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Scientific Measurement

Scientific Measurement. Objective: To understand the importance of measurements in Chemistry. Measurements. Quality with both number and a unit History 4000Bc- Egyptians used knotted cords- kite 1700Bc- Babylonians used cubits- elbow to finger tip

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Scientific Measurement

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  1. Scientific Measurement Objective: To understand the importance of measurements in Chemistry

  2. Measurements • Quality with both number and a unit • History • 4000Bc- Egyptians used knotted cords- kite • 1700Bc- Babylonians used cubits-elbow to finger tip • 500Bc- Phoenicians used Zebo-finger width • 300Bc- Romans used a soldiers Boot as a unit-equal to width of 12 fingers • 900AD- due to trade a standard unit of measurement was needed -Fathom- finger tip to finger tip (Vikings) • 1500AD- Tudor rules create a furlong= 220cyd Queen Elizabeth I- Roman mile= 5280 ft= 8 furlongs 1790AD- Metric system was proposed- base 10 system, meter basic uni1 1875AD- Renamed International System of Units (SI)

  3. Scientific Notation • Since we deal w/ numbers very small and large 5.75 x 104 Coefficient Base Exponent • 1. The coefficient must be greater than or equal to 1 and less than 10.2. The base must be 10.3. The exponent must show the number of decimal places that the decimal needs to be moved to change the number to standard notation.  A negative exponent means that the decimal is moved to the left when changing to standard notation. Positive to the right

  4. Accuracy/Precision • Accuracy- a measure of how close a measurement comes to the actual or true value of whatever is measured • Precision- a measure of how close a series of measurements are to one another • How do we test accuracy?? • How to we test precision?? • Dart board example

  5. Error • Accepted Value-correct value based on reference sources • Experimental Value- measured in the lab • Error = EV-AV • Percent Error = [ error] x 100% Accepted value

  6. What are Significant Figures? • All the digits that can be known precisely in a measurement, plus a last estimated digit. • “Guess Digits” • 10 mL graduated cylinder=8.29 • 25 mL graduated cylinder=20.55 • 100 mL graduated cylinder= 55.5 • Cm Ruler = 2.55

  7. Why do we use Sig Figs? • We need to know how precise our measurements are. • Our calculations can not be more precise than the instruments we used to measure them • When working in the chemistry lab it is important to understand where your measurement came from

  8. Significant Figure Rules! • 1. Every non-zero digit in a reported measurements is assumed to be significant • 27.3 m = 3 significant figures 0.734m = 3 Sig Figs • 2. Zeros appearing between nonzero digits are significant • 2703 m = 4 Sig Figs 70003 m = 5 Sig Figs • 3. Left most zeros appearing infront of nonzero digits are not significant, they act as placeholders • 0.0056 = 2 Sig Figs 0.4202 = 4 Sig Figs

  9. Cont. • 4. Zeros at the end of the number and to the right of the decimal point are always significant. • 43.00 = 4 Sig Figs 1.0110= 5 Sig Figs • 5. Zeros at the rightmost end of a number but to the left of the decimal are not significant, they act as place holders • 21,800 = 3 Sig Figs 7,000 = 1 Sig fig

  10. Atlantic/Pacific Method • Another way of looking at it………. Pacific Side Atlantic Side (Decimal is Present) (Decimal is Absent) NUMBER If the decimal is Present you come in from the left hand side and count every digit as significant starting with the first nonzero digit • 1.002 = 4 Sig Figs 108.008 = 6 Sig Figs

  11. Atlantic/Pacific Cont. • If the decimal is Absent, then you come in from the right hand side and count every digit as significant starting with the first nonzero digit • 1239 = 4 Sig Figs 12000 = 2 Sig Figs 300 = 1 Sig Fig

  12. Significant Figures when Adding or Subtracting • Think…”You are only as strong as your weakest link” • Your answer can only have the same number of decimal places as the number with the least amount of decimal places • 3.0001 + 2.33 Weakest link 5.3301 Since our weakest link only has 2 decimal places our answer can only have 2 decimal places…….so round the answer to 5.33

  13. Significant figures when multiplying or dividing • Again..think, “Your only as strong as your weakest link” • Your answer needs to have the same amount of significant figures as the number with the least amount of sig figs • 3.444 x 2.04 = 7.02576 Since our “weakest link” only has 3 sig figs, our answer can only have 3 sig figs Weakest Link

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