posted by Kim on .
You weigh a sample of a monoprotic unknown acid and dissolve it in 50.00 mL of distilled water. Exactly half of this solution is titrated with Sodium Hydroxide to the phenolphthalein end point.
The pH of the other half of the original solution is measured with a pH meter. The "neutralized" solution is added to the "original" solution and the pH of this combined "final" solution is also measured.
The following are the measured values:
Mass of unknown acid 1.2357 g
Volume of NaOH used in titration 16.04 mL
Concentration of the NaOH used 0.2098 M
pH of the original acid solution 2.02
pH of the final acid solution 3.29
CALCULATE the following
(a) Molecular Weight of Acid used in titration ___________________
(b) Molarity of UNKNOWN Acid solution from titration ___________________
(c) Ka of UNKNOWN Acid ___________________
(d) Concentration of undissociated Acid from pH measurements ___________________
(e) Total concentration of UNKNOWN acid from pH measurements ___________________
For each trial, enter the amount of heat lost by the calorimeter, qcalorimeter.
Be careful of the algebraic sign here and remember that the change in temperature is equal to the final temperature minus the initial temperature.
Report your answer using 4 digits. Note, this is 1 or 2 digits beyond the correct number of significant figures.
Trial # Initial Masswater Tiwater Tf qwater qcalorimeter
#1: 86.281 51.2 23.7 -9927.
#2: 87.777 49.0 29.0 -7345.
#3: 89.997 52.2 27.2 -9413.