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MEASUREMENT Units of Measurement

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Types of Data Data refers to information Qualitative Data Describes something Texture, Color, etc Quantitative Data Measures Something Length, Mass, Time, etc

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Determine if each of the following is a qualitative or quantitative measurement. A.The sandwich has ham in it. B.There are four eggs in the carton. C.I used 230 grams of NaOH. D.I added water to the solution.

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Measurement A quantity with both a NUMBER and a UNIT Provides a reference point NO NAKED NUMBERS!

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Number vs. Quantity Quantity = number + unit

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Measurements Accuracy How close a measurement comes to the accepted answer Precision How close a series of measurements are to each other. How specific an measurement is 10 vs. 10.01 vs. 10.007

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Let’s use a golf analogy

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Accurate?No Precise?Yes

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Accurate?Yes Precise?Yes

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Precise?No Accurate?No

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Accurate?Yes Precise?We can’t say!

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Accurate? Precise?

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Error Accepted value – The right answer Based on reliable references Also called Theoretical Yield Experimental Value- what you get in lab Also called Actual Yield

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Measurements Determining Error How far your measurement is from the accepted value.

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Percent Error

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International System of Measurements MeasurementSI Base UnitSymbol LengthMeter m MassKilogram kg TemperatureKelvin K TimeSecond s AmountMole mol Light IntensityCandela cd Electric CurrentAmpere A

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mega-M10 6 deci-d10 -1 centi-c10 -2 milli-m10 -3 PrefixSymbolFactor micro- 10 -6 nano-n10 -9 pico-p10 -12 kilo-k10 3 BASE UNIT---10 0

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Significant Figures or Digits Significant Figures (sig figs) are all digits which show where an actual measurement is made; the more sig figs, the better the measurement: 0.5 m (1 sig fig) 0.50 m (2 sig figs) 0.500 m (3 sig figs) 0.500 m was measured with a more accurate ruler

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Counting Sig Figs Which digits are significant? 1.All non-zeroes are significant 2.A final zero after a decimal point is significant 3.All zeroes between sig figs are significant 4.Zeroes that are place holders are not significant and do not go into scientific notation

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How many sig figs in the following measurements? 1.770 mL 2.0.0700 mL 3.7070 mL 4.0.007 mL 5.7.00 x 10 3 mL 6.7000 mL 7.70.070 mL 8.77.0 mL 1.2 2.3 3.3 4.1 5.3 6.1 7.5 8.3

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Math with Sig Figs Addition & Subtraction The answer must be rounded to the same number of decimal places as the measurement with the fewest decimal places (worst measurement). 527.38 m + 21.2 m 548.58 m 548.6 m

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Math with Sig Figs Multiplication & Division The answer must be rounded to the same number of sig figs as the measurement with the fewest sig figs (worst measurement). 527.38 m (5) x 21.2 m (3) 11180.456 m 2 11200 m 2 (3)

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Scientific Rounding Rules 1. If the digit to be rounded is followed by 0,1,2,3, or 4 – do not round the digit / leave digit alone 2. If the digit to be rounded is followed by 6,7,8, or 9 – round up the digit 3. If the digit to be rounded is followed by a 5 with any digits of value anywhere behind the 5 – round up the digit 4. If the digit to be rounded is followed by only a 5 or a 5 with no numbers of value behind the 5 – odd digits round up and even digits are left alone

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Round the following measurements to 2 sig figs: 1.32980 g 2.0.07810 m 3.355 mL 4.345 mL 5.798 o C 6.5.92 x 10 24 atoms 7.1450.01 km 1.33000 g 2.0.078 m 3.360 mL 4.340 mL 5.8.0 x 10 2 o C 6.5.9 x 10 24 atoms 7.1500 km

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