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Ionic Product of Water for IIT JEE

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Last updated date: 21st May 2024
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Ionic Product of Water - Examples with Solutions

Water is the very essential molecule for the normal functioning of the body in all living organisms. Water in a pure form is made up of two molecules of hydrogen and one molecule of oxygen, which in the molecular formula is denoted as H2O. Pure water possesses a very weak electrolyte property which can easily undergo the Self ionization process and spit into two molecular ion parts.

  1. Hydrogen ion (H+)

  2. Hydroxide ion (OH-)


The product of concentrated H+ and OH- ions in the water at a certain temperature is termed as an ionic product of water. Ions vary with the temperature. 


The process where water undergoes self-ionization is also known as Autoprotolysis. The equation of the autoprotolysis (self-ionization) is shown as:


H2O OH- + H+


The hydrogen ion formed from the ionization of pure water is highly reactive in nature which further reacts with the other molecules of pure water and forms hydronium ion (H3O+)


H2O + H+ H3O+


The Law of mass action for the self-ionization reaction of pure water at chemical equilibrium, the value of the dissociation constant K is the relationship between the concentration of reactants and product, for this ionization of pure water reaction; equation of dissociation constant K written as:


\[K=[H+][OH-]/[H_{2}O]\]


Or   


\[[H^{+}][oH^{-}]=k[H_{2}o]\]


Here the dissociation of the pure water occurs to a very small extent; hence the concentration of undissociated water molecules, \[[H_{2}O]\], is considered as constant. Thus, the product \[[H_{2}O]\] gives another constant which is denoted as Kw and the equation of Kw is shown as:


\[[H^{+}][oH^{-}]=kw\]


Here, the constant (Kw), is termed as an ionic product of water.


During the self-ionization process, the pure water can dissociate the water molecule to form one hydroxyl OH- ion (which is alkaline in nature) and one hydroxide H+ ion (which is acidic in nature), hence the autoprotolysis of pure water can act both as an acid as well as a base. 


Water can be converted to the acidic state by such components/ substances which increase the concentration of Hydrogen (H+) ions or decrease the concentration of Hydroxide ion (OH-) ions. In the same way, water can also be converted to the basis by such components/ substances which increase the concentration of Hydroxide ion (OH-) or decrease the concentration of Hydrogen (H+) ions.


In pure water, the concentration of the hydrogen H+ ion (hydronium H3O+ ion) is always equivalent to the concentration of the hydroxide OH- ion. In simple terminology, it is also stated that the generation of every single hydrogen H+ ion (hydronium H3O+ ion) equivalent ratio of hydroxide OH- ion is also generated as well. This statement also states reversely as the number of generated hydroxide OH- ions is equal with the number of generated hydrogen H+ions (hydronium H3O+ ions).


Effect of Temperature on KW

Concentrations of H+ and OH- ions in the pure water of a product at a specific temperature is normally known as an ionic product of water. The value of Kw (ionic product of water) rises with the rise of temperature, i.e., the concentration of H+ and OH- ions rises with temperature rises. Some constant values of KW at different temperatures are shown in below table:


Temperature (°C)

Value of Kw

0

0.11 x 10-14

10

0.31 x 10-14

25

1.00 x 10-14

100

7.50 x 10-14


At 25°C temperature, the value of KW of pure water is 1 x 10-14. Although pure water is neutral in nature, hence the concentration of the H+ ion and OH- ion must be equal.


So, [H+] = OH˜


 = X


Put the value of [H+] and OH˜


into the KW equation


\[[H^{+}][oH^{-}]\]=KW= 1 x 10-14(at 25°C temperature)


\[[H^{+}][oH^{-}]\]=X2= 1 x 10-14


Hence, X = 1 x 10-7 M


So from the equation value of


\[[OH^{-}]=[H^{+}]\]= X = 1 x 10-7 M


which is also written as\[[OH^{-}]=[H^{+}]\]= 1 × 10-7 mol litre-1


This interprets that at 25°C temperature; in 1 litre solution of pure water only 10-7 moles of water is present in the ionic form out of total moles of pure water (i.e. approximately 55.5 moles).


