READING GRADUATED EQUIPMENT Read each digit that is certain, plus one digit that is uncertain To determine the certain digits, identify the most accurate.

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Presentation transcript:

READING GRADUATED EQUIPMENT Read each digit that is certain, plus one digit that is uncertain To determine the certain digits, identify the most accurate graduations on the graduated equipment EX2-1 (of 15)

Most Accurate Graduations: One Celsius Degree Uncertain Digit: Tenths Place Reading : 47.6 Cº EX2-2 (of 15)

Most Accurate Graduations: Uncertain Digit: Reading : EX2-3 (of 15)

Most Accurate Graduations: One-Tenth of a Milliliter Uncertain Digits: Hundredths Place Reading : 9.37 mL EX2-4 (of 15)

Most Accurate Graduations: One Milliliter Uncertain Digits: Tenths Place Reading : 81.5 mL EX2-5 (of 15)

Most Accurate Graduations: Uncertain Digit: Reading : EX2-6 (of 15)

ACCURACY The extent to which a given measurement agrees with the standard value for that measurement Accuracy is affected by experimenter error and the equipment used to make that measurement EX2-7 (of 15)

6.81 cm 6.8 cm EX2-8 (of 15)

TOLERANCE For a graduated piece of equipment, it is the expected range of variation in a reading Tolerances for many graduated pieces of equipment are provided by the manufacturer 5-mL Volumetric Pipet :  0.02 mL When the tolerance is given, the last digit in the recorded reading should be in the same decimal place as the equipment’s tolerance Reading for a 5-mL Volumetric Pipet : 5.00 mL 5.00  0.02 mL EX2-9 (of 15)

To do this, (1)Determine what the most accurate graduations represent on the glassware (2)Divide the most accurate graduations by 2 to get the estimated tolerance of the graduated equipment If the tolerance of a graduated piece of equipment is not given, it can be estimated. EX2-10 (of 15)

Reading: 94.9ºC Most Accurate Graduations : 1 Cº Thermometer Tolerance: 1 Cº  2 = 0.5 Cº 94.9  0.5 ºC EX2-11 (of 15)

Reading: 60.0 mL Most Accurate Graduations : 1 mL Graduated Cylinder Tolerance: 1 mL  2 = 0.5 mL 60.0  0.5 mL EX2-12 (of 15)

PRECISION The extent to which a series of measurements agrees with each other Precision is affected by the experimenter EX2-13 (of 15)

Density of Lead : Trial g/mL Trial g/mL Trial g/mL Trial g/mL EX2-14 (of 15) not precise If an identifiable error caused the imprecision, the data can be ignored If no identifiable error caused the imprecision, the data can be only be ignored by using a statistical test (such as a Q-test)

Density of Lead : Trial g/mL Trial g/mL Trial g/mL Trial g/mL EX2-15 (of 15) Q = gap _________ range = – _________________ – = 0.89 If Q > Q 95%, then the data point can be ignored with 95% confidence