Consider the following aqueous chemical equilibrium of benzoic acid, a weak acid

Question

Consider the following aqueous chemical equilibrium of benzoic acid, a weak acid:

C6H5COOH (aq) + H2O(l) = H3O+(aq) + C6H5COO-(aq)

1. Addition of H3O+ to the chemical equilibrium( increases or decreases?) ______ the amount (moles) of the C6H5COO- in the system

2. Addition of OH- to the chemical equilibrium _________ the amount (moles) of C6H5COOH in the system

3. Removal of C6H5COO- from the chemical equilibrium __________ the amount of H3O+ in the system

4. Increasing the pH of the solution from the chemical equilibrium ___________ the amount of C6H5COOH in the system

Explanation / Answer

These questions can be solved on the basis of le Chatelier's principle that says , the system at equillibrium always tries to cancel out or nullify the effect of external factor on itself , by shifting towards forward or backward direction .

Ans 1. Addition of H3O+ which is a product , will shift the equillibrium backwards that tends to make reactants , hence the amount of the C6H5COO- in the system decreases .

Ans 2. Addition of OH- to the system , will cause an increase in the number of moles of water as it reacts with hydronium ion to give water , hence the equillibrium shifts towards right , and the amount of C6H5COOH decreases.

Ans 3. C6H5COO- is the product in the following reaction equillibrium , removing it will cause the equillibrium to shift to right , hence the amount of H3O+ in the system increases .

Ans 4. pH of the solution increases as the acid is diluted , due to which the weak acids dissociate more , hence benzoic acid dissociates more so the amount of C6H5COOH decreases in the system.

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