When the addition of an acid or the base happens in the pure water, then the concentration of the ionic product concentration of the pure water can be calculated by using the ionic product constant equation \[[H^{+}][oH^{-}]=kw\], where the value of KW is constant at specific temperature but the concentration of the H+ and OH- ions do not remain the same. 


The addition of the acid leads to the rise in the concentration of the hydrogen H+ ion or hydronium H3O+ ion or in other terms we can say that it leads to a decrease in the concentration of the hydroxyl OH- ion.


i.e. \[[H^{+}] or [H_{3}O^{+}] > [OH^{-}]\]; (Acidic solution)


Similarly, the addition of the base leads to the rise in the concentration of the hydroxyl OH- ion or in other terminology it decreases the concentration of the hydrogen H+ion or hydronium H3O+ ion


i.e. \[[OH^{-}] > [H^{+}]\]; (Alkaline or basic solution)


The Concentration of Ions in Neutral Acidic and Basic Condition

In a Neutral solution, the concentration of the H+ ion and OH- ion are equivalent to each other hence the value of the hydrogen ion and hydroxyl ion are the same.  


\[[H^{+}] = [OH^{-}]\] = 1 x 10-7 M


But in an Acidic solution, the concentration of H+ ion is higher than the concentration of the OH- ion, hence the value of the H+ ion is always greater than the value of OH- ion. This shows that the concentration of H+ ion is always higher than the 1 x 10-7 M and similarly the concentration of OH- ion is always lesser than the 1 x 10-7 M as shown below:


\[[H^{+}] > [OH^{-}]\]


Where, \[[H^{+}]\] > 1 x 10-7 M


Or, \[[OH^{-}]\] < 1 x 10-7 M


In Alkaline (basic) solution, the concentration of OH- ion is higher than the concentration of the H+ ion, hence the value of the OH- ion is always greater than the value of H+ ion. That shows that the concentration of OH- ion is always higher than the 1 x 10-7 M and similarly the concentration of H+ ion is always lesser than the 1 x 10-7 M as shown below:     


\[[OH^{-}] > [H^{+}]\]


Where, \[[OH^{-}]\]> 1 × 10-7 M


Or, \[[H^{+}]\] < 1 x 10-7 M


Hence, the value shows that the solution of pure water must be acidic in nature if the concentration of the hydrogen H+ ion is higher than 1 x 10-7 M and alkaline or basic in nature if the concentration of the H+ ion is lesser than 1 x 10-7 M.


The table shows the type of nature exhibited by water due to the amount of H+ ion concentration it consumes:


Concentration of [H+] ion

Nature of Water

10-0,10-1,10-2,10-3,10-4,10-5,10-6

Acidic

10-7

Neutral

10-14,10-13,10-12,10-11,10-10,10-9,10-8

Alkaline


Similarly, the value shows that the solution of pure water must be basic in nature if the concentration of the hydroxyl OH- ion is higher than 1 x 10-7 M and alkaline or basic in nature if the concentration of the OH- ion is lesser than 1 x 10-7 M.


The table shows the type of nature exhibited by water due to the amount of OH- ion concentration it consumes:


Concentration of [OH-] ion

Nature of Water

10-14,10-13,10-12,10-11,10-10,10-9,10-8

Acidic

10-7

Neutral

10-0,10-1,10-2,10-3,10-4,10-5,10-6

Alkaline


It is concluded that each aqueous solution whether it is acidic, basic or neutral possesses both hydrogen H+ ion and hydroxyl OH- ion that are present in the same or different proportions. But the ionic product concentration KW of the water always remains constant 1 × 10-14 at a temperature of 25°C. Hence, when the concentration of one ion increases, accordingly the concentration of the other ion is decreased but the overall concentration of the product remains constant.


Importance of the Ionic Product of Water  

The ionic product of water is very important in knowing the balance of Acid and Base and in calculating the disorder of acid-base.


Human plasma is a solution that is Aqueous in nature and has to run by chemical rules known as electrical neutrality and ionic product constancy of water. 


In water, some molecules form hydronium ion (H3O+) which is also known as hydronium, with Hydroxide ion (OH-) by accepting a second water molecule. When this happens, both the ions react together to make water once again. 


