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## Unit 2

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**Unit 2**Chapter 3 Scientific Measurement**Today…**• Turn in: • Fill out Goal Sheet and turn in (enter scores and calculate grade) • Our Plan: • Elements Song • Review – Quiz, Quiz Trade • Symbols Quiz • New Calendar/Goal Sheet • Notes – Scientific Notation, Accuracy, Precision, Percent Error • Worksheet #1 • Wrap Up: Online Quiz • Homework (Write in Planner): • Complete WS #1 by next class • 2nd Symbols Quiz Next Time**Element Song**http://www.youtube.com/watch?v=GFIvXVMbII0**Ready for the Symbols Quiz?**Magnesium Aluminum Zinc Gold Phosphorus Carbon Francium Calcium Boron Lithium Iron Mg • Fe • Ag • H • He • O • Ar • K • Xe • I • U Silver Al Hydrogen Zn Au Helium Oxygen P C Argon Fr Potassium Ca Xenon Iodine B Li Uranium**Challenge**• This text message is too long. In the space provided in your notebooklet, write it as short as possible, but make sure it still has the same meaning… • Hello Mrs. Chamberlain, I need your help! I do not know what time school starts tomorrow. Thank you.**Challenge**• The number 602200000000000000000000 is used so frequently in chemistry that it has its own name; Avogadro’s number. What would be a better way of writing it?**Scientific Notation**• To write a number in scientific notation: • Move the decimal so that the number is between 1 and 10. • The exponent is the number of tens places you moved the decimal • Moving the decimal right = - exponent Moving the decimal left = + exponent**Examples**• 65000 m = • 0.0000156 s = • 0.24 m/s = • 6.7 mm = 6.5 x 104 m 1.56 x 10-5 s 2.4 x 10-1 m/s 6.7 x 100 mm**To Write a number in Standard Form**• Change it from scientific notation to a standard number by moving the decimal. • Example 1.4 x 106 = 1,400,000 2.6 x 10-4 = 0.00026**Adding & Subtracting**• Change the numbers to the same exponent. • Add or subtract the numbers • Example: 4.1 x 106 + 8.5 x 107 • 0.41 x 107 + 8.5 x 107 = 8.91 x 107**Multiplication**• Multiply the numbers • Add the exponents • Example: (4 x 106)(2 x 108) • 8 x 1014**Division**• Divide the numbers • Subtract the exponents • Example: (9 x 107)/(3 x 104) • 3 x 103**Try It Out!**• 3.5 x 104 + 5.1 x 105 • (5.7 x 108)(3.5 x 106) • (6.9 x 106)/(4.5 x 103)**Answers**• 5.45 x 105 • 1.995 x 1015 • 1.53 x 103**Or…**• Use your scientific calculator. • The EE button means x10^ • Do the Try it Out problems again using your calculator and see if you get the correct answers!**Accuracy & Precision**• Accuracy – a measure of how close a measured value is to the actual value • Example: If a weight is labeled 5 g and a balance reads 5 g when you place it on it, the balance is accurate.**Accuracy & Precision**• Precision – a measure of the reproducibility of a measurement. • It is how close a series of measurements are to one another. • Example – If I find the mass of a 5g weight on a balance 3 times and I get 4.99g each time it is precise.**Accuracy & Precision**• High precision is denoted by a large number of significant figures (decimal places). • Typically, high quality instruments measure things with high precision and accuracy. • That’s why a lab balance costs $300 + and your bathroom scaled costs $8.**Accurate, Precise, Both, Neither?**Accurate**Accurate, Precise, Both, Neither?**Accurate**Percent Error**Percent Error = |experimental - actual| actual value • The absolute value is present so that percent error is always POSITIVE! X 100**Example**• Working in the laboratory, a student finds the density of a piece of pure aluminum to be 2.85 g/cm3. The accepted value for the density of aluminum is 2.699 g/cm3. What is the student's percent error? Percent Error = |2.85 – 2.699| 2.699 5.59% X 100 =**Try It Out**• A student takes an object with an accepted mass of 200.00 grams and masses it on his own balance. He records the mass of the object as 196.5 g. What is his percent error? Percent Error = |196.5 – 200.00| 200.00 1.75% X 100 =**STOP!