On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed.
(a) Write a balanced chemical equation of the reaction.
(b) Identity the brown gas X evolved.
(c) Identity the type of reaction.
(d) What could be the nature of aqueous solution of the gas X?

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Solution

Chemical Equations
The symbolic representation of a chemical reaction is given by a chemical equation. A chemical equation is balanced by adding coefficients to reactants and products such that the number of atoms of each element is equal on the reactant side and the product side. The states of reactant and products are also mentioned in the balanced equation. A chemical equation is used to determine the identity of the products formed and its relative mass.
(a) Balanced equation for the reaction
When powdered Copper(II) nitrate [Cu(NO₃)₂] is heated, Copper oxide (CuO) is formed with the evolution of Oxygen gas (O₂) and Nitrogen dioxide (NO₂). The balanced equation for the reaction is:
$2 C u {(N O_{3})}_{2} \overset{Δ}{\to} 2 C u O (s) + O_{2} (g) + 4 N O_{2} (g)$
(Copper (Copper (Oxygen) (Nitrogen
nitrate) oxide) dioxide)
(b) Identity of brown gas
When Copper (II) nitrate is heated, Nitrogen dioxide gas is evolved which has a brown color.
Therefore, the unknown gas X evolved during the reaction is Nitrogen dioxide.
(c) Type of reaction
A reaction in which a single reactant forms more than one product is called a decomposition reaction. In the given reaction, Copper (II) nitrate, on heating, gives three products.
Therefore, the given reaction is an example of a decomposition reaction. Copper (II) decomposes to Copper oxide, Oxygen and Nitrogen dioxide.
(d) Nature of solution
The Nitrogen dioxide formed during the reaction dissolves in water to form Nitrous acid (HNO₂) and Nitric acid (HNO₃). The chemical equation for the dissolution can be given as:
$2 N O_{2} (g) + H_{2} O (l) \to H N O_{2} (a q) + H N O_{3} (a q)$
(Nitrogen (Water) (Nitrous acid) (Nitric acid)
dioxide)
The Nitrous acid and Nitric acid in the solution reduces the pH of solution to below 7.
Therefore, a solution of gas X will be acidic.

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On heating blue-colored powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas, and a brown gas X are formed

(a) Write a balanced chemical equation of the reaction.
(b) Identity the brown gas X evolved.
(c) Identity the type of reaction.
(d) What could be the pH range of the aqueous solution of the gas X?

Question 39

On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed

(a) Write a balanced chemical equation of the reaction.
(b) Identity the brown gas X evolved.
(c) Identity the type of reaction.
(d) What could be the pH range of aqueous solution of the gas X?

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