Concepts & Connections 4th Edition by Charles H. Corwin

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1、Chapter 2Scientific Measurements1Vanessa N. Prasad-PermaulCHM 1025Valencia Community CollegeUncertainty in MeasurementsA measurement is a number with a unit attached.It is not possible to make exact measurements, thus all measurements have uncertainty.We will generally use metric system units. These

2、 include:The meter, m, for length measurementsThe gram, g, for mass measurementsThe liter, L, for volume measurements2Length MeasurementsLets measure the length of a candy cane.Ruler A has 1 cm divisions, so we can estimate the length to 0.1 cm. The length is 4.2 0.1 cm.Ruler B has 0.1 cm divisions,

3、 so we can estimate the length to 0.05 cm. The length is 4.25 0.05 cm.3Uncertainty in LengthRuler A: 4.2 0.1 cm; Ruler B: 4.25 0.05 cm.Ruler A has more uncertainty than Ruler B.Ruler B gives a more precise measurement.4 Uncertainty in MeasurementRuler A has an uncertainty of 0.1 cm, and Ruler B has

4、an uncertainty of 0.05 cm. Thus,(a) Ruler A can give the measurements 2.0 cm and 2.5 cm.(b)Ruler B can give the measurements 3.35 cm and 3.50 cm.SolutionWhich measurements are consistent with the metric rulers shown in Figure 2.2?(a) Ruler A: 2 cm, 2.0 cm, 2.05 cm, 2.5 cm, 2.50 cm(b) Ruler B: 3.0 cm

5、, 3.3 cm, 3.33 cm, 3.35 cm, 3.50 cmFigure 2.2 Metric Rulers for Measuring Length On Ruler A, each division is 1 cm. On Ruler B, each division is 1 cm and each subdivision is 0.1 cm.EXERCISE 2.1 Uncertainty in Measurement Which measurements are consistent with the metric rulers shown in Figure 2.2?(a

6、) Ruler A: 1.5 cm, 1.50 cm, 1.55 cm, 1.6 cm, 2.00 cm(b) Ruler B: 0.5 cm, 0.50 cm, 0.055 cm, 0.75 cm, 0.100 cmPractice ExerciseFigure 2.2 Metric Rulers for Measuring Length On Ruler A, each division is 1 cm. On Ruler B, each division is 1 cm and each subdivision is 0.1 cm.Mass MeasurementsThe mass of

7、 an object is a measure of the amount of matter it possesses.Mass is measured with a balance and is not affected by gravity.Mass and weight are not interchangeable.7Mass Versus WeightMass and weight are not the same.Weight is the force exerted by gravity on an object.8Volume MeasurementsVolume is th

8、e amount of space occupied by a solid, a liquid, or a gas.There are several instruments for measuring volume, including:Graduated cylinderSyringeBuretPipetVolumetric flask9Significant DigitsEach number in a properly recorded measurement is a significant digit (or significant figure).Significant digi

9、ts express the uncertainty in the measurement.When you count significant digits, start counting with the first nonzero number.Lets look at a reaction measured by three stopwatches.10Significant Digits, ContinuedStopwatch A is calibrated to seconds (1 s); Stopwatch B to tenths of a second (0.1 s); an

10、d Stopwatch C to hundredths of a second (0.01 s).11 Stopwatch A reads 35 s; B reads 35.1 s; and C reads 35.08 s. 35 s has two significant figure. 35.1 s has three significant figures. 35.08 has four significant figures. Significant DigitsIn each example, we simply count the number of digits. Thus,(a

11、)5(b)3(c)1(d)4Notice that the leading zero in (b) and (c) is not part of the measurement but is inserted to call attention to the decimal point that follows.SolutionState the number of significant digits in the following measurements:(a)12,345 cm(b)0.123 g(c)0.5 mL (d) 102.0 sEXERCISE 2.2 Significan