Pipettes are indispensable tools often used in chemical laboratories to measure and transfer a precise amount of liquid. These are essentially instruments consisting of a narrow tube with a rubber bulb (Peleo's ball) at the top. The tube is graduated from top to bottom, typically at ten millimeter intervals. Absolute accuracy is required when making a pipette measurement, because any discrepancy in the reading can affect the result of the chemical reaction. To ensure accuracy, pipettes should be calibrated at regular intervals. Periodic calibration is also desirable for the most advanced and sophisticated instruments, as many factors can affect the accuracy of measuring instruments over time. The calibration process verifies whether the instrument offers a correct measurement, so that it can be adjusted over time to maintain the efficiency of experiments or laboratory tests.
Steps
Step 1. Clean the pipette
Thoroughly clean the pipette and beaker, then dry them thoroughly. This is done to eliminate any previous residues that could affect the results.
Step 2. Add distilled water
Put some distilled water in a flask. Let it sit on a table for about 15 minutes, then measure the water temperature.
Step 3. Measure the mass of the beaker
Calculate the mass of the beaker to the nearest tenth of a milligram using a balance.
Step 4. Help yourself with a filler
Now, using a pipette filler, fill the pipette with the water from the flask. Pour this water into the glass. Weigh the glass again. Take note of the difference in weight of the glass and calculate the mass of water discharged. Repeat this procedure three more times.
Step 5. Proceed with the calculations
Calculates and averages the four pipette measurements.
Step 6. Make adjustments based on the principle of buoyancy in air
Add 1.06 mg per gram to the average mass, to adjust it for buoyancy in air during weighing. In case you are using a digital scale, skip this step.
Step 7. Calculate the density of the water
Calculate the density of the water at the temperature you measured earlier. Determine the average volume of water discharged from the pipette using the formula: Volume = mass / density.
Step 8. Compare the calculations and measurements
To check the accuracy of the pipette, compare your measurements and calculations with other pipette calibration results.
