WARMUP (10 minutes) 5.00/98.000 (19.5)(2) 34.9/0.39 For each problem: Identify the number of significant figures in each value Perform the operation Round your answer to the correct number of sig figs, and report your answer twice: using scientific notation and regular notation 5.00/98.000 (19.5)(2) 34.9/0.39 4. (7.5 x 10-3)(9.36 x 10-4) 5. 8.21 x 103/9.12 x10-5 = 0.0510 or 5.10 x 10-2 = 40 or 4 x 101 = 89 or 8.9 x 101 = 0.0000070 or 7.0 x 10-6 = 90021929.82 so 90000000 or 9.00 x 107

Quantitative Chemistry continued… Bring 4 beverages per lab group 2 classes from now. That’s like 1 per person. Make sure they are different. No diet drinks.

Three Temperature Scales Formulas: °F = (1.8)(°C) + 32 K = °C + 273 °F ← °C → K 25 °C 77⁰F 298K

Liquid hydrogen boils at -179.13 Celsius. What is this in Kelvin? K = °C + 273 K = -179.13 + 273 = 93.87 K using sig figs from problem = 94 K ”adding” sig figs The melting point of uranium hexafluoride is 139.8⁰F.  What is the melting point of uranium hexafluoride on the Celsius scale? °F = (1.8)(°C) + 32 °C = (°F – 32)/1.8 °C = 59.88888 = 59.89°C

We want measurements that are both precise and accurate Precision: size of the unit you use to make the measurement. Accuracy : difference from the accepted correct answer. Can you can make a measurement that's very precise, but not very accurate? 9-volt battery  you measure as 17.1453 volts. You must have used a device that allowed 4 decimal places of precision, but your answer was inaccurate! Your highly precise answer was not very accurate, was it? Can a number be accurate, but not very precise? 451 ml can of soup  you measure it as 450 ml. Neither value is very precise, but your measurement is reasonably accurate

a. Which student was the MOST accurate? Four students measured the volume of a liquid. Each student measured the liquid 3 times. The actual volume of the liquid is 22.3 mL. a. Which student was the MOST accurate? b. Which student was the LEAST accurate? c. Which student was the MOST precise? d. Which student was the LEAST precise? Student Trial 1 Trial 2 Trial 3 Average Student A 25.0 mL Student B 24 mL 23 mL 22 mL Student C 12 mL 27 mL 15 mL 18.0 mL Student D 20 mL

Measure THIS! 3.0 ml 5.75 ml 0.34 ml How should the volume be recorded for each instrument? What is the uncertainty for each instrument? + 0.1 ml + 0.01 ml + 0.01 ml

How should volume be recorded in this 100 ml beaker? 40.0 ml? 40ml? 40. ± 1ml Technically, it’s ± 2 ml for this beaker but I don’t want to get to detailed about uncertainty. The point is: how precise are you ALLOWED to be? How should volume be recorded if the water level were HERE, right on the calibration mark?? 80.0? 79? 79.0? 81? 80. ± 1ml 80 ml 60 ml 40 ml 20 ml

Measure THIS Don’t forget to estimate one decimal point past how the instrument is calibrated!