Question

In the equation, $Cu + xHN{O_3} \to Cu{(N{O_3})_2} + yN{O_2} + 2{H_2}O$ , the values of $x$ and $y$ are:
A. 3 and 5
B. 8 and 6
C. 4 and 2
D. 7 and 1

Answer 1

Hint: An equation is balanced when the same number of each element is represented on the reactant and product sides. Equations must be balanced to accurately reflect the law of conservation of matter. The stoichiometry is defined in a reaction only if all the atoms on the reactant side are balanced on the product side.

Complete step by step answer:
The reaction that has been provided to us here is:
$Cu + xHN{O_3} \to Cu{(N{O_3})_2} + yN{O_2} + 2{H_2}O$
Let us balance the atoms in the reaction one by one with respect to both the reactants and products.
(i) Copper ($Cu$ ): As we can see that the number of copper atoms are already balanced on the reactant and product side, there will be no change.
(ii) Hydrogen ($H$ ): As we can see from the reactant side that there are $x$ number of hydrogen atoms. Along with that there are 4 hydrogen atoms on the product side. This means that the value of $x$ should be 4. But along with that, we have to check the number of atoms of nitrogen and oxygen as well because on the reactant side, the hydrogen atoms are present in the nitric acid which is composed of nitrogen and oxygen as well. Mathematically, the equation can be written as:
$x = 4$
(iii) Nitrogen ($N$ ): If the value of $x$ is kept 4, the number of nitrogen atoms also becomes 4. On the other hand, the number of nitrogen atoms as ($2 + y$ ). Thus, the equation can be written as:
$2 + y = 4 \Rightarrow y = 2$

Thus, the correct option is C. 4 and 2.

Note:
Copper(II) nitrate, \[Cu{(N{O_3})_2}\] , is an inorganic compound that forms a blue crystalline solid. Anhydrous copper nitrate forms deep blue-green crystals and sublimes in a vacuum at\[\left( {150 - 200} \right)^\circ C\]. Copper nitrate also occurs as five different hydrates, the most common ones being the hemipentahydrate and trihydrate.