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## Unit 2

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**Bell work**• Turn in Unit 2 preview. What pieces of laboratory equipment are you familiar with? What are they used for or what do they measure?**Agenda**• Bell work • Scientific discovery lab • Textbook overview**Measurement lab edits**• Station 1 – Write what each line represents. • Station 2 • You will be using pipettes, but it’s a different type of pipette than described in the lab. There is no wheel or anything, you just squeeze the bulb. • Station 6 • Ignore the page numbers. Just look through chapter 2 for the answers.**Textbook questions**• If you finish early, grab a textbook from the shelf and peruse chapter 2. • What is the SI system? What is a base unit? What is a derived unit? • Copy the first 5 rows of table 2.1 into your notes • Copy all of table 2.2 into your notes**Bell work**• Turn in measurement lab. • What is the volume in each of these (mL): 70 50 60 60 40 40 50 30 20**Agenda**• Bell work • Scientific notation overview • SI Prefixes and metric to metric conversions • Homework: Metric to metric conversions**Scientific notation**• Used to express numbers that are really big or really small • Move the decimal place • (+) : move decimal place to the right • Make number bigger • (-) : move decimal place to the left • Make number smaller**Scientific notation examples**• Express the following in scientific notation: 51,200,000 3640 0.00432 • Express the following in standard notation: 7.6 x 10-4 8.98 x 103 5.321 x 10-6**Scientific notation practice**• Express the following in scientific notation: 72,000 0.0129 0.000056 • Express the following in standard notation: 9.10 x 105 4.33 x 10 -5 8.01 x 103**Adding and subtracting**• You need to have the same power of ten, so adjust one to match the other • Then add or subtract the numbers • Give answer in scientific notation • 2 × 103 + 3.6 × 104 • 0.2 x 104 + 3.6 x 104 • (0.2 + 3.6) x 104 • 3.8 x 104**Example**• 7 × 105 – 5.2 × 104 • 70 x 104 – 5.2 x 104 • (70-5.2) x 104 • 64.8 x 104 • 6.48 x 105**Multiplying and dividing**• Multiply decimal numbers • For multiplying, add exponents on powers of 10 • For dividing, subtract exponents on powers of 10 • (2.6 x 107) (6.3 x 104 ) • (2.6 x 6.3) = 16.38 • 107 x 104 = 1011 • 16.38 x 1011 • 1.638 x 1012**Example**• (2 x 108) (3.2 x 105) • 2 x 3.2 = 6.4 • 108 + 105 = 1013 • 6.4 x 1013**Dividing**• Divide decimal numbers • Subtract exponents on powers of 10 • (2.4 x 1011) / (1.2 x 104) • 2.4 / 1.2 = 2 • 1011 / 104 = 107 • 2 x 107**Example**• (5.76 x 109) / (3.2 x 103) • 5.76 / 3.2 = 1.8 • 109 / 103 = 106 • 1.8 x 106**Measurement**• Base units – basic units of measure • Ex: • Derived units – formed from a combination of base units • Ex: • Metric vs English • 1 in = 0.0254 m or 2.54 cm • 1 ft = 0.3048 m • 1 mi = 1.61 km or 1609 m • 1.8°F = 1°C • 1 Gal = 0.003785 m3 • 2.2 lb = 1 kg**Table 2.1**• SI Base units – there are 7 but we’re concentrating on 5 • SI (SystemeInternacionale) • Internationally standardized measurement notation • Copy this table into your notes**Table 2.2**• SI Prefixes – added to base units • Copy this table into your notes**Metric to Metric Conversions**• All you’re doing is moving the decimal point • You need to think about what the prefix means (10whatever) and if you’re going from a bigger unit to a smaller unit or vice versa • Small big ; your number should be smaller 10 cm = ________ m • Big small; your number should be bigger 5 L = ______ dL**Practice**• Use the table of SI prefixes to complete the following metric to metric conversions • h = hecto; means 102 • This will be your homework**Bell work**• Turn your metric to metric conversions practice into the tray. • What is the length shown on each of these (cm): 5 70 6 4 60 4 3 50 2**Agenda**• Overview of measurement lab • Precision vs accuracy • Precision vs accuracy lab • Dimensional analysis • Exit ticket: scientific notation practice • Homework: Precision vs accuracy lab 4 problems at end of this lecture**Measurement lab**• Station 1 • What we’ve been doing in the bell work • What volume does each line on the equipment measure? 