A solution of acetic acid having a concentration of about 0.2M is to be titrated using 0.200M NaOH. Select an indicator for the titration.
what salt will the solution contain at the equivalence point?
what is the approximate concentration of this salt at the equivalence point?
will the solution of this salt be acidic or basic?
what is the approximate pH of this solution?
which indicator will have a pKa closest to the pH of the salt solution?
I shall be happy to review your thoughts. Too many questions per post and not enough input from you. Surely you know parts of this. What part do you not understand?
To select an indicator for the titration, you will need to consider the pH range of the equivalence point and choose an indicator that changes color within that range. In this case, since acetic acid (CH3COOH) is being titrated with NaOH, which is a strong base, the equivalence point will occur when all the acetic acid has reacted with the NaOH. At this point, the solution will contain the salt sodium acetate (CH3COONa).
To determine the approximate concentration of this salt at the equivalence point, you can use stoichiometry. The balanced equation for the reaction between acetic acid and sodium hydroxide is:
CH3COOH + NaOH -> CH3COONa + H2O
This shows that one mole of acetic acid reacts with one mole of sodium hydroxide to produce one mole of sodium acetate. Since the initial concentration of the acetic acid is 0.2M, and assuming complete reaction, the concentration of sodium acetate at the equivalence point will also be 0.2M.
The solution of sodium acetate will be basic. Sodium acetate is the conjugate base of acetic acid, meaning it can accept a proton (H+) from water, making the solution basic.
To approximate the pH of the sodium acetate solution, you can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, sodium acetate (CH3COONa) is the salt of the weak acid, acetic acid (CH3COOH), so the pKa of acetic acid can be used. The pKa of acetic acid is approximately 4.76. At the equivalence point, the concentration of both the acetic acid and its conjugate base (sodium acetate) are 0.2M. Plugging these values into the Henderson-Hasselbalch equation will give you the approximate pH of the solution.
To choose an indicator with a pKa closest to the pH of the salt solution, you should look for an indicator that has a pKa value close to 4.76, the approximate pH of the sodium acetate solution. One such indicator is phenolphthalein, which has a pKa of around 9.2. Phenolphthalein can be used since its transition range (color change) occurs within the pH range of the equivalence point.