Question

1g of copper powder was taken in a china dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equation of reactions, the name and the colour of the products formed in each case.

Answer 1

We have to know that metals react with oxygen to give basic oxides. Metallic oxides are basic in nature since they react with dilute acids to give salt and water. They also react with water to form metal hydroxides which are alkaline in nature because these metal hydroxides liberate $O{H^ - }$ ions in solution. We have to know that hydrogen reacts with metal oxides to form metal and water.

Complete step by step answer:
When we take 1g of copper powder in a china dish and heat it. We get a black coloured substance and the substance is copper oxide.
When copper reacts with oxygen, the product formed in copper oxide. We can write the chemical equation for this reaction as,
$2Cu\,\,\,\,\,\,\,\,\,\,\,\, + \,\,\,\,O\xrightarrow{{}}\,\,\,2CuO \\\ Copper\,\,\,\,\,\,\,\,\,Oxygen\,\,\,\,\,\,Copper\,oxide \\\$
We get copper oxide by the oxidation of copper.
The colour of copper is red brown.
The oxygen is obtained from air.
The colour of copper oxide is black.
When we pass hydrogen gas over the heated substance, that is copper oxide, we get the product as metallic copper. We can write the chemical equation for this reaction as,

$$\,\,\,2CuO\,\, + \,\,\,\,\,\,\,{H_2}\,\,\,\,\,\,\,\,\,\xrightarrow{{}}\,\,Cu\,\,\,\,\, + \,\,{H_2}O \\\ Copper\,\,\,\,\,\,Hydrogen\,\,\,\,\,\,\,\,\,\,\,Copper\,\,\,Water \\\ oxide\,\,\,\,\,\,\,\,\,\,\,\,\,\,gas\,\,\,\,\,\,\,\, \\\$$

The colour of copper oxide is black.
The colour of copper metal is red brown.
We get metallic copper by the reduction of copper oxide.

Note:
The reaction of non-metals with oxygen gives the product as non-metal oxides. They are acidic in nature and turn blue litmus to red. On dissolving in water, non-metals oxides form acids.
Example: When sulfur reacts with oxygen, sulfur dioxide is formed. The chemical reaction is written as,
$S + {O_2}\xrightarrow{{}}S{O_2}$
The nature of sulfur dioxide is acidic.
When sulfur dioxide is dissolved in water, a solution of sulfurous acid is formed. The chemical reaction is written as,
$S{O_2} + {H_2}O\xrightarrow{{}}{H_2}S{O_3}$
Sulfurous acid changes blue litmus to red, denoting that it is an acid.