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The Scientific Method: A logical series of steps scientists follow when solving problems.

The Scientific Method: A logical series of steps scientists follow when solving problems.

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The Scientific Method: A logical series of steps scientists follow when solving problems.

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  1. The Scientific Method:A logical series of steps scientists follow when solving problems.

  2. Orange Grove Experiment • Hypothesis:If we add fertilizer to the soil, then we will grow large oranges.

  3. Orange Grove • Purpose: Discover how to grow the biggest oranges.

  4. Example • The independent variables (manipulated variables) in the orange grove experiment could be: • Fertilizer • Other ideas? • The dependent variable (responding variable) is • Orange size • Other ideas? • Controlled Variables?

  5. Controlled Experiments • Controlled experiments only test one variable at a time • Independent Variable (manipulated variable) – is the variable being tested to see if a change occurs • Dependent Variables (responding variable) – are all of the observations and data you record during your experiment “DRY MIX” • Controlled Variables – are all of the other things that you must keep constant so they do not influence your results

  6. The SI System of Measurement(le Système International, SI)

  7. The Nature of Measurement A Measurement is a quantitative observation consisting of TWO parts • Part 1-number • Part 2-scale (unit) • Examples: • 20grams • 6.63 x 10-34Joule·seconds

  8. The Fundamental SI Units(le Système International, SI)

  9. SI PrefixesCommon to Chemistry

  10. K H D U D C M King Henry Died Unexpectedly Drinking Chocolate Milk

  11. Metric Conversions g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli Conversions in the metric system are merely a matter of moving a decimal point. The “base unit” means the you have a quantity (grams, meters, Liters, etc without a prefix.

  12. Metric Conversions g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli 1 2 3 18. L 18. liters = 18,000. mL Example #1: Convert 18 liters to milliliters

  13. Metric Conversions g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli 3 2 1 450. mg = 0.450 g 450.mg Example #2: Convert 450 milligrams to grams

  14. Metric Conversions g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli 2 3 1 4 5 6 20 kg 20 kg = 20,000,000 mg Example #3: Convert 20 kilograms to milligrams

  15. Uncertainty and Significant Figures Cartoon courtesy of Lab-initio.com

  16. Uncertainty in Measurement • A digit that must be estimatedis called uncertain. Ameasurementalways has some degree of uncertainty.

  17. Accuracy – how close a measurement is to the true value Precision – A) how close a set of measurements are to each other B) the detail of a number (for example, 3.00 g is more precise than 3 g) accurate & precise precise but not accurate not accurate & not precise 1.8

  18. Chemistry In Action On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mars’ atmosphere 100 km lower than planned and was destroyed by heat. 1 lb = 1 N 1 lb = 4.45 N “This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school, high school, and college science courses till the end of time.” One team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation. 1.7

  19. Significant Figures~Fast fingers~

  20. Rules for Counting Significant Figures (SigFigs)- Details • Nonzero integersalways count as significant figures. • 3456has • 4significant figures

  21. SigFigs – ZERO Details • Leading zerosnever count as significant figures. • 0.0486has • 3significant figures • 0.00000486has • 3significant figures

  22. SigFigs – ZERO Details • Captive zeros always count as significant figures. • 16.07has • 4significant figures

  23. SigFigs – ZERO Details • Trailing zeros are significant only if the number has a decimal point • 9.300has • 4significant figures • 2500 has • 2significant figures

  24. SigFigs • Exact numbers & equivalent statementshave an infinite number of significant figures. • 8 apples • 1inch=2.54cm, • exactly

  25. Can you summarize the rules for SigFigs?

  26. Sig Fig Practice #1 How many significant figures are in each of the following measurements? 24 mL 2 significant figures 4 significant figures 3001 g 0.0320 m3 3 significant figures 6.4 x 104 molecules 2 significant figures 560 kg 2 significant figures 1.8

  27. Sig Fig Practice #2 How many significant figures in each of the following? 1.0070 m  5 sig figs 17.10 kg  4 sig figs 100,890 L  5 sig figs 3.29 x 103 s  3 sig figs 0.0054 cm  2 sig figs 3,200,000 ns 2 sig figs

  28. Decimal Places

  29. 89.332 + 1.1 Shows the thousandths place Shows the hundredth place Only shows the tenth place Shows the ten thousandths place 90.432 Answer must match the least precise used, so round off to the tenth place: 90.4 Answer must match the least precise used, so round off to the hundredth place: 0.79 3.70 -2.9133 0.7867 Significant Figures – Mathematical Operation Rules for Addition or Subtraction The answer cannot have more digits to the right of the decimal point than any of the original numbers. (Answer must match the least precise number in the question.) 1.8

  30. 3 sig figs round to 3 sig figs 2 sig figs round to 2 sig figs 5 sig figs 5 sig figs Significant Figures - Mathematical Operation Rules for Multiplication or Division The number of significant figures in the result is set by the original number that has the smallest number of significant figures. (The answer must match the least # of sigfigs in the question.) 4.51 x 3.6666 = 16.536366 = 16.5 6.8 ÷ 112.04 = 0.0606926 = 0.061 1.8

