Question

Write answers to the following.
a. What is the reaction called when oxidation and reduction take place simultaneously? Explain with one example.
b. How can the rate of the chemical reaction, namely, decomposition of hydrogen peroxide be increased?
c. Explain the term reactant and product giving examples.
d. Explain the types of reaction with reference to oxygen and hydrogen. Illustratre with examples.
e. Explain the similarity and difference in two events, namely adding NaOH to water and adding CaO to water.

Answer 1

a. The process in which oxidation and reduction occurs simutaneously is called as redox reaction.

• Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
• Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

For example: If we add stannous chloride solution to the yellow solution of ferric chloride then light green ferrous chloride solution and stannic chloride solution are produced.

$2FeC{l}_3\left(aq\right)+SnC{I}_2\left(aq\right)\to 2FeC{l}_2\left(aq\right)+SnC{I}_4\left(aq\right)$

Before the reaction, 3Cl atoms were attached to each iron atom. After the reaction, only two chlorine atoms are attached. That is one negative chlorine atom is released. Therefore, reduction of FeCl₃ happened or this reactor on the other hand, before reaction two chlorine atoms where attached with each atom of tin (stannum). Due to the above reaction the number of chlorine attached to tin atom increases to four. That is, oxidation of SnCl₂ has taken place. Therefore, in this reaction oxidation of one substance and reduction of another substance take place simultaneously. This is called redox reaction.

b.The rate of decomposition of hydrogen peroxide can be increased by having the reaction occurs in the presence of iodide ion. The reaction is proceed by two step mechanism:

$$\begin{gathered} Step1:H_2{O}_2\left(aq\right)+I^{-}\left(aq\right)\to H_{2}O\left(l\right)+I{O}^{-}\left(aq\right) \\ Step2:I{O}^{-}\left(aq\right)+H_2{O}_2\left(aq\right)\to H_{2}O\left(l\right)+O_2\left(g\right)+I^{-}\left(aq\right) \end{gathered}$$

c.
Reactant: The substance which take part in a chemical reaction are called reactants.
Product: the substance which forms as a result of chemical reaction is called products.
The new substance produced as a result of chemical reaction is called products.
For example: When two sodium atoms react with two chlorine atoms(reactants), they give a completely new compound (product) i.e. sodium chloride (two atoms).
$2Na+C{l}_2\to 2NaCl$

d.
There are main three types of chemical reactions with reference to oxygen and hydrogen:
1.Combination Reaction
When two atoms react to form a compound, it is know as combination reaction.
For example: $2H_2+O_2\to 2H_{2}O$

2. Decomposition Reaction
When a compound breaks into simple molecular substances from which it is made up of, it is know as decomposition reaction.
For example: $2H_{2}O\to 2H_2+O_2$

3. Oxidation and reduction reaction:
Oxidation:
(i) The addition of oxygen to a substance is called oxidation.
(ii) The removal of hydrogen to a substance is called oxidation.
Reduction:
(i) The addition of hydrogen to a substance is called reduction.
(ii) The removal of oxygen to a substance is called reduction.
For example: $CuO+H_2\to Cu+H_{2}O$
In the above reaction, copper oxide is changing to Cu. That is, oxygen is being removed from copper oxide. So, copper oxide is being reduced to copper.
In the above reaction, H₂ is changing into H₂O. That is , oxygen is being added to hydrogen. So, hydrogen is being oxidised to water.

e.
Chemical equations involved:

$$\begin{gathered} 1)NaOH(s)+H_{2}O(l)\to Na⁺(aq)+OH⁻(aq)+\Delta (HEAT) \\ 2)CaO\left(s\right)+H_{2}O\left(l\right)\to Ca\left(OH\right)₂\left(aq\right)+\Delta \left(HEAT\right) \end{gathered}$$
Similarities:
1) Both of the equations are exothermic. It means a lot of heat is evolved during the reaction.
2) Both reaction form strong basic solution.
Differences :
1) Sodium Hydroxide is strong base dissociates to form Na⁺ and OH⁻ ion. While Calcium oxide added water to form Calcium Hydroxide which further dissociates.
2) NaOH is a monoacidic base. and CaO is a Di-Acidic base.
3) NaOH, CaO should be added to water gradually with constant stirring.CaO on reacting with water produces basic solution called as Calcium hydroxide which is used for white washing and this reaction is more dangerous as compare to NaOH.