The concentration of a sodium hydroxide solution is determined by titration against a standard solution of oxalic acid.
The
absolute error in the calculated
concentration of sodium hydroxide can be
determined from the error in each of the measurements made during the determination.
These are mass of the oxalic acid dihydrate (1.5432), the volume of the volumetric flask used to make the standard solution (250
), and the volumes delivered by the pipette (20.00
) and the burette (21.76
).
The
absolute error in each measurement depends on the manufacturer's specification for the piece of equipment used and has the unit of the measurement. To find the absolute error in the calculated concentration (0.04896
), the errors in four measurements must be combined. To do this, follow the steps below. An example is given underneath.
Convert each absolute error to a percentage error using error in the measurement specified by the manufacturer.
Add the percentage errors.
Multiply the decimal equivalent of the percentage error by the concentration.
Round the absolute error to one significant figure.
Round the calculated concentration so that the last digit is in the same decimal place as the absolute error.
| Quantity measured | Magnitude of
measurement | Absolute error | % error |
| mass of oxalic acid | 1.5432 g | balance
±0.0002 g | | 0.0002 g | × 100% = 0.013 % | | 1.5432 g | |
| volume of flask | 250.0 mL | volumetric flask
±0.2 mL | | 0.2 mL | × 100% = 0.080 % | | 250 mL | |
| pipette volume | 20.00 mL | pipette
±0.04 mL | | 0.04 mL | × 100% = 0.200 % | | 20 mL | |
| titre volume | 21.76 mL | burette
±0.2 mL | | 0.04 mL | × 100% = 0.184 % | | 21.76 mL | |
| Total percentage error in concentration | (0.013 + 0.080 + 0.200 + 0.184)% = 0.477% |
| Absolute error in concentration | | 0.477 | × 0.04896 mol L–1 = 0.0002 mol L–1 | | 100 | |
| Report oxalic acid concentration as | 0.0490 ± 0.0002 mol L–1 |