Consider the steps you calculated the mass % concentration of vinegar and ration
ID: 579648 • Letter: C
Question
Consider the steps you calculated the mass % concentration of vinegar and rationalize how will the following affect the calculated mass % concentration: a. Measured out 11 ml. vinegar sample each time instead of 10 mL b. Before titration, rinsed the buret with DI water only without using NaOH solution; c. Some NaOH solution remain on the wall of flask and never reach the reaction mixture. 4. 5. A quality control chemist at Dow Chemical tried to determine purity of NaOH using titration. He measured out 0.500 g NaOH sample, and dissolved it in 20 ml. water. 22.5 ml. of a 0.500 mol/L. HC solution was used to reach the end point. Assume the impurity did not react with HCl, what is the mass of desired compound mass of whole sample % Purity = × 10096 %purity of this NaOH sample?Explanation / Answer
4a) The mass% concentration of vinegar is obtained by determining the mass of acetic acid in vinegar by titration with NaOH. The mass% concentration is given as
mass% concentration = (mass of acetic acid)/(volume of vinegar)*100
We were supposed to use 10 mL of vinegar solution; however, we used 11 mL for all the trials. The mass of acetic acid was determined from the titration and is therefore, constant. However, since the denominator in the expression is higher than desired, the calculated mass% concentration of acetic acid will be lower.
b) The neutralization reaction between acetic acid (in vinegar) and NaOH is given as
CH3COOH (aq) + NaOH (aq) --------> CH3COONa (aq) + H2O (l)
The burette must be rinsed with NaOH solution to ensure that no water remains in the burette during titration. Water dilutes NaOH and the concentration of NaOH will therefore, change. Infact, the NaOH gets dilute and the given sample of vinegar will require a higher volume of NaOH to reach the equivalence point. However, the mass% concentration of acetic acid in vinegar will remain unchanged.
In order that the concentration of the supplied NaOH doesn’t fall off, the burette must be rinsed thoroughly with NaOH before beginning the titration.
c) The neutralization reaction is provided above. If some NaOH remained in the flask, acetic acid will not be completely neutralized and the calculated mass of acetic acid neutralized will be lower than the actual amount present. Hence, the calculated mass and thus the mass% concentration of acetic acid in vinegar will be lower than the actual values.