Weak Acid/Base Equilibria: C6H5OH & C6H5NH2 K_a & K_b

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In summary, C_6H_5OH is a weak acid and C_6H_5NH_2 is a weak base when dissolved in water. The equilibrium expressions for K_a and K_b involve the concentrations of the conjugate base/acid and the new acid/base, divided by the initial concentration of base/acid. The concentration of water, which is constant, is cancelled out of the equation. Ka and Kb are equilibrium constants for the reactions, and can be calculated using chemical calculators such as BATE and CASC. The second dissociation steps can be disregarded in this calculation.
  • #1
APool555
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C_6H_5OH acts as a weak acid and C_6H_5NH_2 acts as a weak base in water. Write equalibrium expressions for K_a and K_b.
 
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  • #2
Hi my friend. What you should do here is write first the equilibrium reaction for these two substances ionisation in water, then deduce an expression for Kc-eqm constant. This expression will include the concentration of water, which is constant and thus cancels out of the equation. Then replace Kc by simply Ka or Kb, a new sort of equilibrium constant for these reactions. What you shoulb find is the Ka/Kb is simply the product of the concentrations of the conjugate base/acid and the new acid/base divided by the initial concentration of base/acid. Yours, Joe
 
  • #4
First, show your work, if you had read the text you should at least know how to start.
 

Related to Weak Acid/Base Equilibria: C6H5OH & C6H5NH2 K_a & K_b

1. What is the difference between a weak acid and a strong acid?

A weak acid is an acid that does not completely dissociate in water, meaning that only a small fraction of the molecules break apart into ions. A strong acid, on the other hand, is an acid that completely dissociates in water, producing a high concentration of hydrogen ions.

2. Can you provide an example of a weak acid?

One example of a weak acid is acetic acid (CH3COOH). It is commonly found in vinegar and only partially dissociates in water, producing both hydrogen ions and acetate ions.

3. How do you calculate the acid dissociation constant (Ka) for a weak acid?

The acid dissociation constant (Ka) is equal to the concentration of the products (H+ and conjugate base) divided by the concentration of the reactant (weak acid). This can be represented by the equation Ka = [H+][A-]/[HA].

4. What is the relationship between Ka and the strength of a weak acid?

The acid dissociation constant (Ka) is a measure of the strength of a weak acid. A higher Ka value indicates a stronger acid, meaning that more hydrogen ions will be produced in water.

5. How does temperature affect the equilibrium constant for a weak acid?

The equilibrium constant (Ka) for a weak acid is temperature-dependent. An increase in temperature will shift the equilibrium to the left, decreasing the concentration of hydrogen ions and lowering the Ka value. A decrease in temperature will shift the equilibrium to the right, increasing the concentration of hydrogen ions and increasing the Ka value.

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