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Scientific Method and Units of Measurement in Chemistry

This chapter explores the scientific method, including observing and collecting data, formulating hypotheses, testing hypotheses, and theorizing models. It also covers units of measurement in chemistry, focusing on SI measurement and derived SI units, as well as conversion factors and significant figures.

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Scientific Method and Units of Measurement in Chemistry

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  1. Chapter 2 Measurements and Calculations

  2. Sect. 2-1: Scientific Method • Scientific Method • Observing and collecting Data • Qualitative and Quantitative • Formulating Hypothesis • Testing hypothesis • Theorizing

  3. Model • Theory

  4. Sect. 2-2: Units of Measurement • SI Measurement • Le Systéme International d’Unités (International System of Units)

  5. 7 SI Base Units • Mass – kilogram (kg) • Length – meter (m) • Time – second (s) • Temperature – Kelvin (K) • Amount of substance – mole (mol) • Electric current – ampere (A) • Luminous intensity – candela (cd)

  6. SI Prefixes • See page 35 in textbook

  7. Derived SI units • Volume • Cubic meter (m3) is very large, so cubic centimeters (cm3) is usually used instead • cm3 is equal to one mL, so they can be used interchangeably.

  8. Density • D=mass/volume • Units typically used are g/cm3 or g/mL

  9. Conversion Factors • Ratio derived from the equality of 2 different units • used to convert from one unit to the other • Ex.: 1 min or 60 sec 60 sec 1 min

  10. How many seconds are in 5 minutes? (Work problem by using dimentional analysis/conversion factors.) • 5.712g is equal to how many milligrams?

  11. Sect. 2-3: Using Scientific Measurements • Accuracy vs. Precision http://images.google.com/imgres?imgurl=http://www.studyphysics.ca/newnotes/20/unit01_kinematicsdynamics/chp02_intro/images/neither.GIF&imgrefurl=http://www.studyphysics.ca/newnotes/20/unit01_kinematicsdynamics/chp02_intro/lesson02.htm&h=176&w=178&sz=2&hl=en&start=8&tbnid=-MXNdAPx2LHv8M:&tbnh=100&tbnw=101&prev=/images%3Fq%3Ddart%2Bboard%2Baccuracy%2Band%2Bprecision%26gbv%3D2%26svnum%3D10%26hl%3Den

  12. Percent Error • % error =Accepted-Experimental x 100 Accepted • Some error in measurements can be expected due to precision of instruments

  13. Significant figures • Sig figs are based on instrument precision (numbers can only be as exact as the instrument is)

  14. Rules for Sig figs: • Skip over zeroes at the side you start counting on • If it has a decimal, count from the left • If it doesn’t have a decimal, count from the right • Once you start counting, count everything (even zeroes)

  15. Example: How many sig figs are in the number 547.03? • 5 sig figs

  16. Example: How many sig figs are in the number 5,400? • 2 sig figs

  17. Rounding with Sig Figs • When adding/subtracting, answer will be rounded to least number of decimal places • When multiplying/dividing, answer will be rounded to least number of sig figs

  18. When using conversion factors, refer to the “given” number to determine number of sig figs for the answer

  19. Scientific Notation • Convert .000872 to scientific notation • 8.72 x 10-4

  20. Convert 436289 to scientific notation. • 4.36289 x 105

  21. Scientific Notation by using the calculator • Use “EE” or “exp” key on your calculator to replace “ x 10^” • Ex: 8.72 x 10-4 would be 8.72”EE”-4

  22. Direct Proportions • Dividing two quantities by each other gives a constant value http://images.google.com/imgres?imgurl=http://homepage.mac.com/cbakken/proportions/image27.gif&imgrefurl=http://homepage.mac.com/cbakken/proportions/patterns3.html&h=204&w=281&sz=3&hl=en&start=1&tbnid=ht5Oe573XV4IDM:&tbnh=83&tbnw=114&prev=/images%3Fq%3Ddirect%2Brelationship%2Bgraph%26gbv%3D2%26svnum%3D10%26hl%3Den%26sa%3DG

  23. Inverse Proportions • Multiplying two quantities by each other gives a constant value http://images.google.com/imgres?imgurl=http://homepage.mac.com/cbakken/proportions/image27.gif&imgrefurl=http://homepage.mac.com/cbakken/proportions/patterns3.html&h=204&w=281&sz=3&hl=en&start=1&tbnid=ht5Oe573XV4IDM:&tbnh=83&tbnw=114&prev=/images%3Fq%3Ddirect%2Brelationship%2Bgraph%26gbv%3D2%26svnum%3D10%26hl%3Den%26sa%3DG

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