Answer :
To calculate the pH of the solution when the given substances are added together, we need to consider the acid-base reactions that occur.
1. 20 mL of 0.001 M HCl and 40 mL of 1.5 M Acetic acid:
Since acetic acid is a weak acid, it partially ionizes in water:
CH3COOH ⇌ CH3COO- + H+
HCl, on the other hand, is a strong acid and completely ionizes:
HCl → H+ + Cl-
Since HCl is a strong acid, it will completely dissociate, while acetic acid will only partially dissociate. The excess of H+ ions from HCl will effectively shift the equilibrium of the acetic acid towards the CH3COOH ⇌ CH3COO- + H+ reaction.
This will result in an increase in the concentration of acetate ions (CH3COO-) and H+ ions.
2. 20 mL of 0.001 M HCl and 50 mL of 2.5 M Sodium Acetate:
Sodium acetate dissociates in water:
CH3COONa → CH3COO- + Na+
Similar to the previous case, the addition of HCl will lead to an increase in the concentration of H+ ions due to the complete dissociation of HCl.
The excess H+ ions will shift the equilibrium of the sodium acetate towards the CH3COONa ⇌ CH3COO- + Na+ reaction, resulting in an increase in the concentration of acetate ions (CH3COO-) and H+ ions.
In both cases, the presence of the acetate ions will act as a buffer, helping to resist changes in pH by absorbing excess H+ ions.
To calculate the pH precisely, the equilibrium calculations would need to be performed.
However, since the initial concentrations of HCl and acetate ions are relatively low, and the volumes are mixed in a 1:2 ratio (20 mL : 40 mL or 20 mL : 50 mL), the resulting pH is expected to be slightly acidic but close to neutral.
To know more about acid-base reactions refer here
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