Answer to Question #93583 in General Chemistry for Susan cruz

Question

1. A 20 mL volume of previously boiled, deionized water is added to the Erlenmeyer flask to prepare the sample of titration. Explain why this volume is not critical to the analysis.

2. Previously boiled, deionized water is unavailable. In a hurry to pursue the analysis, deionized water ( not boiled ) is added. How does this attempt to expedite the analysis affect the reported percent acetic acid; too high, too low, or unaffected? Explain.

3. The mL of water added to the Erlenmeyer flask is to be previously boiled, deionized water. Since water does absorb the CO2 from the atmosphere and since CO2 dissolved 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

1. The volume of water is umimportant because it doesn't affect the number balance of hydronium and hydroxide ions. It is there just to make the endpoint reading easier.

2. The percent by mass of acetic acid will be too low because of the acid that may still be in the water.

3. The amount of acetic acid in vinegar is determined by the volumetric titration of acetic acid with standardized NaOH solution. When atmospheric carbon dioxide is absorbed by deionized water used in the titration, it would react with water and form carbonic acid. 

When the deionized water is contaminated with carbonic acid, it would result in the consumption of a higher amount of NaOH for neutralization. Therefore, the amount of acetic acid determined would be too high than it should be.