  31. Rules for Significant Figures in Mathematical Operations • Multiplication and Division: Number of sig figs in the result equals the number in the least precise measurement used in the calculation. 6.38 x 2.0 = = 12.76 rounded to correct # of sigfigs: 13(2 sig figs)

  32. Sig Fig Practice #3 Calculation Calculator says: Answer 22.68 m2 3.24 m x 7.0 m 23 m2 100.0 g ÷ 23.7 cm3 4.22 g/cm3 4.219409283 g/cm3 0.02 cm x 2.371 cm 0.05 cm2 0.04742 cm2 710 m ÷ 3.0 s 236.6666667 m/s 240 m/s 5870 lb·ft 1818.2 lb x 3.23 ft 5872.786 lb·ft 2.9561 g/mL 2.96 g/mL 1.030 g ÷ 2.87 mL

  33. Sig Fig Practice #3 Calculation Calculator says: Answer 10.24 m 3.24 m + 7.0 m 10.2 m 100.0 g - 23.73 g 76.3 g 76.27 g 0.02 cm + 2.371 cm 2.39 cm 2.391 cm 713.1 L - 3.872 L 709.228 L 709.2 L 1821.6 lb 1818.2 lb + 3.37 lb 1821.57 lb 0.160 mL 0.16 mL 2.030 mL - 1.870 mL

  34. 6.64 + 6.68 + 6.70 = 6.67333 = 6.67 = 7 3 Significant Figures Exact Numbers Numbers from definitions or numbers of objects are considered to have an infinite number of significant figures. (They will not Limit the number of sigfigs in our answer.) The average of three measured lengths; 6.64, 6.68 and 6.70? Because 3 is an exact number 1.8

  35. 1000 mL 1L L2 1.632 L x = 1632 mL mL 1L 1.632 L x = 0.001632 1000 mL Dimensional Analysis Method of Solving Problems • Determine which unit conversion factor(s) are needed • Carry units through calculation • If all units cancel except for the desired unit(s), then the problem was solved correctly. • Round to proper number of sigfigs. How many mL are in 1.632 L? 1 L = 1000 mL (this statement has infinite sigfigs!) 1.9

  36. 1000 g 1kg 355 kg x = 355000 g Dimensional Analysis Method of Solving Problems • Determine which unit conversion factor(s) are needed • Carry units through calculation • If all units cancel except for the desired unit(s), then the problem was solved correctly. • Round to proper number of sigfigs. How many g are in 355 kg? 1 kg = 1000 g (this statement has infinite sigfigs!) 1.9

  37. 60 min m 343 x x x 1 mi 60 s s 1 hour = 767 1 min 1609 m mi hour The speed of sound in air is about 343 m/s. What is this speed in miles per hour? meters to miles seconds to hours 1 mi = 1609 m EXACTLY 1 min = 60 s EXACTLY 1 hour = 60 min EXACTLY • Determine which unit conversion factor(s) are needed • Carry units through calculation • If all units cancel except for the desired unit(s), then the problem was solved correctly. • Round to proper number of sigfigs. 1.9

  38. SCIENTIFIC NOTATION

  39. Scientific Notation In science, we deal with some very LARGE numbers: 1 mole = 602200000000000000000000 atoms In science, we deal with some very SMALL numbers: Mass of an electron = 0.000000000000000000000000000000091 kg

  40. Imagine the difficulty of calculating the mass of 1 mole of electrons! 0.000000000000000000000000000000091 kg x 602200000000000000000000 atoms ???????????????????????????????????

  41. Scientific Notation: A method of representing very large or very small numbers in the form: M x 10n n is an integer (Positive or negative) 1  M  10

  42. . 2 500 000 000 9 7 6 5 4 3 2 1 8 Step #1: Insert an understood decimal point Step #2: Decide where the decimal must end up so that one number is to its left Step #3: Count how many places you bounce the decimal point Step #4: Re-write in the form M x 10n

  43. 2 500 000 000 2.5 x 109 The exponent is positive because the decimal form of the number we started with was greater than 1.

  44. 0.0000579 1 2 3 4 5 Step #2: Decide where the decimal must end up so that one number is to its left Step #3: Count how many places you bounce the decimal point Step #4: Re-write in the form M x 10n

  45. 0.0000579 5.79 x 10-5 The exponent is negative because the decimal form of the number we started with was less than 1.

  46. Scientific notation expresses a number in the form: M x 10n n is an integer (Positive or negative) 1  M  10

  47. g m L 103 10-1 10-2 10-3 102 101 Metric Conversion Practice kilo hecto deka Base unit deci milli centi Liters 103 10-1 10-2 10-3 102 101 kL hL daL L Base Unit dL mL cL

  48. Problem #1 Convert400 mL to Liters L 400 mL 1 .400 L = 1 000 mL = 0.4 L 103 102 101 10-1 10-2 10-3 hecto = 4x10-1 L deci milli kilo deka centi Base unit

  49. Problem #2 Convert10 meters to mm mm 10 m 1 000 10 000 mm = 1 m = 1x104 mm 103 102 101 10-1 10-2 10-3 hecto deci milli kilo deka centi Base unit