NOTE ON ACID and BASE THEORY.

THEORY OF ACID AND BASE.

In our next class, we will discuss the calculation part.

First, let us begin with the definitions of acids and bases.

You should know that we have many different definitions for an *ACID* and a *BASE*

These different definitions were proposed by different scientists.

But out of the many different definitions of an *ACID* and a *BASE*,  only 3 of them are generally used in the world of chemistry.

They are as followsπŸ‘‡πŸΌ

πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ
*ARRHENIUS THEORY OF ACID*πŸ‘‡πŸΌ

According to the scientist named *Svant Arrhenius*,

 an  *ACID*  is any substance that can produce *hydrogen ion*(H^+) when it dissolves in water.

Also, according to Arrhenius,

πŸ‘‰πŸΌ a *BASE* is any substance that can produce *hydroxyl ion*(OH^-) when it dissolves in water

As you all know, this definition given to us by Arrhenius, is the popular definitions of acids an bases used majorly at secondary school level.

 *If you take a very careful study of this definition given to us by Arrhenius, you would discover something about it*

You would discover that Arrhenius definitions of both ACIDS and BASES made it compulsory that *water* must be used to confirm if a particular chemical substance is an acid or a base.

*The definition says that the substance will dissolve in water and produce hydrogen ion before it can called an acid and it must dissolve in water to produce hydroxyl ion before it can be called a base*

So you see, according to Arrhenius’ proposal, *water must be present* before a substance can be consider as either an acid or a base.

The question now isπŸ‘‡πŸΌ

*Does it now mean that if water is not available, a substance cannot be considered an acid or base?

 Also,

*Does it mean that, if a compound does not produce hydrogen ion or hydroxyl ion on dissociation, that compound cannot be considered as either an avid or a base?

 Arrhenius definition is good because most acids dissolve in water to produce hydrogen ion and most bases dissolve in water to produce hydroxyl ion.

But there are still acidic substances that do not contain or produce hydrogen ion. *Example is aluminium trichloride (AlCl3)*

The same thing applies to some bases. There are some bases that do not contain or produce hydroxyl ion, *Example is ammonia (NH3)*

Because of this, Arrhenius definition is not 100% correct

Also, *Arrhenius definition shows that without the presence of water, a compound cannot be called an acid or a base*

So, the *limitation or the shortcomings or the problem with Arrhenius theory of acid and base is that he recognized WATER as a necessity to exhibit acidic properties.

Examples of Arrhenius acids areπŸ‘‡πŸΌ

H2SO4

HCl

HNO3

CH3COOH,   etc

See what they produce when they dissolve in solutionπŸ‘‡πŸΌ

H2SO4(aq) —> 2H^+  and  SO4^2-

HCl(aq) —> H^+ and Cl^-

HNO3(aq) —> H^+ and NO3^-

CH3COOH—> H^+ and  CH3COO^-

As you can see, they all produce hydrogen ion (H^+) when they dissolve in solution.

*NOTE*πŸ‘‡πŸΌ

” *(aq)*” means aqueous which means *dissolved in water*

Let us now take a look at *BRONSTED_LOWRY* theory or definition for acid and base.

Please note thatπŸ‘‡πŸΌ

The name *BRONSTED_LOWRY* comprises of two  scientists *BRONSTED* and *LOWRY*.

The two of them have the same definitions for acid and base, so the two names are joined together as one using a hyphen(_) in between the two names like this below.πŸ‘‡πŸΌ

*BRONSTED_LOWRY*

πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ

According to *BRONSTED_LOWRY* theory, πŸ‘‡πŸΌ

An *ACID* is a *proton donor*

While

A *BASE* is a proton acceptor.

Remember that in chemistry, *a proton  simply means a hydrogen ion*(H^+).

According to *BRONSTED_LOWRY*, between two reactants in a chemical reaction, the one that donates it’s proton or hydrogen ion(H^-) is the *ACID* while the one that accepts the proton is the *BASE*.

