Chapter 2.3 : Using Scientific Method

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Chapter 2.3 : Using Scientific Method

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

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