment 2)

A reaction in which a white ppt. is formed:

K₂SO₄             + BaI₂       -------------->   2KI                 +         BaSO₄↓

Potassium         Barium                       Potassium              Barium

Sulphate           Iodide                        Iodide                      Sulphate

                                                                                            (white ppt.)

(Mobile users or users with a small screen can refer to the attachment 1)

In the above reaction, a white-colored precipitate BaSO₄ is formed.