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Ch. 3 Scientific Measurement

Ch. 3 Scientific Measurement. 3.1 The Importance of Measurement. Qualitative &Quantitative Measurements. qualitative descriptive big, small, hard, soft quantitative numbers & units numeric data - 100  , 50g. Scientific Notation. in sci. not. A # is written as the product of 2 #s

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Ch. 3 Scientific Measurement

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  1. Ch. 3 Scientific Measurement

  2. 3.1 The Importance of Measurement

  3. Qualitative &Quantitative Measurements • qualitative • descriptive • big, small, hard, soft • quantitative • numbers & units • numeric data - 100, 50g

  4. Scientific Notation • in sci. not. A # is written as the product of 2 #s • a coefficient & a 10 to a power • 6.02 * 1023 • allows uniform way to represent #s • easier for really big & really small #s • numbers > 10 exponent is + • numbers < 10 exponent is –

  5. Multiplication in Sci Note • Multiply the coefficients & add exponents • (3.0 * 103) * (2.0 * 102) = 6.0 * 105

  6. Division in Sci Note • Divide the coefficients & subtract the exponents • (9.0 * 103) / (3.0 * 101) = 3.0 * 102

  7. Addition & Subtraction in Sci Note • Make exponents the same • This aligns the decimal points • Then add or subtract coefficients • (6.02 * 1023) + (1.00 * 1025) = • 6.02 * 1023 + 100.00 * 1025

  8. 3.2 Uncertainty in Measurements p. 54

  9. Accuracy, Precision • Accuracy – how close to actual or true value • Precision – how close a series of measurements are to each other • Ex. Dart board • Bull’s eye – accurate & precise • All same spot not near bull’s eye – precise • 1 bull’s eye & 2 others – 1 accurate & poor precision

  10. Error • Accepted value – correct value • Experimental value – measured value • Error = experimental value – accepted value • Percent error • Use absolute value of error to make +

  11. Significant Figures in Measurements • include all known (measured) figures + 1 estimated • Allow common language for communicating numbers

  12. Rules for Sig Fig • Every non-zero digit is sig – 123.5 • Zeroes between non-zero digits are sig – 1002 • Zeroes at the end of a # to right of decimal are sig – 123.500 • Leftmost zeroes in front of non-zero # are not sig – 0.005 • Rightmost zeroes @ end to left of understood decimal are not sig – 1200

  13. Unlimited Sig Figures • Counting • If it’s an exact count • Ex. Count 20 students in class • Exactly Defined Quantities • 60 minutes in 1 hour • 24 hours in 1 day

  14. Significant Figures in Calculations • calculated figure cannot be more precise than measurements from which it’s calculated • round answer to correct sig fig

  15. Rounding Sig Fig • if digit immediately to the right of the last sig digit is less than 5, all numbers including it (to the right) are dropped & the digit stays the same • if the digit to right is  5 then round the last sig fig up to 1 • option • if the digit to the right = 5 and not followed by a zero then if odd, round up or if even, do not round • different books have different opinions • idea behind this option is to give you equal weight

  16. Addition & Subtraction • Round to same # of decimal places as the measurements w/ least (not digits)

  17. Multiplication & Division • Round to same # of sig fig as the measurement w/ the least

  18. 3.3 International System of Units • Units of Measurement – p.63 Table 3.1 • Common Prefixes – p.64 Table 3.2 • Metric Length – p.64 Table 3.3 • Metric Volume – p.65 Table 3.4

  19. Units of Length • Metric System • Base of 10 • Convert easily • SI – International System of Units • Basic unit = meter • linear measure

  20. Units of Volume • volume – space occupied by a sample of matter • basic unit = cubic meter (m3) • volumetric glassware (* more accurate) • *pipet or buret • *volumetric flask • graduated cylinder • beaker • Erlenmeyer flask

  21. Units of Mass • astronaut on moon is 6x < than on earth • force of gravity 6x > on earth than on moon • weight = force that measures the pull on a given mass by gravity • mass = measure of quantity of matter • basic SI unit = 1 kg • 1 kg = 1 L of H20(l) @ 4C • a cube of H2O @ 4C measuring 10cm on each side = a volume of 1L • mass of 1 cm3 H2O @ 4C = 1g

  22. 3.4 Density p. 68

  23. Determining Density • ratio of mass to volume • density = mass / volume • units = g/cm3

  24. Density Cont. • less dense floats on more dense • as temp increases • volume increases (most substances) • mass remains same • density decreases

  25. Specific Gravity • comparison of D of a substance w/ D of a reference substance • H2O @ 4C = 1 g/cm3 (Density reference) • Specific gravity (s.g.) = Density of substance (g/cm3) • Density of H2O (g/cm3)

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