Buret was rinsed with water and NaOH, and followed by filling with NaOH solution made in the first week of lab. An acid of unknown concentration was prepared by the instructor and given for analysis. 25.00 mL of the acid was transferred into an Erlenmeyer flask using a volumetric pipette and 2-3 drops of phenolphthalein were added. The resulting solution was titrated with NaOH to achieve the faint pink endpoint and [unknown] was calculated according to the volume of NaOH used.
The purpose of this experiment was to determine the [unknown acid] by titrating it with a standardized NaOH solution using phenolphthalein as the indicator. NaOH and the unknown acid HA react as shown in reaction below to form sodium salt and water:
NaOH (aq)+HA(aq)→NaA(aq)+H_2 …show more content…
Therefore, the true concentration of the unknown acid is expected to lie between 0.1064 – 0.1068 M, if the titrations are performed infinite number of times. Out of the three trials, as shown in table 1, trial 1 and 2 both resulted in [unknown] of 0.1067 M reflecting on the precision and accuracy of the titrations. Trial 3 resulted in [unknown] of 0.1065 M, which skewed the average. Determinate error made while pipetting the acid might have resulted in transfer of more acid than 25.00 mL, thus the calculated concentration was smaller compared to other trials. Even though the average is skewed by the third trial, the relative standard deviation is (RSD) is only 0.09% implying that the data is reproducible. Propagated uncertainty in the [unknown acid] was calculated as 0.0004 M for all the three trials. Among the parameters, volume in NaOH dispensed recorded the highest uncertainty of ±0.07 mL. As the volume is an important factor in calculating the [unknown acid], if methods are employed to reduce the error in the volume, quality of the result will increase. Even though not calculated, the visual detection of the endpoint is also a major source of error. This is a random error and cannot be avoided, but lighter the color, more accurate the
The purpose of this experiment was to determine the [unknown acid] by titrating it with a standardized NaOH solution using phenolphthalein as the indicator. NaOH and the unknown acid HA react as shown in reaction below to form sodium salt and water:
NaOH (aq)+HA(aq)→NaA(aq)+H_2 …show more content…
Therefore, the true concentration of the unknown acid is expected to lie between 0.1064 – 0.1068 M, if the titrations are performed infinite number of times. Out of the three trials, as shown in table 1, trial 1 and 2 both resulted in [unknown] of 0.1067 M reflecting on the precision and accuracy of the titrations. Trial 3 resulted in [unknown] of 0.1065 M, which skewed the average. Determinate error made while pipetting the acid might have resulted in transfer of more acid than 25.00 mL, thus the calculated concentration was smaller compared to other trials. Even though the average is skewed by the third trial, the relative standard deviation is (RSD) is only 0.09% implying that the data is reproducible. Propagated uncertainty in the [unknown acid] was calculated as 0.0004 M for all the three trials. Among the parameters, volume in NaOH dispensed recorded the highest uncertainty of ±0.07 mL. As the volume is an important factor in calculating the [unknown acid], if methods are employed to reduce the error in the volume, quality of the result will increase. Even though not calculated, the visual detection of the endpoint is also a major source of error. This is a random error and cannot be avoided, but lighter the color, more accurate the