Accuracy indicates how close a measurement is to the appropriate value for that measurement. The accuracy of a measurement system is related to the close adequacy between repeated measurements (repeated under the same conditions). Measurements can be precise and precise, accurate, but not precise, precise, but not precise or neither. The accidental 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. 42 Exercise a. TC = TK 273 = 233 273 = -40 °C56. Convert the following kelvin temperatures to degrees Celsius and Fahrenheit.
a. the temperature that records the same value on both the Fahrenheit scale and the Celsius scale, 233 K b. the boiling point of helium, 4 K c. the temperature at which many chemical sizes are determined, 298 K d. the tungsten melting point, 3680 K a. TC = TK 273 = 233 273 = -40 °C TF = 9/5 × TC + 32 = 9/5 × (-40.) + 32 = -40 °F b.TC = = =°C; TF = 9/5 × (-269) + 32 = -452 °F TC = = = 25 °C; TF = × = 77 °F TC = = 3410 °C; TF = 9/5 × = 6170 °F All measurements are subject to errors contributing to the uncertainty of the result. Errors can be classified as human error or technical failure. Maybe you transfer a small volume from one tube to another and you don`t quite get the total amount in the second tube because you knocked it over: it`s human error.
32 MIXTURES AND COMOUNDS MIXTURES THE MIXTURE OF PURE COMPOUNDS MAY be physically separated into pure compounds or elements. A pure compound has a constant composition with fixed conditions of elements. Mixtures may exhibit a changing amount of physical properties. For example, a mixture of alcohol and water boils over a temperature range. Physical properties such as boiling point or melting point of raw materials are invariant. For example, pure water boils at 100 degrees oC. As mentioned above, the more measurements there are, the closer we can get to the actual value of a quantity. With multiple measures (replicates), we can evaluate the accuracy of the results and then use simple statistics to estimate how close the average value would be to the actual value if there were no systematic error in the system. The average differs less from the «actual value» as the number of measurements increases. 3 QUESTION The conformity of a given value with the actual value is defined as a) accuracy b) error c) Accuracy d) Significance e) Safety 4 QUESTION The height of the uncertainty in a measured face is determined by: a) the capacity of the observer and the limits of the measuring instrument. (b) neither the capabilities of the observer nor the limitations of the measuring instrument.
(c) only the limitations of the measuring instrument. (d) only the capabilities of the observer. (e) None of these technical errors can be divided into two categories: accidental error and systematic error. . . .