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Measurement

Measurement. Common laboratory devices. In the chemistry laboratory, the balance is commonly used to measure mass. Central Carolina Scale. Metler Toledo PL Series Toploading Balances. Online. Available: http://mettler-toledo.centralcarolinascale.com/PL-Balance.htm. Accessed 28 June 2010.

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Measurement

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  1. Measurement

  2. Common laboratory devices

  3. In the chemistry laboratory, the balance is commonly used to measure mass Central Carolina Scale. Metler Toledo PL Series Toploading Balances. Online. Available: http://mettler-toledo.centralcarolinascale.com/PL-Balance.htm. Accessed 28 June 2010.

  4. In the chemistry laboratory, the ruler is commonly used to measure length Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  5. In the chemistry laboratory, the timepiece and stopwatch are commonly used to measure time Timex. Online. Available: http://www.timex.com/. Accessed 28 June 2010. Holabird Sports. Timex Marathon 50-Lap Stopwatch. Online. Available: http://www.holabirdsports.com/m/Running-Gear/Pedometers-Stopwatches/Timex/p1/870196.htm. Accessed 28 June 2010.

  6. In the chemistry laboratory, the thermometer is commonly used to measure temperature The Beer Keg. Online. Available: http://thebeerkeg.co.za/catalog/index.php?cPath=30. Accessed 28 June 2010.

  7. In the chemistry laboratory, different devices are used to measure volume Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

  8. What did the thermometer say to the graduated cylinder? You may have graduated, but I’ve got many degrees http://www.123rf.com/photo_3394414_thermometer--smiling-cartoon-illustration-as-vector.html http://27melody27.deviantart.com/art/Graduated-Cylinder-134411332

  9. Units

  10. Units are essential in stating measurements correctly Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill. Online. Available: http://www.mapcrow.info/cgi-bin/cities_distance_airpt2.cgi?city3=-3371735%2CQ&city4=9170030%2CT. Accessed 26 June 2010.

  11. The Cubit “length of the arm from the tip of the finger to the elbow” National Physical Laboratory. History of Length Measurement. Online. Available: http://www.npl.co.uk/educate-explore/posters/history-of-length-measurement/history-of-length-measurement-(poster). Accessed: 17 June, 2009.

  12. The Yard "the distance from the tip of the King's [King Henry I] nose to the end of his outstretched thumb" National Physical Laboratory. History of Length Measurement. Online. Available: http://www.npl.co.uk/educate-explore/posters/history-of-length-measurement/history-of-length-measurement-(poster). Accessed: 17 June, 2009.

  13. The SI system has seven base units from which all other units are derived Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  14. The temperature scales that are currently in use differ in the size of the unit and/or the zero point temperature Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  15. 0F = ( x 0C) + 32 5 0C = x (0F – 32) 9 9 5 It is possible to convert from one temperature scale to another Fahrenheit to Celsius Celsius to Fahrenheit Kelvin to Celsius K = 0C + 273.15 Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  16. Solder, an alloy made of tin and lead, is used in electronic circuits. A certain solder has a melting point of 224°C. What is its melting point in °F? Answer: 435°F Ebateable Blog. Solder On, Soldier! Online. Available: http://blog.ebates.com/ebates/2009/08/solder-on-soldier.html. Accessed 26 June 2010. Howard Electronic Instruments, Inc. No-Clean Solder Paste and NC Core Wire Solder. Online. Available: http://www.howardelectronics.com/amtech/nc500.html. Accessed 26 June 2010.

  17. SI units are modified in decimal fashion by a series of prefixes Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  18. Scientific notation

  19. To manage numbers more conveniently, scientific notation is used N x 10n For N, 1 ≤ N < 10 n = exponent = positive or negative whole number Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  20. If N < 1 or N ≥ 10, count the number of places that the decimal point must be moved to give the proper N • If the decimal point has to be moved to the left • add number of times from the original n • If the decimal point has to be moved to the right • subtract number of times from the original n Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  21. Convert the following into correct scientific notation • 20568 • Answer: 2.0568 x 104 • 0.2193 • Answer: 2.193 x 10-1 • 25 x 103 • Answer: 2.5 x 104 • 0.25 x 10-3 • Answer: 2.5 x 10-4

  22. How long is the metal strip shown below? Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  23. Significant figures

  24. The number of significant figures in a measurement depends on the measuring device Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  25. Rules of Significant Figures • Any non-zero digit is significant • Zeros between nonzero digits are significant • Zeros to the left of the first nonzero digit are not significant Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  26. Rules of Significant Figures • For numbers with a decimal point, zeros after the last non-zero digit are significant • For numbers without a decimal point, zeros after the last non-zero digit may or may not be significant • Scientific notation removes the ambiguity • Counting numbers and conversion factors have unlimited number of significant figures Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  27. How many significant figures does each quantity have? • 5.35 g • Answer: 3 sf • 3.80 moles • Answer: 3 sf • 607 K • 3 sf

  28. How many significant figures does each quantity have? • 0.0080 L • 2 sf • 26 letters in the English alphabet • Unlimited number of sf • 1 km = 1000 m • Unlimited number of sf

  29. In rounding off numbers, look at the leftmost digit to be dropped • If the leftmost digit to be removed is less than 5, the preceding number is left unchanged • If the leftmost digit to be removed is 5 or greater, the preceding number is increased by 1 Example: 7.248 g Rounded to two significant figures: 7.2 g Rounded to three significant figures: 7.25 g

  30. 83.5 mL + 23.28 mL 865.9 mL - 2.8121 mL Rules for significant figures in answers 1. For addition and subtraction. The answer has the same number of decimal places as there are in the measurement with the fewest decimal places. Example: adding two volumes 106.78 mL = 106.8 mL Example: subtracting two volumes 863.0879 mL = 863.1 mL Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  31. Rules for significant figures in answers 2. For multiplication and division. The answer contains the same number of significant figures as there are in the measurement with the fewest significant figures. Example: multiplying numbers = 23.4225 cm3 =23cm3 9.2 cm x 6.8 cm x 0.3744 cm Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  32. Rules for significant figures in answers • Counting numbers and conversion factors have unlimited number of significant figures • For multiple-step problems, carry on some insignificant numbers

  33. 1 g 16.3521 cm2 - 1.448 cm2 1000 mg (a) 7.085 cm 4.80 x104 mg x (b) 11.55 cm3 Perform the following calculations and express the final answer with the correct number of significant figures Answer: 2.104 cm Answer: 4.16 g/cm3

  34. Terms used in discussing uncertainties

  35. Precision is a measure of how closelyindividual measurements agreewith one another Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

  36. Accuracy refers to how closely individual measurements agree with the correct, or “true” value Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

  37. Factor-label method

  38. 1 peso = 1 4 25-centavos unit factor 4 25-centavos = 1 1 peso The factor-label method is used to convert from one unit to another 1 peso = 4 25-centavos Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  39. SI units are modified in decimal fashion by a series of prefixes Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  40. Perform the following calculations and express the final answer with the correct number of significant figures • 234 pesos to 25-centavos • Answer: 936 25-centavos • 57.8 m to cm • Answer: 5.78 x 103 cm • The density of silver is 10.5 g/cm3. Convert the density to units of kg/m3. • Answer: 1.05 x 104 kg/m3

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