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Learning Check

Learning Check. What is the length of the wooden stick? 1) 4.5 cm 2) 4.58 cm 3) 4.584 cm. Measurement and Significant Figures. Every experimental measurement has a degree of uncertainty. The volume, V, at right is certain in the 10 ’ s place, 10mL<V<20mL

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Learning Check

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  1. Learning Check What is the length of the wooden stick? 1) 4.5 cm 2) 4.58 cm 3) 4.584 cm

  2. Chapter Two Measurement and Significant Figures • Every experimental measurement has a degree of uncertainty. • The volume, V, at right is certain in the 10’s place, 10mL<V<20mL • The 1’s digit is also certain, 17mL<V<18mL • A best guess is needed for the tenths place. 17.6 ML

  3. www.chrisjordan.com

  4. 106,000 aluminum cans, the number used in the US every 30 seconds. www.chrisjordan.com

  5. How many cans are used in a year? www.chrisjordan.com

  6. Scientific Notation • # from 1 to 9.999 x 10exponent • 800 = 8 x 10 x 10 • = 8 x 102 • 2531 = 2.531 x 10 x 10 x 10 • = 2.531 x 103 • 0.0014 = 1.4 ÷ 10 ÷ 10 ÷ 10 • = 1.4 x 10-3

  7. Change to standard form. • 1.87 x 10–5 = • 3.7 x 108 = • 7.88 x 101 = • 2.164 x 10–2 = 0.0000187 370,000,000 78.8 0.02164

  8. Change to scientific notation. • 12,340 = • 0.369 = • 0.008 = • 1,000. = 1.234 x 104 3.69 x 10–1 8 x 10–3 1.000 x 109

  9. No Cussing! The following 4-Letter words are forbidden here: Inch Mile Foot Pint Yard Acre And we never swear the BIG F (useoC) Please keep it clean and Metric

  10. SI System • The International System of Units • Derived Units Commonly Used in Chemistry Map of the world where red represents countries whichdo not use the metric system

  11. The International System of Units • Length meter m • Mass kilogram kg • Time second s • Amount of substance mole mol • Temperature Kelvin K • Electric current amperes amps • Luminous intensity candela cd Quantity Name Symbol Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 16

  12. NEED TO KNOW Prefixes in the SI System Power of 10 for Prefix Symbol Meaning Scientific Notation _________________________________________________________ mega- M 1,000,000 106 kilo- k 1,000 103 deci- d 0.1 10-1 centi- c 0.01 10-2 milli- m 0.001 10-3 micro-m 0.000001 10-6 nano- n 0.000000001 10-9

  13. Certain Digits Uncertain Digit Significant figures • Method used to express accuracy and precision. • You can’t report numbers better than the method used to measure them. • 67.20 cm = four significant figures ???

  14. Significant figures • The number of significant digits is independent of the decimal point. • 255 • 31.7 • 5.60 • 0.934 • 0.0150 These numbers All have three significant figures!

  15. Rules for Counting Significant figures • Every non-zero digit is ALWAYS significant! • Zeros are what will give you a headache! • They are used/misused all of the time. • SEE p.24 in your book!

  16. 4,008 - four significant figures 0.421 - three significant figures Leading zero Captive zeros 114.20 - five significant figures Trailing zero Rules for zeros ??? • Leading zeros are notsignificant. • Captive zeros are always significant! ??? Trailing zeros are significant … IF there’s a decimal point in the number! ???

  17. Examples • 250 mg • \__ 2 significant figures • 120. km • \__ 3 significant figures • 0.00230 kg • \__ 3 significant figures • 23,600.01 s • \__ 7 significant figures

  18. Significant figures:Rules for zeros • Scientific notation - can be used to clearly express significant figures. • A properly written number in scientific notation always has the proper number of significant figures. 0.00321 = 3.21 x 10-3 Three Significant Figures

  19. Significant figures and calculations • An answer can’t have more significant figures than the quantities used to produce it. • Example • How fast did you run if you • went 1.0 km in 3.0 minutes? 0.333333 speed = 1.0 km 3.0 min = 0.33 km min

  20. ONLY 3 SIG FIGS! ONLY 2 SIG FIGS! Significant figures and calculations • Multiplication and division. • Your answer should have the same number of sig figs as the original number with the smallest number of significant figures. 21.4 cm x 3.095768 cm = 66.2 cm2 135 km ÷ 2.0 hr = 68 km/hr

  21. 123.45987 g + 234.11 g 357.57 g 805.4 g - 721.67912 g 83.7 g Significant figures and calculations • Addition and subtraction • Your answer should have the same number of digits to the right of the decimal point as the number having the fewest to start with.

  22. Rounding off numbers • After calculations, you may need to round off. • If the first insignificant digit is 5 or more, you round up • If the first insignificant digit is 4 or less, you round down.

  23. Examples of rounding off If a set of calculations gave you the following numbers and you knew each was supposed to have four significant figures then - 2.5795035 becomes 2.580 34.204221 becomes 34.20 1st insignificant digit

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