# Activity 2 Reporting Measurement CHEM.pdf - Activity No. 2...

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{PAGE\* MERGEFORMAT}Activity No. 2Reporting MeasurementsChemistry is a science based on measurement. A measurement tells us about aproperty of something. It may tell us how heavy an object is, or how hot, or how long it is.A measurement gives a number to that property. Measurements are always made using aninstrument of some kind such as rulers, stopwatches, weighing scales, and thermometers,and others. The result of a measurement is normally in two parts: (a) a number and (b) aunit of measurement.The degree of agreement between the measured value and the true value is calledaccuracy. Theaccuracyof a measured quantity is characterized by a) the number ofsignificant figures used to express the measured quantity and b) the specific reference tothe measurement uncertainty. For instance, the time it took Joe to walk from Swain to hisapartment was measured to be35 seconds. By using twosignificant digits, we imply thatthe time is uncertain to within ±1 second. Thetruetime for Joe's walk was somewherebetween 34 and 36 seconds. Quoting the measurement as 35 seconds is different fromquoting it as35.0 seconds; the latter implies an uncertainty of ±0.1 second.However, the accuracy of a measurement is limited by theprecision of theinstrument. Theprecision of an instrumentsignifies the smallest quantity that theinstrument could be sensitive to or is able to detect. It is defined as half of the smallestgraduation or calibration of the instrument.{EMBED Equation.DSMT4}The smallest calibration, SC, is given by the equation below{EMBED Equation.DSMT4}Some instruments have a given specifications. For instance, an analytical balancehave an uncertainty of ± 0.0001 g, while a top loading balance can read up to ± 0.1 g. If the
{PAGE\* MERGEFORMAT}instrument has a precision of ±0.05 g, the platform is sensitive up to 0.05 g only and is notable to detect weights of neither 0.01 g. nor 0.07 g.The number of digits after the decimal point in each reading should be the same asthat of the precision of the instrument. For instance, the reading will be:a.0.50{EMBED Equation.DSMT4}b.2.15{EMBED Equation.DSMT4}Hence, the following readings areincorrect!!!

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