Question

Write chemical equation for the following reactions:
a.) Calcium metal reacts with water.
b.) Cinnabar is heated in the presence of air.
c.) Manganese dioxide is heated with aluminium powder.

Answer 1

Hint: In order to solve the given problem and find the chemical equation for the reactions first we will see the chemical symbol or molecular formula for each of the compounds given in their general name. Further we will see the chemical reaction and will write the balanced chemical equation for each of the given reactions.

Complete step by step solution: i. Calcium metal reacts with water.
We know that chemical representation of calcium is $Ca$
Water is the common name used for the compound with molecular formula ${H_2}O$
Now let us see the balanced chemical equation for the given reaction.
$Ca + 2{H_2}O \to Ca{\left( {OH} \right)_2} + {H_2}$
From the above equation we can see when calcium reacts with water hydrogen and calcium hydroxide are formed as the product of the reaction.
ii. Cinnabar is heated in the presence of air-
As we know that cinnabar is the common name for mercurous sulphate and the molecular formula for cinnabar is $HgS$
Given that cinnabar is heated in the presence of air so it will react with oxygen ${O_2}$
The balanced chemical equation for the given chemical reaction is:
\[HgS + 3{O_2} \to 2HgO\mathop \to \limits^\Delta 2Hg + {O_2}\]
From the above chemical equation it is clear that the product formed is mercurous oxide which on heating splits into mercury and oxygen. So in this reaction mercury is obtained from cinnabar.
iii. Manganese dioxide is heated with aluminium powder-
The molecular formula for manganese dioxide is given as $Mn{O_2}$ . And the aluminium powder can be chemically represented as $Al$
Now let us see the balanced chemical equation for the given reaction.
$3Mn{O_2} + 4Al \to 3Mn + 2A{l_2}{O_3}$

From the above chemical equation it is clear that manganese dioxide reacts with aluminium powder to give manganese and aluminium oxide as the products.

Note: In order to solve such problems related to chemical equations and chemical reactions students must remember the general name and molecular formula for certain chemical compounds. Students after writing the reaction must cross check if the equation is balanced or not.