# BLOGG # Agreement Of A Particular Value With The True Value

Example: the actual value of the mass of an iron cube is notoriously 7.90 g. The iron cube is weighed on 4 different electronic scales, and the percentage of relative error is calculated for each measurement as shown below: the random error will be smaller with a more accurate instrument (measurements are made in finer steps) and with more repeatability or reproducibility (accuracy). Consider a common laboratory experiment where you need to determine the percentage of acid in a vinegar sample by observing the volume of sodium hydroxide solution needed to neutralize a certain volume of vinegar. They lead the experiment and get value. Just to be safe, repeat the process on another identical sample of the same vinegar bottle. If you did it in the lab, you`ll know that it`s very unlikely that the second study will produce the same result as the first. If you perform a number of tests (i.e. identical in all respects), you will probably get scattered results. The reproducibility of a measurement is called accuracy. If all the measurements are very similar, we say that the determined value is well known. If we cannot get very similar measurements, we cannot say that the value is well known, but we say that the measurements are imprecise. A number of measurements can be described as accurate if the range of values is very small, i.e. the range close to 0 A number of measurements are described as inaccurate when the range of values is large, that is, the range is not close to 0.

For example, the iron cube has a real value of 7.90 ± 0.01 g, the real value is between 7.90 – 0.01 = 7.89 g and 7.90 + 0.01 = 7.90 g. An accurate value for the mass of iron is between 7.89 g and 7.91 g. An inaccurate value for the mass of iron would be less than 7.89 g or greater than 7.91 g. Since it is very rare for chemists to know exactly what the measurement is, they perform a series of measurements under the same conditions until they result in a series of measurements that coincide well. (1) The actual value of the volume of water in the piston is 50,00 ± 0,06 ml. This means that the actual value of the volume of water in the volumetric flask could be as low as 50.00 – 0.06 = 49.94 ml or equal to 50.00 + 0.06 = 50.06 mL. In order for the student`s measurements to be considered accurate, the determined value must be between 49.94 ml and 50.06 ml. .