Chemistry – Sept 6, 2018 P3 Challenge – 1. How many sig figs do each of these contain? A) 3.80 x 108 B) 4700 C) 0.001090 2. Perform the following operations and round to the proper number of sigfigs. A) 9.866 m x 13.5 m B) 9.866 m – 13.5 m Get out Metric Conversions Homework for check

Objectives, Agenda, Assignment The factor label method (dimensional analysis) Agenda Homework Review The Factor Label Method One step conversions Multi-step conversions (time permitting) Ratio conversions Square conversions What’s Due? Complete the Factor Label Conversions Worksheet What’s Next? Read the Lab Report Format posted online

Metric WS Ans 1. a) 1.20 cm b) 0.2485 L c) 0.101 kg d) 0.035 m2 e) 970 m f) 1,580,000 mg g) 0.000183 km h) 6200 μs 2. a) 5.48 x 10-3 nm b) 13 L c) 3.17 x 10-2 m2 d) 1.92 x 106 mm2 e) 7.79 μm 3. a) 6.51 m b) 7,835 g

Metric WS Ans 4. a) 2.77 m b) 620 m c) 3,857,000 mg d) 3.40 x 102 g or 340. g e)2.3 x 10-2 L or 0.023 L f) 1.275 x 104 km or 12,750 km g) 0.078 mL h) 3.4 x 102 ms or 340 ms i) 3 x 102 Mm or 300 Mm j) 3.6 μL k) 0.856 kg l) 8.06 x 10-6 mm m) 81.05 m2

Unit Conversions (Factor-Label method) Write the measured value with its unit. (Given) Draw the multiplication symbol and a division line. Copy the unit to the bottom of the conversion factor to cancel. “Times sign, draw a line, copy the unit” Write the target unit on the top of the conversion factor. Find an equivalence using these two units and complete the conversion factor. Multiply and cancel units. (Multiply by tops, divide by bottoms) Report value with the target unit. (Use correct sigfigs)

Unit Conversions (Factor-Label method) How do you use conversion factors? Focus on the method here. Ex: How many minutes are there in 24 hours? 60 min 24 hours = 1440 min 1 hour Valid process because all conversion factors = 1. Ex: 6.35 Gm  m Ex: How many days are there in a 3.5 weeks? Ex: 4.11 mm  cm

Meter Stick Equivalences Three equivalences are used often in conversion factors They are called the meter stick equivalences because they all relate to the meter stick Easy to visualize and remember. Also works for other base units: 1000 mL = 1 L 1 m = 100 cm 1 m = 1000 mm 1000 m = 1 km

Unit Conversions (Factor-Label method) “Times sign, draw the line, copy the unit.” Variations on the theme Multistep conversions Squared unit conversions Ratio unit conversions

Multistep conversions “Times sign, draw the line, copy the unit.” If you do not know of the equivalence between the measured unit, and the target unit, consider a third unit that has an equivalence with both. Ex: convert 4.75 km to cm (remember sigfgs) km m cm 1000 m 100 cm 4.75 km = 475000 cm 1 km 1 m = 4.75 x 105 cm

Squared unit conversions If a unit is raised to a power, often 2 or 3, to perform a conversion, you must raise the entire conversion factor to that power. Convert 22 cm2 to m2 2 1 m 22 cm2 = 0.0022 m2 = 2.2 x 10-3 m2 100 cm

Ratio unit conversions Many derived units involve ratios of units. km/hr, m/s2… If a unit on the bottom needs to be converted, “copy the unit” to the top. Ex: Convert 25 m/s to km/h meter km s min hr 25 m 1 km 60 s 60 min = 90. km/hr 1 s 1000 m 1 min 1 hr

Exit Slip - Homework Use the factor label method to convert 45 km to m. What’s Due? (Pending assignments to complete.) #3 on Metric converstion WS Factor Label Conversions Worksheet, front side only. What’s Next? (How to prepare for the next day) Read the Lab Report Format posted online