**• Complete Worksheet #1 by next class • Worksheets are… • A completion grade (i.e. You do not get a grade until it is 100% finished) • 10 points at beginning of class • 9 points late on due date • -2.5 points each day it’s late**Wrap Up**• Online Scientific Notation Quiz - http://www.sciencegeek.net/Activities/scientificnotation.html • Get Mrs. C’s signature on your Worksheet after you complete 15 correctly.**Today…**• Turn in: • Get out WS#1 to Check • Fill out Bingo Card with any symbols • Our Plan: • Symbols Review – Bingo • Symbols Quiz #2 • Scientific Notation Clicker Review • Scientific Notation Quiz • Notes – Significant Figures/Units of Measurement • WS #2 • Bluff • Homework (Write in Planner): • Complete WS #2 by next class (9/12) • QUIZ OVER SIG FIGS NEXT TIME!**Even toddlers learn their element symbols…**• http://www.youtube.com/watch?v=z_6u1njmX8g**Intro to Units & Sig Figs**• http://www.youtube.com/watch?v=hQpQ0hxVNTg&feature=share&list=UUX6b17PVsYBQ0ip5gyeme-Q**Units in Chemistry**• When you add or subtract two numbers, they must have the same units. • The answer then has those units as well. • Example: 4 m + 12 m = 16 m**Units in Chemistry**• When you multiply, you also multiply the units. • Examples: • 4 m x 5 m = 20 m2 • 2 g x 3 s = 6g·s • When you divide, you also divide the units. • Examples: • 4 m / 2 s = 2 m/s • 8 g / 2 mL = 4g/mL**Challenge!**• What does the word “significant” mean?**Significant Figures**• The numbers that are known, plus a digit that is estimated**Why do we need significant figures?**• Because we live in the real world! • Although we can imagine finding a measurement to perfect accuracy with some hypothetical instrument, we never actually do because real instruments aren’t infinitely accurate. • Because our instruments aren’t perfect, it’s important that we somehow indicate how good our instruments are to anybody looking at our data. • We do this by limiting the number of digits we write in a measured number to the significant figures.**An example…**• If I told you that I weigh 80.6388154 kilograms, you’d probably assume that I gave you all of those numbers after the decimal place because I weighed myself on a special scale that can measure to that precision. • You wouldn’t assume that I used my bathroom scale, because it would never give you a reading with that many digits (it’s not that precise).**RULES*****All nonzero numbers are significant*** 125, 689 has 6 significant figures (sig figs) 156 has 3 sig figs • Zeros between nonzero numbers are significant. • 40.7 mL has ______ sig figs • 870,009 g has _____ sig figs 3 6**RULES**• Zeros in front of nonzero numbers are not significant • 0.00011 s has _____ sig figs • 0.956 g/mL has _____ sig figs 2 3**RULES**• Zeros at the end of a number and to the right of a decimal are significant • 85.0000 kg has _____ sig figs • 2.00000000 L has _____ sig figs 6 9**RULES**• Zeros at the end of a number are NOT significant. If there is a decimal at the end, they ARE. • 2000. m/s has _____ sig figs • 2000 m/s has _____ sig figs 4 1**EASY RULE!**Memorize! Start at the first nonzero number on the left and count every number right Start at the first nonzero number on the right and count every number left**Unlimited Significant Figures**• Counting – There are 23 students in the classroom • Could also be expressed as 23.0 or 23.00000000000000 etc. • Conversion Factors – 60 min = 1 hour • Exact quantities do not affect the process of rounding**Try It Out**• How many sig figs? • 0.00125 • 1.12598000 • 3,000 • 0.0100103 • 5,500. • 1.23 x 105 3 9 1 6 4 3**Rounding Tips**• When rounding a large number, consider it in terms of owing someone money. • If I owed you $4567 and I want to round that to 1 significant figure, you would not want me to round it to $5. • The correct way to round it would be $5000. • And remember, a 5 or larger after the place/digit you are rounding to means that you round up.**Rounding**• Round the following numbers so that they have 3 significant figures: • 1.36579 = • 120 = • 145,256,987 = • 0.0001489651 = 1.37 1.20 x 102 OR 120. 145,000,000 0.000149**To Multiply & Divide Sig Figs…**• Count the number of sig figs in each number • Round the answer so that it has the same number of sig figs as the number in the problem with the fewest.