1 Chapter 3: Temperature, Proportions, Density, Problem Solving Sections Chemistry 111

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3 Topics Probably won’t Finish Chapter 3 Today –1 st set of workbook problems will be due Thursday 7/8 (you should have started them already) Significant Figures Temperature Lecture Temperature Exercise Problem Solving: –Identify Knowns & Unknowns –Per Paths

4 Chapter 3 - Exercise #1 (Recap) How many  m are there in 2 miles? a.miles  km  m   m b.miles  ft  in  cm  m   m To Solve: (1)Find all of your conversion ratios (PERs) & write them out (one for each arrow). (2)Start with the given & write out the problem. (3)Punch in the numbers.

5 Chapter 3 - Exercise #1 (Recap) miles  km  m   m

6 Chapter 3 - Exercise #1 (Recap) miles  ft  in  cm  m   m

7 Counting Significant Figures 1.Nonzero Integers. Nonzero integers always count as significant figures. 2.Zeros. There are three classes of zeros: 1.Leading Zeros are zeros that precede all the nonzero digits. These do not count as significant figures. In the number , the three zeros simply indicate the position of the decimal point. This number has only two significant figures. 2.Captive Zeros are zeros between nonzero digits, these always count as significant figures. The number has four significant figures. 3.Trailing Zeros are zeros at the right end of the number. They are significant only if the number contains a decimal point.

8 Counting Significant Figures Note 1:In Scientific notation, all digits in the coefficient are significant figures. Note 2:Exact numbers can be considered to have a  (infinite) number of significant figures.

9 Rules for Computations & Sig. Figs. 1.For multiplication and division, the number of significant figures in the result is the same as the number with the least precise measurement used in the calculation. For example: × 4.1 =  24 2.For addition and subtraction, the result has the same number of decimal places as the least precise measurement used in the calculation. Set the problem up like 2 nd grade math!  28.4

10 Rules for Computations & Sig. Figs. Note 1:For multiplication and division – the sig. figures are counted. Note 2:For addition and subtraction – the decimal places are counted.

11 Temperature Scales Fahrenheit (°F) Celcius (°C) Kelvin (K) U.S. Weather Chem. Lab, Metric Weather Science Lab, especially gases.

12 RATIO OF STEPS IS EXACTLY: ——— = ——— = — Fahrenheit & Celcius FahrenheitCelcius 32° Freeze 0° Lotsa Steps (180) Nice # of steps (100) 212° Boil 100°

13 Kelvin Same scale as Celcius Never use the degree symbol ° Starts at Absolute Zero –0.0 K = absolute zero – K = 0.0 °C –All molecular motion is stopped at absolute zero.

14 Team Exercise #1 – Sample Fahrenheit (°F)Celcius (°C)Kelvin (K)Why it’s Important

15 Team Exercise #1 – 20 Minutes Develop a table of your favorite / important temperatures. Determine the temperature (with sig. figs.) in °C, °F, and K at each of these temperatures. –Chemically important: 25 °C, 0.0 K, 77.3 K –Life important: 98.6 °F, 32 °C, 451 °F, 107 °F –Your favorite: ________, _______, _______ Don’t forget: –Do one sheet of paper. –Put everyone’s name on it. –Fill in your log sheet.

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17 Writing PER/PATHS This needs practice! I’ll do a few, you’ll do a few.

18 Writing PER/PATHS (2) A woman gives birth to a 7.5-lb baby. How would a hospital using metric units record this baby’s mass? Start: lb End: kg Path: lb – oz – g – kg Conversions:

19 Writing PER/PATHS (3) How many grams of milk are in a 12.0 fluid-ounce glass? Start: fl.oz. End: g Path: fl.oz.– qt – gal – ft 3 – lb – g Conversions:

20 Writing PER/PATHS (4) Standard typewriter paper in the United States is 8½ in. x 11 in. What is the area in centimeters? Start: in End: cm 2 Path: in  in 2 – cm 2 Conversion:

21 Team Work #2 Work on book homework as a team BUT… –Follow the organization in Figure 3.9. –Work as a team on 1 sheet of paper & turn it in at the end of class. –Full credit Points for getting at least 2 done. –Use 1 sheet of paper for each problem. Do these (from book HW assignment): –28, 31, 35, 50