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Chapter 2.3 : Using Scientific Method
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Chapter 2.3 : Using Scientific Method

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  • 1. Using scientific measurements
    SECTION 2-3
  • 2. Objectives
    Distinguish between accuracy and precision
    Determine the number of significant figures in measurements
    Perform mathematical operations involving significant figures
    Convert measurements into scientific notation
    Distinguish between inversely and directly proportional relationships
  • 3. Accuracy and Precision
    Accuracy – the closeness of measurements to the correct or accepted value of the quantity measured
    Precision – the closeness of a set of measurements of the same quantity made in the same way.
  • 4. Percent Error
    Calculated by subtracting the experimental value from the accepted value, dividing the difference by the accepted value, and then multiplying by 100
    Percent error = valueaccepted - valueexperimental x 100
    valueaccepted
  • 5. Error in Measurement
    Observer
    Equipment
    Conditions
  • 6. Significant Figures
    Consists of all digits know with certainty, plus one final digit
  • 7. Rules for determining significant zeros
    Digits from 1-9 are always significant.
    Zeros between two other significant digits are always significant
    One or more additional zeros to the right of both the decimal place and another significant digit are significant.
    Zeros used solely for spacing the decimal point (placeholders) are not significant.
  • 8. Rounding
    Greater than 5 inc. by 1 42.68  42.7
    Less than 5 stay 17.32  17.3
    5, followed by nonzero inc. by 1 2.7851  2.79
    5, not followed by nonzero inc. by 1 4.635  4.64
    Preceded by odd digit
    5, not followed by nonzero stays 78.65 78.6
    Preceded by Even digit
  • 9. Addition/subtraction with significant figures
    The answer must have the same number of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point.
    35. 1
    + 2.3456
    37.4456
    So : 37.4
  • 10. Multiplication/Division with significant figures
    The answer can have no more significant figures than are in the measurement with the fewest number of significant figures.
    3.05 g ÷ 8.470 mL = 0.360094451 g/mL
    3 s.f. 4 s.f. Should be 3 s.f.
  • 11. Scientific Notation
    Numbers are written in the form M x 10n, where the factor M is a number greater than or equal to 1 but less than 10 and n is a whole number.
    65 ooo km
    M is 6.5
    Decimal moved 4 places to left
    X 104
    So: 6.5 x 104 km
    Why? Makes very small or large numbers more workable
    60 200 000 000 000 000 000 000 molecules
    6.02 x 1023 molecules
  • 12. Scientific Notation
    Extremely small numbers – negative exponent
    Ex: 0.0000000000567 g
    5.67 x 10-11 g
    M should be in significant figures
    • 4.2 x 104 + 7.9 x 103 =
    • 13. 5.o x 104
  • Direct Proportions
    Two quantities if divided by the other gives a constant value
    If one doubles so does the other
    y = kx
  • 14. Inverse Proportions
    Two quantities who’s product is a constant
    If one doubles, the other is cut in half
    xy = k

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