30 125 3 6 80 100 60 20 2 4 40 10 50 1 2 20 75**Station 1**• What did you notice when you measured 100 mL with the Erlenmeyer flask and beaker? • If you wanted 100 mL exactly, which piece of glassware would you use?**Station 2**• Which most accurately measured 10 mL of water: pipette or beaker? • Which piece of glassware would be best to use when measuring small quantities of liquid?**Station 3**• Uncertain digit • Meter sticks on paper – bottom is more precise (has more decimal places) and has less uncertainty • Table dimensions in meter • Table dimensions in centimeters • Volume of table**Station 4**• We’ve done some practice with reading volumes during bell work • Any questions on that? • When would you NOT want to use the most precise graduated cylinder?**Station 5**• Mass of rubber stopper, 150 mL beaker, and watch glass • What decimal place is the estimated place for our balances?**Percent Error**• Used to evaluate accuracy • % error = (error / accepted value) x 100 • Error = experimental value – actual value (should always be positive so take absolute value) • Smaller % error is more accurate • % accuracy = experimental / accepted x 100 • Greater % accuracy is more accurate**Percent Error**• % error + % accuracy = 100 • 22.) 5.45 % • 23.) 7.27% • 24.) You did because you have a lower % error, which means your value was closer to the accepted value.**Station 6**• Quantitative vs qualitative • Precise measurement – more decimal places in measurement, more precise • Precision vs accuracy**Precision vs accuracy**• Precision: repeatable, several measurements close together • Accuracy: close to the accepted value**Accuracy**How close you are to the accepted value. Good Accuracy**Accuracy**How close you are to the accepted value. Bad Accuracy**Precision**How close you are to repeating a result. Good Precision**Precision**How close you are to repeating a result. Bad Precision**Good Precision and Accuracy**You want both: repeatedly getting a result close to the accepted or desired value. Good Accuracy and Precision**Precision vs Accuracy lab**• Read through the lab • Everyone is going to get a chance to see how precise/accurate they are • Same lab groups as before**Dimensional analysis**• Converting by cancelling units • Steps • Write down what you are given • Find the appropriate conversion factors • Figure out what goes on top and what goes on the bottom • What you want to cancel goes on the bottom • What you want goes on the top • Multiply across the top and divide by what’s on the bottom • 10 hL = ____ L 5 mi = ______ ft 15 km = ______ in**Dimensional analysis practice**• Try the following conversions using the dimensional analysis method: 15 s = _______ min 7 m = ______ mi 30° C = _____ K 63 in = ________ dm**Bell work**• Turn in your precision vs accuracy lab. Pull out the 4 dimensional analysis problems I asked you to try from last class. • The accepted mass of a rock is 20.1 g. Jon used a balance and found the mass to be 18.3 g. Jeff found the mass to be 21.3 g. Find both Jon and Jeff’s percent error. Whose balance was more accurate?**Agenda**• Bell work • Review 4 dimensional analysis problems • Significant figures • Whiteboard practice • Cut and paste dimensional analysis lab • Homework: Cut and paste dimensional analysis lab**Dimensional analysis practice**• Try the following conversions using the dimensional analysis method: 15 s = _______ min 7 m = ______ mi 30° C = _____ K 63 in = ________ dm**All nonzeronumbers aresignificant**7 km has one sig. fig. 55 km/s has two sig. figs. 11,257 kg has five sig. figs.**Zeros between nonzero numbers are significant**703 J has three sig. figs. 7.03 V has three sig. figs. 7003 kg has four sig. figs.**Zeros in front of nonzero digits are not significant**0.753 m/s has three sig. figs. 0.00753 N has three sig. figs.