Ch. 3 Scientific Measurement

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 gt 10 exponent is
• numbers lt 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
• Bulls eye accurate precise
• All same spot not near bulls eye precise
• 1 bulls 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 _at_ end to left of understood
  decimal are not sig 1200

13
Unlimited Sig Figures

• Counting
• If its 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 its 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 lt than on earth
• force of gravity 6x gt 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) _at_ 4?C
• a cube of H2O _at_ 4?C measuring 10cm on each side
  a volume of 1L
• mass of 1 cm3 H2O _at_ 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 _at_ 4?C 1 g/cm3 (Density reference)
• Specific gravity (s.g.) Density of substance
  (g/cm3)
• Density of H2O (g/cm3)