Equivalent mass of a substance

Scheele, Lavoisier, and Priestley independently established that the loss of mass was caused by the evacuation of an element termed oxygen, followed by the recombination of the metal in the air. As a result, the equivalent mass of a substance that undergoes oxidation was coined.

When alchemists and mediaeval metallurgists tried to measure exactly how much iron was generated from the smelting of a certain amount of iron ore, they discovered that the solid iron’s weight was always less than the ore’s. The procedure was given the name equivalent mass of a substance that undergoes reduction because of the decrease in mass.

The process of losing and acquiring electrons takes place at the same time. The loss of one or more electrons by an atom is known as the equivalent mass of a substance that undergoes oxidation. The acquisition of one or more electrons by an atom is known as the equivalent mass of a substance that undergoes reduction. As a result, oxidation and reduction always occur simultaneously; we can only cognitively separate them. 

Types of the reduction reaction.

Combination, decomposition, displacement, combustion, and disproportionation are the five main types of an equivalent mass of a substance that undergoes reduction processes.

The equivalent mass of a substance that undergoes reduction reactions can be found all over the place. Redox processes underpin much of our technology, from fire to laptop batteries. Redox reactions (reduction-oxidation) occur when the equivalent mass of a substance that undergoes oxidation statuses of the reactants change. This happens because electrons are constantly moved between species in such interactions. Redox reactions can be simple, such as the combustion of carbon in oxygen to produce carbon dioxide (CO2), or more complex, such as the oxidation of glucose (C6H12O6) in the human body through a variety of electron transfer mechanisms.

The name “redox” is derived from two-electron transfer concepts: reduction and oxidation. The following are the definitions of these processes:

A molecule, atom, or ion equivalent mass of a substance undergoes oxidation when it loses electrons or increases its oxidation state.

A molecule, atom, or ion gains electrons or decreases its oxidation status as it is the equivalent mass of a substance that undergoes reduction.

“OIL RIG”—Oxidation Is Losing (electrons), Reduction Is Gaining—is a handy mnemonic for remembering these processes (electrons).

Redox reactions are matched sets: if one species is oxidised, another must be reduced in the same process. As we look at the five primary types of redox reactions: combination, decomposition, displacement, combustion, and disproportion, keep this in mind.

• Combination

Combination reactions bring together different components to create a chemical molecule. Oxidation and reduction occur in tandem, as is customary.

The equation in general: A+B→AB

The sum of the oxidation states in the reactants equals the sum of the oxidation states in the products: (2)(+1) + 0 + 0 (-2)

Because H2 and O2 are the molecular forms of their respective elements in this equation, their oxidation states are both zero. The final product is H2O, with oxygen having an oxidation state of -2 and hydrogen having an oxidation state of +1.

• Decomposition

Decomposition reactions are the reversal of combination reactions, in which a chemical molecule is broken down into its constituent atoms.

General equation: AB → A + B

Calculation: (2)(+1) + (-2) = 0 → 0 + 0

Water is “decomposed” in this equation into hydrogen and oxygen, both of which are neutral. H2O has a total oxidation state of 0, with each H having a +1 state and the O having a -2 state; consequently, breakdown oxidises oxygen from -2 to 0 and reduces hydrogen from +1 to 0.

• Displacement

Compounds and the “replacing” of elements are involved in displacement reactions, also known as replacement reactions. They can take the form of single or double replacement reactions.

General equation (single displacement): A + BC → AB + CA

One element in the reactants is “replaced” by another element in the products in a single replacement reaction.

Calculation: 0 + [(+1) + (-1) = 0] →→ [(+1) + (-1) = 0] + 0

In this equation, Cl is reduced and replaces Br, while Br is oxidised.

General equation (double displacement): AB + CD → AD + CB

A double replacement reaction is similar to a single replacement reaction in that two elements in the reactants are “replaced” by two elements in the products.

In this equation, Fe and H as well as O and Cl trade places.

• Combustion

Oxygen and organic fuel are always present in combustion reactions. We can observe methane combustion to release energy in the image below.

The general equation of a combustion reaction is:

CxHy+(x+y4)O2→xCO2+y2H2O

• Disproportionation

Substances can be both oxidised and reduced in some redox processes. Disproportionation reactions are what they’re called. The reaction of hydrogen peroxide, H2O2, when poured over a wound is a real-life illustration of such a process. Because hydrogen peroxide decomposes to create oxygen and water, this may appear to be a simple decomposition reaction at first:

2 H2O2(aq) → 2 H2O(l) + O2(g)

However, the oxidation states of oxygen are the key to this reaction. It’s worth noting that both the reactant and the products contain oxygen. The oxidation state of oxygen in H2O2 is -1. Its oxidation state in H2O is -2, indicating that it has been reduced. However, the oxidation state of O2 is 0, indicating that it has been oxidised. This is a disproportionation reaction because oxygen has been both oxidised and reduced in the reaction. This reaction takes the following broad form:

2A → A’ + A”

Conclusion

Redox reactions, also known as oxidation-reduction processes, are reactions in which electrons are transferred from one species to another. An oxidised species loses electrons, while a reduced species obtains electrons. Redox reactions can be identified using oxidation numbers, which are assigned to atoms in molecules based on the assumption that all links between them are ionic. During a reaction, an increase in the oxidation number refers to oxidation, whereas a drop relates to reduction.