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

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Activity No. 2
Reporting Measurements
Chemistry is a science based on measurement. A measurement tells us about a
property 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 an
instrument 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) a
unit of measurement.
The degree of agreement between the measured value and the true value is called
accuracy . The accuracy of a measured quantity is characterized by a) the number of
significant figures used to express the measured quantity and b) the specific reference to
the measurement uncertainty. For instance, the time it took Joe to walk from Swain to his
apartment was measured to be 35 seconds . By using two significant digits , we imply that
the time is uncertain to within ±1 second. The true time for Joe's walk was somewhere
between 34 and 36 seconds. Quoting the measurement as 35 seconds is different from
quoting it as 35.0 seconds ; the latter implies an uncertainty of ±0.1 second.
However, the accuracy of a measurement is limited by the precision of the
instrument . The precision of an instrument signifies the smallest quantity that the
instrument could be sensitive to or is able to detect. It is defined as half of the smallest
graduation 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 balance
have an uncertainty of ± 0.0001 g, while a top loading balance can read up to ± 0.1 g. If the

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instrument has a precision of ±0.05 g, the platform is sensitive up to 0.05 g only and is not
able 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 as
that 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 are incorrect!!!