Textbook Notes (369,100)
Canada (162,379)
Chemistry (50)
CHEM 111 (2)
Chapter 2

Chapter 2 Numbers from Measurements

6 Pages

Course Code
CHEM 111
Julie Lunniss

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Chapter 2Numbers from Measurements1 Measurementthe determination of the dimensions capacity quantity or extent of somethingThe most common in chemistry mass volume length time temperature pressure and concentrationTwo groups of numbers in scientific work 1 Exact numbera number with a value that is known exactly 2 Inexact numbera number that has a value with a degree of uncertainty in itIt is impossible to make an exact measurement due to flaws in measuring devices improper instrument calibration and the lack of skills possessed by the person making the measurement23 Accuracy Precision and ErrorAccuracyan indicator of how close a measurement or the average of many measurements comes to a true or accepted value Precisionan indicator of how close a series of measurements on the same object are to each otherPrecision and accuracy both usually relate directly tothe physical measuring device usedRandom erroran error originating from uncontrollable variables in an experimentEg momentary changes in air currents or temperature near a sensitive balance for weighing The net result of random errors is a decrease in precision of a series of measurementsSystematic erroran error originating from controllable variables in an experiment results consistently too high or low compared to the true valueEg a flaw in a piece of equipment such as a chipped weight in a balanceAffects the accuracy of measurements24 Uncertainty in MeasurementsOnly one estimated digit is recorded as part of a measurement The value 29247 contains two estimated digits the 4 and 7 and indicates a measurement with smaller uncertainty than is obtainable with the thermometer Magnitude of the uncertainty in the last recorded digit the estimated digit is indicated by anotation151 grams The measurement 151 grams designates a mass 1501 grams that lies between 14 and 16 grams The mass that 15003 grams lies within this range isnt known The measurement15003 grams denotes a mass between 1531 and1537 grams with the mass between this range not being known
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