Accuracy is the proximity of a measure to fair value for this measurement. The accuracy of a measurement system refers to the proximity of the concordance between repeated measurements (repeated under the same conditions). Measurements can be both accurate and precise, accurate, but not precise, accurate, but not accurate, but not accurate or not. 32 MIXTURE and COMOUNDS MIXTURES PURE COMPOUNDSA mixture can be physically separated into compounds or pure elements. A pure assemblage has a constant composition with solid ratios of elements. Mixes can have a set of changing physical properties. For example, mixing alcohol and water cooked over a temperature range. Physical properties such as the point of ingion or the melting point of pure substances are invariant. For example, pure water is boiling at 100 degrees 1. 3 QUESTION Compliance of a given value to the actual value is a) Precision b) Precision c) Precision (d) Meaning e) Security 4 QUESTION Uncertainty in a measured quantity is determined by: a) the observer`s ability and the limits of the measuring instrument. b) neither the skill of the observer nor the limitations of the measuring instrument. c) the limits of the measuring instrument. (d) only the observer`s abilities.
e) none of them As noted above, the more measurements are made, the closer we can get to the actual value of a quantity. For several measurements (replications), 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 was no systematic error in the system. The average value deviates less from the « real value » as the number of measures increases. Technical errors can be divided into two categories: accidental errors and systematic errors. As the name suggests, random errors occur at regular intervals, with no apparent motive. Systematic errors occur when there is a problem with the instrument. For example, a scale could be poorly calibrated and read 0.5 g with nothing on it. All measures would therefore be overestimated by 0.5 g.
If you don`t take this into account to your extent, your measurement contains a few errors. 42 Exercise a. TC – TK 273 – 233 x 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 and Celsius scales, 233 K b. the helium graduation point, 4 K c. the temperature at which many chemical quantities are determined, 298K d. tungsten melting point, 3680 K a. TC – TK n 273 – 233 x 273 – -40 C TF – 9/5 × TC 32 – 9/5 × (-40.) – 32 – -40 F b.TC – C 9/5 × (-269) – 32 – -452 -F TC – 25 degrees Celsius; TF – × – 77 `F TC ` ` ` 3410 ` C; TF – 9/5 × – 6170 F All measurements are defective, which contributes to the uncertainty of the result.
Errors can be classified as human or technical error. Maybe you pass a small volume from one tube to another and you don`t get all the fullness in the second tube because you knocked it over: it`s a human error. 31 MIXTURE and COMOUNDS A MIXTURE is a combination of two or more substances that are not chemically combined and do not exist in fixed proportions relative to each other. Most natural substances are mixtures. An example of air is the mixture of several gases, oil, etc. Accidental error is reduced with a more precise instrument (measurements become thinner) and with more repeatability or reproducibility (precision).