Experimental Results
Using an Analytical Balance to Prepare 100.0 mL of a 5.0 mmol/L Glucose Stock Solution
Enter the exact mass of glucose (to 3 decimal places) that you weighed during Practical 2 to prepare the 5.0 mmol/L glucose stock solution into Table 1.
Table 1: Exact mass of glucose weighed to prepare the 5.0 mmol/L glucose stock solution.
Exact mass of glucose = 0.090 grams (to 3 decimal places)
Using the mass (grams) of glucose that you provided in Table 1, calculate the concentration of glucose in the stock solution as mmol/L. You must show your full working in the space below to gain full marks for this question.
Calibration of an Automatic Pipetter
Enter your experimental data for the calibration of two different automatic pipetters into Table 2. The first was calibrated at 1.000 mL (1000 mL) and the second at 0.200 mL (200 mL).
Also provide in Table 2 the relative error (%) and relative precision (%) for the calibration of the two automatic pipetters. The full working of the relative error (accuracy) and relative precision for both volumes delivered and reported in Table 2 must be shown on the next page in the spaces provided.
Table 2: Summary of your experimental data for the calibration of two automatic pipetters set at 1.000 mL and 0.200 mL.
Temperature of water: 21 oC
Density of water: ................ g/mL
Measurement of 1.000 mL (1000 mL)
Mass of water delivered: 0.995 g 0.994 g 0.994 g
Volume of water delivered: ............ mL ........... mL ........... mL
Average volume (Vave): ................... mL
Measurement of 0.200 mL (200 mL)
Mass of water delivered: 0.199 g 0.199 g 0.198 g
Volume of water delivered: ........... mL ........... mL ........... mL
Average volume (Vave): ................... mL
Preparation of a Glucose Standard
Enter your duplicate absorbance values into Table 3 for your 0.5 mmol/L glucose standard solution and the standard prepared by the technical staff. For your own standard solution, select your best duplicate absorbances for entry into Table 3.
Table 3: Absorbance values for the glucose standard solutions at 405 nm.
|
Glucose standard solutions
|
Duplicate 1
Absorbance
|
Duplicate 2
Absorbance
|
Mean
Absorbance
|
|
Your 0.5 mmol/L glucose standard
|
1.152
|
1.189
|
|
|
Technician’s 0.5 mmol/ glucose standard
|
1.143
|
1.143
|
|
Calculate the percentage (%) difference between your 0.5 mmol/L glucose standard and the technician’s 0.5 mmol/L glucose standard using the mean absorbance values. Show your full working below and round your answer to 1 decimal place.
Percentage (%) difference = | Your mean abs - Technician’s mean abs | x 100
Technician’s mean abs
General Question
Describe three (3) potential errors that could occur when testing the accuracy and precision of an automatic pipettor using an analytical balance. Your answers must be full sentences.