For instanceπŸ‘‡πŸΌ

*If we have a chemical reactions represented as*πŸ‘‡πŸΌ

πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ

HX   +   Y–  —>  X–   +  HY

where *HX* and *Y*– are the reactants.

πŸ‘‡πŸΌ

If you take a good look at the above reaction between HX and Y–

You would observe that *HX* donated a hydrogen ion (or proton) to *Y*–. After donating the hydrogen ion to *Y*–,
*HX* became *X*–

NOTEπŸ‘‡πŸΌ

*After losing hydrogen ion, X gained one negative charge while after gaining a hydrogen ion, Y lost one negative charge*

[5/16, 12:32 PM] THE CATALYST: πŸ‘‡πŸΌ
[5/16, 12:32 PM] THE CATALYST: In summaryπŸ‘‡πŸΌ

When you remove one hydrogen atom from a substance, you put one negative charge on the remaining substance

But

When you add one hydrogen atom to a substance, you remove one negative charge from the new substance formed.
[5/16, 12:34 PM] THE CATALYST: πŸ‘‡πŸΌ
[5/16, 12:40 PM] THE CATALYST: OK, let us proceed.
[5/16, 12:42 PM] THE CATALYST: *Now, I want you all to observe this reaction below tell me the particular reactant that qualifies to be called BRONSTED_LOWRY acid and the one that qualifies to be called BRONSTED_LOWRY base*

Give reason for your answerπŸ‘‡πŸΌ

*NH3* + *H2O* –> *NH4^+* + *OH–*

(A). NH4^+ is acid while H2O is base

(B). NH3 is acid while H2O is base

(C). H2O is acid and NH3 is base

(D). H2O is base while NH4^+ is acid
[5/16, 12:42 PM] THE CATALYST: πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ
[5/16, 12:53 PM] THE CATALYST: πŸ‘‡πŸΌ
[5/16, 12:53 PM] THE CATALYST: *SOLUTION*…πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ

The correct answer is option *C*

*REASON*..πŸ‘‡πŸΌ

This is because, in the above reaction, H2O donated one of it’s hydrogens to NH3 and became OH– while NH3 accepted the hydrogen and became NH4^+.

According to *BRONSTED_LOWRY* definition, the one that donates hydrogen is the acid while the one that accepts hydrogen is the base…βœ…
[5/16, 1:01 PM] THE CATALYST: πŸ‘‡πŸΌ
[5/16, 1:16 PM] THE CATALYST: *TRY THIS*…πŸ‘‡πŸΌ

observe this reaction below tell me the particular reactant that qualifies to be called BRONSTED_LOWRY acid and the one that qualifies to be called BRONSTED_LOWRY base*

Give reason for your answerπŸ‘‡πŸΌ

*H2O* + *HCl* –> *H3O^+* + *Cl–*

(A). H3O^+ is acid while HCl is base

(B). HCl is acid while H2O is base

(C). H2O is acid and Cl– is the base

(Di H2O is base while Cl– is acid

*SOLUTION*…πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ

The correct answer is option πŸ‘‰πŸΌ *B*

*REASON*..πŸ‘‡πŸΌ

This is because, in the above reaction, HCl donated one of it’s hydrogens to H2O and became Cl– while H2O accepted the hydrogen and became H3O^+.

According to *BRONSTED_LOWRY* definition, the one that donates hydrogen is the acid while the one that accepts hydrogen is the base.

*QUESTION*…πŸ‘‡πŸΌ

In the reaction below, the substance that represents *BRONSTED_LOWRY* base is ___?

*H2O* +  *Cl–* —> *HCl* + *OH–*

(A). Cl–

(B). HCl

(C). H2O

(D). OH–

*SOLUTION*..πŸ‘‡πŸΌ

From the equation given, H2O donated one hydrogen (a proton) to Cl– and became OH–, while Cl– accepted the hydrogen or proton and became HCl.

