Question

The 20mL of water added to the Erlenmeyer flask is to be previously boiled, deionized water. Since water does absorb CO₂ from the atmosphere and since CO₂dissolved in water causes it to be slightly acidic, will the use of deionized water that has not been previously boiled cause the mass of acetic acid in the vinegar to be calculated as too high or too low. Explain.

Answer 1

Using deionized water that has not been boiled can lead to an overestimation of acetic acid mass in vinegar because unboiled water can absorb atmospheric CO2, slightly acidifying the water and potentially affecting the ionization equilibrium.

Step-by-step explanation:

Using deionized water that has not been previously boiled in the determination of the mass of acetic acid in vinegar may cause the calculated mass to be too high. This is because deionized water, though free from ions, still absorbs CO2 from the atmosphere. When dissolved CO2 reacts with water, it forms carbonic acid, resulting in a slightly acidic solution which can contribute additional ionized acid to the solution.

The reaction of acetic acid in water can be represented as:

CH3COOH(aq) + H2O(l) ⇌ H3O+(aq) + CH3COO−(aq)

Only a small fraction of acetic acid is ionized in the water. However, if the solution contains additional H3O+ formed from the dissolved CO2, that could shift the equilibrium position, resulting in more acetic acid ionizing to re-establish equilibrium. For accurate results, boiling the water prior to use helps to drive off dissolved CO2, reducing the chance of overestimating the concentration of acetic acid in the vinegar.