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# Lecture 3.1- Measurements (P)

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Section 3.1 lecture for Prep Chemistry

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• The distribution of darts illustrates the difference between accuracy and precision. a) Good accuracy and good precision: The darts are close to the bull&amp;#x2019;s-eye and to one another. b) Poor accuracy and good precision: The darts are far from the bull&amp;#x2019;s-eye but close to one another. c) Poor accuracy and poor precision: The darts are far from the bull&amp;#x2019;s-eye and from one another.
• The scale below has not been properly zeroed, so the reading obtained for the person&amp;#x2019;s weight is inaccurate. There is a difference between the person&amp;#x2019;s correct weight and the measured value. Calculating What is the percent error of a measured value of 114 lb if the person&amp;#x2019;s actual weight is 107 lb?
• Three differently calibrated meter sticks are used to measure the length of a board. a) A meter stick calibrated in a 1-m interval. b) A meter stick calibrated in 0.1-m intervals. c) A meter stick calibrated in 0.01-m intervals. Measuring How many significant figures are reported in each measurement?
• ### Lecture 3.1- Measurements (P)

1. 1. Lecture 3.1 and 3.2- Measurements
2. 2. SCIENTIFIC NOTATION is used to represent very large or very small numbers
3. 3. SCIENTIFIC NOTATION 6.02 x 1023
4. 4. SCIENTIFIC NOTATION 6.02 x 1023 must be between 1-10
5. 5. SCIENTIFIC NOTATION 6.02 x 1023 must be The power of ten between determines the size of 1-10 the number
6. 6. SCIENTIFIC NOTATION 6.02 x 1023 must be The power of ten between determines the size of 1-10 the number Positive power = big number(greater than 10) Negative power = small number(less than one)
7. 7. SCIENTIFIC NOTATION 6.02 x 1023 must be The power of ten between determines the size of 1-10 the number Positive power = big number(greater than 10) Negative power = small number(less than one) EX. 0.00567g = 5.67 x 10-3g a small number 437,850g = 4.3785 x 105g a large number
8. 8. To convert from standard notation to scientific notation move the decimal point to make a number between 1 and 10 then count how many spaces you moved it. positive because it is a big number negative because it is a small number
9. 9. Accuracy and Precision • Accuracy measures how close a measurement comes to the actual value. • Precision measures how close a series of measurements are to each other.
10. 10. 3.1
11. 11. Just because a measuring device works, you cannot assume it is accurate. The scale has not been properly zeroed, so the reading obtained for the person’s weight is inaccurate.
12. 12. Significant digits When measuring we record all certain digits plus one uncertain digit
13. 13. Significant digits When measuring we record all certain digits plus one uncertain digit, so there is always some degree of uncertainty in measurement.
14. 14. Significant digits When measuring we record all certain digits plus one uncertain digit, so there is always some degree of uncertainty in measurement. In science we account for this by using significant digits or significant figures
15. 15. The more significant digits in a measurement the more accurate the measuring device was.
16. 16. The more significant digits in a measurement the more accurate the measuring device was.
17. 17. The more significant digits in a measurement the more accurate the measuring device was.
18. 18. The number of significant digits tells us how accurate the measuring device was.
19. 19. Reporting calculations with the correct number of significant digits
20. 20. Reporting calculations with the correct number of significant digits Our calculations are only as precise as our least precise measurement.
21. 21. Our calculations are only as precise as our least precise measurement
22. 22. Our calculations are only as precise as our least precise measurement If 30 beans have a mass of 17.3g what is the average mass?
23. 23. Our calculations are only as precise as our least precise measurement If 30 beans have a mass of 17.3g what is the average mass? 17.3g/30 =
24. 24. Our calculations are only as precise as our least precise measurement If 30 beans have a mass of 17.3g what is the average mass? 17.3g/30 = 0.576666666666666666g
25. 25. Our calculations are only as precise as our least precise measurement If 30 beans have a mass of 17.3g what is the average mass? 17.3g/30 = 0.576666666666666666g Does it really make sense to claim such precision when we only measured out to one tenth of a gram?
26. 26. 17.3g/30 = 0.576666666666666666g The measurement has three significant digits
27. 27. 17.3g/30 = 0.576666666666666666g The measurement has three significant digits The measurement only has 3 significant digits so the answer should have only 3 significant digits.
28. 28. 17.3g/30 = 0.576666666666666666g The measurement has three significant digits The measurement only has 3 significant digits so the answer should have only 3 significant digits. 0.577g
29. 29. ROUNDING OFF RESULTS When performing a chain of calculations round off your answers only at the end. 13.44 round down 13.4 13.45 round up 13.5
30. 30. 3.1 Using and Expressing Measurements A measurement is a quantity that has both a number and a unit.
31. 31. Measuring with SI Units 5 of the 7 S.I. base units are used by chemists m meter (length) kg kilogram (mass) K kelvin (temperature) s second (time) mol mole (quantity)
32. 32. 3.2 Units and Quantities For very large or very small measurements, use a metric prefix.
33. 33. 3.2 Units and Quantities
34. 34. Units of Volume 3.2 Units and Quantities The SI unit of volume is the cubic meter (m)3, which is the amount of space occupied by a cube that is 1 m along each edge. A more convenient unit of volume for everyday use is the liter, a non-SI unit.
35. 35. Units of Volume 3.2 Units and Quantities The SI unit of volume is the cubic meter (m)3, which is the amount of space occupied by a cube that is 1 m along each edge. A more convenient unit of volume for everyday use is the liter, a non-SI unit. A liter (L) is the volume of a cube that is 10 centimeters (10 cm) along each edge. 10 cm × 10 cm × 10 cm = 1000 cm3 = 1 L
36. 36. 3.2 Units and Quantities Common metric units of volume include the liter, milliliter (aka cubic centimeter), and microliter.
37. 37. 3.2 Units and Quantities Common metric units of mass include kilogram, gram, milligram, and microgram.
38. 38. 3.2 Units and Quantities Scientists commonly use two equivalent units of temperature, the degree Celsius and the kelvin.
39. 39. Absolute zero = lowest possible temperature
40. 40. 3.2 Units and Quantities 1 C° = 1 K
41. 41. 3.2 Units and Quantities
42. 42. 3.2 Units and Quantities Energy is the capacity to do work or to produce heat.
43. 43. 3.2 Units and Quantities The joule (J) is the SI unit of energy. One calorie (cal) is the quantity of heat that raises the temperature of 1 g of pure water