The objective of this experiment is to;
•Identifying the range and limits of a measuring apparatus.
•Rectifying any instrumental error that might be present in an instrument.
•Investigating the limits and capabilities of a measuring instrument.
•Determining the accuracy of the actual volume of a volumetric pipette, volumetric flask & measuring cylinder.
The purpose of this experiment is to investigate the measurement of the actual volume contents of volumetric glassware. If there is a slight variation in this instrument, it would cause systematic error and thus, the accuracy of results of an experiment or investigation would be affected.
All volumetric glassware has marking on it. It is either being marked with TD or TC, which brings the meaning of ‘to deliver’ and ‘to contain’ respectively. For example, a pipette has a marking of TD, which means a pipette is marked as a ‘to deliver’. Whereas, volumetric flask has TC as its marking, meaning it is marked as a ‘to contain’.
A volumetric pipette & measuring cylinder can be calibrated by just weighing the water they deliver. As for volumetric flask, the weight of an empty flask is recorded. Next, weigh the flask after filling it with water to the mark.
After that, it is crucial to convert the mass to volume. The water density at a temperature will aid this process. The compliance of the Volume Occupied by 1.000g of Water Weigh in Air table is deemed necessary throughout the comparison.
In order to obtain the true volume of volumetric glassware holds, this formula will be used.
This experiment shall be repeated twice more to enhance accuracy of the results obtained. Besides detecting systematic errors, this experiment would aid on the technique and understandings to the correct use of these equipments.
•10ml volumetric pipette
•25ml volumetric pipette
•100ml volumetric flask
•Small conical flask
1)Volumetric pipette calibration (10ml & 25ml)
Transfer pipettes are being cleaned if necessary. The necessity of cleaning is judged by observing the water if it does not drain uniformly and water droplet is seen in the inner surface. To perform the cleaning of this instrument, use a cleaning solution or detergent.
The temperature of deionised water used to calibrate these pipettes must be at room temperature. The water temperature is then recorded uniformly. By using an analytical balance or a top loading balance, the water is weigh to its nearest ml by using a container. A container, either a small conical flask or a weighing bottle is used.
- An empty weighing bottle must be weighed to its nearest mg. - Fill the pipettes with deionised water to the mark.
- Water contained in the pipettes is then transferred to the weighing bottle. In order to prevent evaporation from occurring is advised to cap the bottles.
- To obtain the water mass delivered from the pipette, the weighing bottle must be re-weighed.
- Convert the results to volume by using the mass volume conversion table.
Repeat these procedures twice more on all pipettes.
2.Volumetric flask calibration (100ml)
Dry the flask if necessary. To perform this action, the flask is clamped inverted. Take note that this procedure must be done only at room temperature.
The deionised water is used to fill the flask up to the mark. Next, the flask is re-weighed.
Record the mass of water in the flask.
Results are converted to volume by the given formula above.
3.Measuring cylinder calibration (50ml)
Calculate the water mass in the cylinder. Results will be converted to volume by using the formula given.
RESULTS & DISCUSSIONS
10 mL pipette
Trial 1Trial 2Trial 3
Actual volume (mL)11.89712.03811.887