The electroneutrality principle clearly states that plasma should be neutral electrically and the total sum of anions must match the sum of cations. The ionic product of water should be constant. Hence, the concentration of plasma of hydrogen ions totally depends on the concentration of ionic plasma. 


When Plasma anions become out of proportion of cations, their accumulation induces electrical imbalance with a fall of hydroxide ions that causes a rise in hydrogen ions. To protect the plasma pH from serious deviations, the concentration of plasma bicarbonate should be adjusted to these changes. 

 

Characteristics of Ions After Dissolved in Water

Ionic compounds when dissolved in water, break apart through a process into the ions. When in water, the ions attract to the molecules of water, a polar charge within each of them. If the force between water molecules and the ions gets strong enough and breaks the bond between these ions, makes the compound dissolve. The ions separate in the solution, each surrounded by the water molecules to prevent them from reattaching. The ionic solution then becomes an electrolyte, which means that it can conduct electricity. 


Covalent compounds

Covalent compounds when dissolved in water, break into molecules, not individual atoms. Water as we know is a polar solvent but covalent compounds are mostly nonpolar. Covalent compounds don't always dissolve in water, making a different layer on the surface of the water. 

FAQs on Ionic Product of Water for IIT JEE

1. If the concentration of the \[[H^{+}]\] ion is 10-2 M then what is the concentration of  \[[OH^{-}]\] ion and what is the nature of the aqueous solution?

Overall concentration of aqueous product (KW) = 10-14 M. 


Concentration of \[[H^{+}]\] ion = 10-2 M


Now, by applying the equation of ionic product of aqueous solution, KW = \[[H^{+}][oH^{-}]\]


If the value of \[[H^{+}]\] = 10-2 M and value of KW = 10-14 M, by putting the value into the equation


KW= 10-14M= 10-2 M x \[[OH^{-}]\]


Hence, the obtained value of \[[OH^{-}]\]ion from the equation is = 10-12 M;


Here this aqueous product consumes 10-2 M concentration of hydrogen \[[H^{+}]\] ion and 10-12 M hydroxyl \[[OH^{-}]\] ion; that concludes the aqueous solution is acidic in nature.

2. If the concentration of the \[[H^{+}]\] ion is 10-10 M, then what is the concentration of [OH-] ion and what is the nature of the aqueous solution?

The concentration of \[[H^{+}]\] ion = 10-10 M and concentration aqueous product = 10-14 M.


By applying KW = \[[H^{+}][oH^{-}]\]; the obtained concentration of \[[OH^{-}]\] ion = 10-4 M.


Here this aqueous product consumes 10-10 M concentration of hydrogen \[[H^{+}]\] ion and 10-4 M hydroxyl \[[OH^{-}]\] ion, which concludes the aqueous solution is basic in nature.

3. What are Cations and Anions?

To understand the vast concept of cations and anions, we should first learn about ions. An atom that is electronically charged or a group of atoms that are electronically charged, termed as ions. There are two types of ions, Cations and Anions. They are both charged electronically but the only difference between them is one is positively charged and the other one is negatively charged. The one with the negative charge is Anion and the one with the positive charge is Cation. To learn better, look at the study material provided by Vedantu online.

4. Discuss Electrons, Protons and Neutrons.

The matter of particles has a basic property known as Electric Charge. These electrical charges are found in Electrons, Protons and Neutrons. The one with the negative charge is Electron. The one with the positive charge is Proton and the one with no charge is Neutron. In a normal atom, there is no charge available. This means that the total number of Electrons match the total number of Protons. If an atom gains electrons, it becomes negatively charged. When it loses electrons, it becomes positively charged.

5. Describe in your words the solubility product?

The solubility product is the equilibrium of a chemical reaction where an ionic compound of solid dissolves to create its own ions in the solution. This term is used only for the solutions which are saturated. If the substance of the solubility product is smaller, the solubility of that substance will be lower as well. The reason is that the solubility product defines the number of dissolved ionic species which are present in the solution. If the ionic species shows a little amount, it means that the substance is not dissolved efficiently in the solvent.