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A. Measurement

QUANTITATIVE : How much? One subject 2 tusks Weight (or mass). QUALITATIVE : What is it? Gray Elephant White tusks Wide and large. www.clipartof.com. Measurements : Data that describe QUANTITATIVE and QUALITATIVE characteristics of matter. A. Measurement.

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A. Measurement

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  1. QUANTITATIVE: How much? • One subject • 2 tusks • Weight (or mass) • QUALITATIVE: What is it? • Gray Elephant • White tusks • Wide and large www.clipartof.com Measurements: Data that describe QUANTITATIVE and QUALITATIVE characteristics of matter A. Measurement

  2. Measurement: Chemistry Example Quantitative Added 25.0 mL of a solution containing 1.0 g of potassium iodide (KI) to 100.0 mL of a test solution thought to contain lead cations The precipitate (PbI2) was filtered out, dried, and its mass was 3.7 g. Assuming an excess of KI, this means the test solution contains 1.7 g lead (Pb) cations Qualitative The addition of potassium iodide (KI) to the test solution caused a YELLOW precipitate to form. This suggests the presence of lead (Pb) cations in the test solution

  3. Example: I drove 3.2 kilometers from home to work today. It took about 722 seconds to arrive. 3.2 km 722 s = 0.0044 km s B.Units • A UNIT tells what was measured 5.27 …….. WHAT? meters…now we know what and how much DERIVED UNITS….these come from multiplying or dividing base units

  4. Derived units • Remember that base units combined to form derived units provide another property description or characteristic • What I mean is…. Suppose I • Square a length unit Now I express area • Cube a length unit Now I express volume • Divide mass by volume Now I express density http://www.seed.slb.com/en/scictr/watch/gashydrates/images/cube2.jpg

  5. SI Units International System of Units (SI)

  6. Important Base and Derived units

  7. C. Using Scientific Measurements Precision and Accuracy Precise Accurate Precise Not Accurate Not Precise Not Accurate Not Precise Accurate There are methods to quantify HOW accurate and HOW precise…

  8. ZEROS • Zeros that are place holders are NOT • significant • Zeros between non-zero digits ARE • significant • Zeros at the END of a number are significant • IF the number has a decimal point II. Measurements and the Characteristics of Numbers • Significant Figures-digits with experimental meaning. All digits in a measurement are CERTAIN except the last which is understood to be UNCERTAIN or estimated 57.2574 CERTAIN UNCERTAIN • Rules 0.00100050300 100050300 Zeros NOT significant

  9. 78,200.9834 Round to 3 significant digits: 78,200 Round to 5 significant digits: 78,201 Round to 1 significant digits: 80,000 Round to 7 significant digits: 78,200.98 Concave meniscus Numbers: Rounding and Reporting Reporting: This burette is marked in 0.1 mL increments. How many significant digits AFTER The decimal point would you report?

  10. Math Operations with Sig Figs Multiplication and Division of numbers: The number of SIG FIGS in an answer should be reported with the least number of significant digits in any one of the numbers being multiplied, divided etc. 37.2872 x 45.3 ________ 1690 (Ouch! Seems harsh but those 6 SIG FIGS in the first number were ”killed” by the 3 SIG FIGS in the second number) Addition and Subtraction of numbers: The number of decimal places (not SIG FIGS ) in the answer should be the same as the least number of decimal places in any of the numbers being added or subtracted. 23.3456 +3.3 _______ 26.6 (3 SIG FIGS total but only 1 behind the decimal place)

  11. % ERROR Absolute value Average experimental value % error = | true value – expt value| x 100% true value AKA “accepted value” % error is a method of expressing the accuracy of the measurement By itself, it doesn’t say anything about the precision of multiple trials

  12. Scientific Notation • Why? • Would you rather write this: 6.023 x 1023 • Or THIS: 602,300,000,000,000,000,000,000 • FORMAT M x 10n Exponent is a whole number integer; can be (-) or (+) 1 ≤ M < 10 AND with the proper number of significant digits; can be (-) or (+) Base 10 number

  13. Proportions-Relationship of Variables A = kB A = k/C A is directly proportional to B when A B A Quotient of A and B is constant when A B B A is inversely proportionalto C Product of A and C is constant when A C A when A C C

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