Therefore, H2O acts as the acid while Cl– acts as the base.

*Answer = A*…βœ…

 *Lewis* definition for acid and  base is somehow  similar to the definition given by *BRONSTED_LOWRY*

According to *LEWIS* theoryπŸ‘‡πŸΌ

An *ACID* is an *electron acceptor.*

 while

A *BASE* is an *electron donor*.

 If you take a critical study at Lewis’ definition of acid and base, you would discover that it is similar to BRONSTED_LOWRY definition.

The difference is that BRONSTED_LOWRY use *proton (hydrogen ion)* while LEWIS uses *electron*

Logically, a proton donor is likely to be an electron acceptor.

*For BRONSTED_LOWRY*, ACID is a *proton donor* while for *LEWIS*, Acid is an *electron acceptor*

This implies that a proton donor is the same as an electron acceptor.

While

A proton acceptor is the same as an electron donor.

According to LEWIS, πŸ‘‡πŸΌ

In a chemical reaction, the substance that accepts a pair of electron is the *ACID* while the substance the donates a pair of electron is the *BASE*

Logically, for a substance to be able to accept a lone pair of electron,

 πŸ‘‰πŸΌ *the substance must have an empty orbital where it can place the electron being accepted because electrons stay at the orbital.

Also, for a substance to donate a pair of electron, πŸ‘‰πŸΌ *the substance must have a lone pair of electron inside it*

NOTE…πŸ‘‡πŸΌ

 *lone pair* electron is a pair (two) of electrons which are not used in chemical bonding during the formation of that substance that carries.

 Logically, for a substance to be able to accept a lone pair of electron, πŸ‘‰πŸΌ *the substance must have an empty orbital*  where it can place the electron being accepted because electrons stay at the orbital.

Also, for a substance to donate a pair of electron, *the substance must have a lone pair of electron inside it*

NOTE…πŸ‘‡πŸΌ

 *lone pair* electron is a pair (two) of electrons which are not used in chemical bonding during the formation of that substance that carries it.

NOTE THISπŸ‘‡πŸΌ

ELECTTOPHILES are the positively charged ions. *Positively charged ions lack electrons because they lost their electrons*. Electrophiles are *electron-loving* substances because they are attracted to electrons since they lack electron, they will accept electrons and they are therefore known as LEWIS ACIDS.

Examples of Lewis acids includesπŸ‘‡πŸΌ

*Cu^Β²+*,  *H^+*,  *Zn^Β²+* etc.

Note that these positively charged ions lost electrons which means that they have an empty orbital in them where the electrons were lost from, so they are Lewis acids.

Some substances that do not have charges(neutral compounds) are also considered as Lewis acids due to the presence of empty orbitals in them.

Examples πŸ‘‡πŸΌ

*AlCl3 and BCl3* etc

*Also*…πŸ‘‡πŸΌ

*NUCLEOPHILES*  are the negatively charged ions. *Negatively charged ions have excess electrons because they gained electrons*.

πŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌπŸ‘‡πŸΌ
 Nucleophiles are *electron-hating* substances because they are not attracted to electrons since they have electrons in excess, they will not accept electrons, rather they will donate electrons to others and they are therefore known as LEWIS BASES.

Examples of Lewis bases includesπŸ‘‡πŸΌ

*OH–*,  *Cl–*,  *Br–* etc.

Some substances that do not have charges(neutral compounds) are also considered as Lewis bases due to the presence of lone pair of electrons in them.

Examples πŸ‘‡πŸΌ

*NH3* and *H2O* etc

 *If you missed any of the topics we have treated here so far, you can click on this*…πŸ‘‡πŸΌ

catalyst44.blogspot.com

*To see the things we have learnt so far*

Always visit

πŸ‘‰πŸΌ catalyst44.blogspot.com

So you can read on your own.

I will be posting note of different topics into the site.

I AM  THE CATALYST…+2348068113736.

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