Question:

Which has highest pH?

Updated On: Jun 23, 2023
  • $CH_{3}COOK$
  • $Na_{2}CO_{3}$
  • $NH_{4}Cl$
  • $NaNO_{3}$
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The Correct Option is B

Solution and Explanation

$pH =\log \frac{1}{\left[ H ^{+}\right]}$ $pH$ is inversely proportional to hydrogen ion concentration. As concentration of $H ^{+}$decreases pH increases and vice versa. (a) Ammonium chloride $\left( NH _{4} Cl \right)$ is a salt of weak base and strong acid. So, its aqueous solution will be acidic as $NH _{4} Cl + H _{2} O \longrightarrow \underset{\text{weakbase}}{NH _{4} OH} + \underset{\text{strong acid}}{HCl}$ So, $pH$ of $NH _{4} Cl$ is less than 7 (b) $NaNO _{3}$ (Sodium nitrate) is the salt of strong acid and strong base. So, its aqueous solution is neutral as $NaNO _{3}+ H _{2} O \longrightarrow \underset{\text { strong base }}{NaOH} +\underset{\text { strong acid }}{ NNO _{3}}$ So, $pH$ of $NaNO _{3}$ is 7 . (c) $CH _{3} COOK$ (Potassium acetate) is a salt of strong base and weak acid. Its aqueous solution will be basic and $pH$ value will be $>7 \approx 8.8$ $CH _{3} COOK + H _{2} O \longrightarrow \underset{\text { weak acid }}{ CH _{3} COOH }+\underset{\text { strong base }}{ KOH }$ (d) $Na _{2} CO _{3}$ (Sodium carbonate) is a salt of strong base and weak acid. Its aqueous solution is also basic and its $pH$ value will be more than 10. $Na_2CO_3 + H_2O \longrightarrow \underset{\text{strong base}}{2NaOH} + \underset{\text{weak acid}}{H_2CO_3}$
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Concepts Used:

Equilibrium

An equilibrium represents a state in a process when the observable properties such as color, temperature, pressure, concentration etc do not show any change.

The word equilibrium means ‘balance’ which indicates that a chemical reaction represents a balance between the reactants and products taking part in the reaction. The equilibrium state is also noticed in certain physical processes such as the melting point of ice at 0℃, both ice and water are present at equilibrium.

In the case of physical processes such as the melting of solid, dissolution of salt in water etc., the equilibrium is called physical equilibrium while the equilibrium associated with chemical reaction is known as chemical equilibrium.

Equilibrium in Chemical changes

The chemical equilibrium in a reversible reaction is the state at which both forward and backward reactions occur at the same speed.

The stage of the reversible reaction at which the concentration of the reactants and products do not change with time is called the equilibrium state.

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Types of Chemical Equilibrium

There are two types of chemical equilibrium:

  • Homogeneous Equilibrium
  • Heterogeneous Equilibrium

Homogenous Chemical Equilibrium

In this type, the reactants and the products of chemical equilibrium are all in the same phase. Homogenous equilibrium can be further divided into two types: Reactions in which the number of molecules of the products is equal to the number of molecules of the reactants. For example,

  • H2 (g) + I2 (g) ⇌ 2HI (g)
  • N2 (g) + O2 (g) ⇌ 2NO (g)

Reactions in which the number of molecules of the products is not equal to the total number of reactant molecules. For example,

  • 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
  • COCl2 (g) ⇌ CO (g) + Cl2 (g)

Heterogeneous Chemical Equilibrium

In this type, the reactants and the products of chemical equilibrium are present in different phases. A few examples of heterogeneous equilibrium are listed below.

  • CO2 (g) + C (s) ⇌ 2CO (g) 
  • CaCO3 (s) ⇌ CaO (s) + CO2 (g)

Thus, the different types of chemical equilibrium are based on the phase of the reactants and products.

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