Buret calibration curve

Using either a pipet or a buret, quantities of standard solutions are measured. (If a buret is used, separate measurements of the initial and final volumes are needed.) Solvent may be added to dilute the samples if needed. These are the known solutions from which a calibration curve will be constructed. 

What does this mean Suppose that Figure 3-3 applies to your buret. If you begin a titration at 0.04 mL and end at 29.00 mL, you would deliver 28.96 mL if the buret were perfect. Figure 3-3 tells you that the buret delivers 0.03 mL less than the indicated amount, so only 28.93 mL were actually delivered. To use the calibration curve, either begin all titrations near 0.00 mL or correct both the initial and the final readings. Use the calibration curve whenever you use your buret. 

Figure 3-3 Calibration curve for a 50-mL buret. The volume delivered can be read to the nearest 0.1 mL. If your buret reading is 29.43 mL, you can find the correction factor accurately enough by locating 29.4 mL on the graph. The correction factor on the ordinate (y-axis) for 29 4 mL on the abscissa (x-axis) is 0.03 mL (to the nearest 0.01 mL).

Another systematic error arises from an uncalibrated buret. The manufacturer s tolerance for a Class A 50-mL buret is 0.05 mL. When you think you have delivered 29.43 mL, the real volume could be anywhere from 29.38 to 29.48 mL and still be within tolerance. One way to correct for an error of this type is to construct a calibration curve, such as that in Figure 3-3, by the procedure on page 38. To do this, deliver distilled water from the buret into a flask and weigh it. Determine the volume of water from its mass by using Table 2-7. Figure 3-3 tells us to apply a correction factor of —0.03 mL to the measured value of 29.43 mL. The actual volume delivered is 29.43 — 0.03 = 29.40 mL. 

A buret is calibrated by filling with water to the zero mark, withdrawing to the 25 ml mark, and weighing the water withdrawn From the following data, compute the correction that must be applied at the 25 ml mark (similar corrections at other intervals may be used to construct a correction curve for the entire range of the buret)... 

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