In our daily life, we use many substances, including food items like lemon, orange, curd, milk, table salt, etc. These can be classified into acids, bases, and salts.
We will discuss acid base and salt definitions in
detail with some examples.
Table of Content
1. Definition of acid-base and salt
2. Arrhenius theory of acid and base
3. Bronsted -Lowry concept of acids and bases
4. Lewis concept of acids and bases
5. Acid bases and salt important questions
6. FAQs
What is the definition of acid-base and salt?
Acid
The term acid comes from the Latin term ‘acere’ or ‘acidus’
which means “sour’.
So, acids-
i.
Taste sour
ii.
Are corrosive
iii.
Change blue litmus to red
Base
The substances which have the following characteristics are
classified in base.
Bases are also called ‘alkali’ which
means ‘ash of plant’
· Alkali
– The bases which dissolve in water are called such as NaOH, KOH. So, all bases
are not alkali.
Bases-
i.
Has a bitter taste
ii.
Have a soapy feeling
iii.
Change red litmus to blue
Salt
Salts are basically ionic compounds that have anion
and cation and are formed when acids and bases react with each other. The reaction
is called the neutralization reaction.
Acid + base = salt + water
Salts –
i.
Have a high melting point
ii.
Are generally found in crystal form
These are the basic definitions of acids, bases, and salts but some other definitions of acids, bases, and salts are
following –
1. Arrhenius
theory of acid and base
2. Bronsted
-Lowry concept of acids and bases
3.
Lewis concept of acids and bases
1. Arrhenius
theory of acid and base
According to the Arrhenius theory, an acid is a substance
that gives hydrogen ion (`H^+`) when decomposes in water and the substances that decompose in water
and give hydroxyl ion OH- are called bases.
`HCl_{(aq)} \rightarrow H^+ + Cl^-`
`HNO_{3(aq)}\rightarrow H^+ + NO3^-`
`H_2SO_{4(aq)}\rightarrow H^+ + SO_4^(-2)`
`CH_3COOH_{(aq)}\rightarrow H^+ + CH_3COO^-`
`H_2CO_{3(aq)} \rightarrow H^+ + CO_3^-`
All above are acids because they give `H^+` ions in an aqueous
solution. But some acids get completely ionized, they are strong acids and
some acids do not ionize completely, they are called weak acids.
`KOH_{(aq)} \rightarrow K^+ + OH^-`
`NaOH_{(aq)} \rightarrow Na^+ + OH^-`
`Ca(OH)_{2(aq)} \rightarrow Ca^(+2) + 2OH^-`
`NH_4OH_{(aq)} \rightarrow NH4^+ + OH^-`
All above are bases because they give hydroxyl ions in an aqueous
solution. Those bases which get completely ionized are called strong bases and
the other bases which get partially ionized are called weak bases
Limitations of Arrhenius theory
Arrhenius theory of acids and bases is only useful for that substances that have hydrogen and hydroxyl ions. But the substances without
hydrogen and hydroxyl ions can not be determined by this theory.
2. Bronsted
Lowry concept of acids and bases
According to
Bronsted Lowry, acids are proton donors and bases are proton acceptors. This concept
describes conjugate acids and conjugate bases.
`HA + B \rightarrow A^- + HB^+`
Acid base conjugate conjugate
base acid
(`HA-A^-`) is called acid -conjugate base pair and (`B-HB^+`)
is called base- conjugate acid pair.
`H_2O + NH_3 ⇌ NH_4^+ + OH^-`
In the above
reaction, water is a proton donor, so it is an acid. It gives proton and changes
into corresponding base OH- called conjugate base and ammonia is a proton acceptor
so it is a base and it accepts proton and changes into NH4+ which is conjugate
acid.
So,(` NH_4^+ -NH_3`) and( `H_2O-OH^-`) are conjugate acid-base pairs.
Limitations of Bronsted Lowry theory
This theory is
not applicable to aprotic acids and bases like `SO_2`, `BF_3`,` CO_2`, etc.
3. Lewis
concept of acids and bases
Acids are the
substances that accept electron pair and bases are the substances that donate
electron pair.
So electron pair acceptors are acids and electron pair
donors are bases.
According to the theory, the electron-deficient compound works
like acid and is called Lewis acid
Compounds whose octet is incomplete
and cations are Lewis acids.
Examples of Lewis
acids
`AlCl_3`, `BF_3`, `Mg^2+`, `Na^+`
Electron rich compound work like base
and is called Lewis base
Examples of Lewis bases
`H_2O`, `NH_3`, `OH^-`,`Cl^-`
Limitations of Lewis concept of acids and bases
1. This theory is only applicable to those substances that form coordination compounds but HCl, `H_2SO_4` do not form coordination compounds.
2. It does not include the relative strength of acids and bases.
Acid bases and salt important questions
Q1. What is the amphoteric nature of water?
Ans. – Water has the ability to act as
both an acid and a base so it amphoteric in nature. In chemistry, substances
are classified into acidic, basic, and natural nature.
Q2. Why does the water show amphoteric nature?
Ans.
On the basis of Bronsted Lowry's concept water is amphoteric due to its ability to donate or accept protons (H+ ions),
water shows both properties
Water can donate a proton to the other substance
and acts as an acid.
`H_2O + NH_3\rightarrow NH_4^+ + OH^-`
(acid)
On the other hand, water accepts a proton and acts as a base
`H_2O + HCl → H_3O^+ + Cl^-`
(base)
That’s why water is amphoteric in nature.
Q3. Is salt made when an acid and bases are mixed?
Ans. – Yes, salt and water are
produced when an acid and base are mixed.
Q4. How did Arrhenius
define an acid and a base
Ans. - Arrhenius defined an acid as a hydrogen
ion producer and a base as a hydroxyl ion producer in an aqueous solution.
FAQs
1. When an acid and a base react what is produced?
Ans. – Salt and water are produced when an acid and a base react.
2. Do acid-base reactions always produce water?
Ans. – Yes, Generally acid-base reactions produce water.
3. What do bases produce in a reaction?
Ans.
4. Do bases react with metals?
Ans. – Yes, bases can react with metals in the reaction.
5. When Arrhenius theory was introduced?
Ans. – Arrhenius
theory was introduced in 1887
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