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I II III Units of Measurement CH. 2 - MEASUREMENT.

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Presentation on theme: "I II III Units of Measurement CH. 2 - MEASUREMENT."— Presentation transcript:

1 I II III Units of Measurement CH. 2 - MEASUREMENT

2 A. Number vs. Quantity Quantity - number + unit UNITS MATTER!!

3 I II III II. Using Measurements CH. 2 - MEASUREMENT

4 A. Accuracy vs. Precision Accuracy - how close a measurement is to the accepted value Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

5 A. Accuracy vs. Precision

6 B. Percent Error Indicates accuracy of a measurement your value given value

7 B. Percent Error A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. % error = 2.9 %

8 C. Significant Figures Indicate precision of a measurement. Recording Sig Figs Sig figs in a measurement include the known digits plus a final estimated digit 2.31 cm

9 C. Significant Figures Counting Sig Figs Digits from 1-9 are always significant. Zeros between two other sig figs are always significant One or more additional zeros to the right of both the decimal place and another sig digit are significant Count all numbers EXCEPT: Leading zeros Trailing zeros without a decimal point -- 2,

10 , C. Significant Figures Counting Sig Fig Examples , sig figs 3 sig figs 2 sig figs

11 C. Significant Figures Calculating with Sig Figs Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm 3 )(23.3cm 3 ) = g 324 g 4 SF3 SF

12 C. Significant Figures Calculating with Sig Figs (cont) Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer mL mL 7.85 mL 224 g g 354 g 7.9 mL 350 g 3.75 mL mL 7.85 mL 224 g g 354 g

13 C. Significant Figures Calculating with Sig Figs (cont) Exact Numbers do not limit the # of sig figs in the answer. Counting numbers: 12 students Exact conversions: 1 m = 100 cm 1 in any conversion: 1 in = 2.54 cm

14 C. Significant Figures 5. (15.30 g) ÷ (6.4 mL) Practice Problems = g/mL 18.1 g g g g 4 SF2 SF 2.4 g/mL 2 SF

15 D. Scientific Notation A way to express any number as a number between 1 and 10 (coefficient) multiplied by 10 raised to a power (exponent) Number of carbon atoms in the Hope diamond 460,000,000,000,000,000,000, x Mass of one carbon atom g 2 x g coefficient exponent

16 D. Scientific Notation Converting into Sci. Notation: Move decimal until theres 1 digit to its left. Places moved = exponent. Large # (>1) positive exponent Small # (<1) negative exponent Only include sig figs. 65,000 kg 6.5 × 10 4 kg

17 D. Scientific Notation 7. 2,400,000 g kg km mm Practice Problems g kg km 62,000 mm

18 D. Scientific Notation Calculating with Sci. Notation (5.44 × 10 7 g) ÷ (8.1 × 10 4 mol) = 5.44 EXP EE ÷ ÷ EXP EE ENTER EXE = = 670 g/mol= 6.7 × 10 2 g/mol Type on your calculator:

19 D. Scientific Notation 11. (4 x 10 2 cm) x (1 x 10 8 cm) 12. (2.1 x kg) x (3.3 x 10 2 kg) 13. (6.25 x 10 2 ) ÷ (5.5 x 10 8 ) 14. (8.15 x 10 4 ) ÷ (4.39 x 10 1 ) 15. (6.02 x ) ÷ (1.201 x 10 1 ) Practice Problems cm kg x x x 10 22

20 Chemistry Binder Organization Chemistry Binder: (8 tabs) Reference: Administrative papers (policies & procedures, etc) Chemistry reference handouts (Periodic Table, Chemical Reference Sheet, etc) Notes Filler Paper for lecture notes Handouts or worksheets to supplement textbook Divided by chapter or unit – there are 7 separate sections for the first semester

21 E. Derived Units Combination of base units. Volume (m 3 or cm 3 ) length length length D = MVMV 1 cm 3 = 1 mL 1 dm 3 = 1 L Density (kg/m 3 or g/cm 3 ) mass per volume

22 F. Density Mass (g) Volume (cm 3 )

23 F. Density An object has a volume of 825 cm 3 and a density of 13.6 g/cm 3. Find its mass. GIVEN: V = 825 cm 3 D = 13.6 g/cm 3 M = ? WORK : M = DV M = (13.6 g/cm 3 )(825cm 3 ) M = 11,200 g

24 F. Density A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid? GIVEN: D = 0.87 g/mL V = ? M = 25 g WORK : V = M D V = 25 g 0.87 g/mL V = 29 mL

25 Homework Complete Worksheet Using Measurements – Chapter 2: due Monday (skip section on Dimensional Analysis – we will learn this next week ) Study for test tomorrow

26 I II III Dimensional Analysis Conversion Factors Problems

27 A. Problem-Solving Steps 1. Analyze 2. Plan 3. Compute 4. Evaluate

28 B. Dimensional Analysis Dimensional Analysis A tool often used in science for converting units within a measurement system Conversion Factor A numerical factor by which a quantity expressed in one system of units may be converted to another system

29 B. Dimensional Analysis The Factor-Label Method Units, or labels are canceled, or factored out

30 B. Dimensional Analysis Steps: 1. Identify starting & ending units. 2. Line up conversion factors so units cancel. 3. Multiply all top numbers & divide by each bottom number. 4. Check units & answer.

31 Fractions in which the numerator and denominator are EQUAL quantities expressed in different units Example: 1 in. = 2.54 cm Factors: 1 in. and 2.54 cm 2.54 cm 1 in. C. Conversion Factors

32 Conversion factor cancel By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers! How many minutes are in 2.5 hours ? 2.5 hr x xx x 60 min 1 hr = 150 min

33 Write conversion factors that relate each of the following pairs of units: 1. Liters and mL 2. Hours and minutes 3. Meters and kilometers C. Conversion Factors Learning Check: 1 L 1000 mL 1 hr 60 min 1000 m 1 km

34 You have $7.25 in your pocket in quarters. How many quarters do you have? You have $7.25 in your pocket in quarters. How many quarters do you have? 7.25 dollars 4 quarters 7.25 dollars 4 quarters 1 dollar 1 dollar X = 29 quarters D. Dimensional Analysis Practice

35 How many seconds are in 1.4 days? Plan: days hr min seconds 1.4 days x 24 hr x 60 min x 60 sec = 1 day1 hr 1 min D. Dimensional Analysis Practice sec sec

36 D. Dimensional Analysis Practice How many milliliters are in 1.00 quart of milk? 1.00 qt 1 L qt = 946 mL qtmL 1000 mL 1 L

37 You have 1.5 pounds of gold. Find its volume in cm 3 if the density of gold is 19.3 g/cm 3. lbcm lb 1 kg 2.2 lb = 35 cm g 1 kg 1 cm g D. Dimensional Analysis Practice

38 5) Your European hairdresser wants to cut your hair 8.0 cm shorter. How many inches will he be cutting off? 8.0 cm1 in 2.54 cm = 3.1 in cmin D. Dimensional Analysis Practice

39 6) Roswell football needs 550 cm for a 1st down. How many yards is this? 550 cm 1 in 2.54 cm = 6.0 yd cmyd 1 ft 12 in 1 yd 3 ft D. Dimensional Analysis Practice

40 7) A piece of wire is 1.3 m long. How many 1.5-cm pieces can be cut from this wire? 1.3 m 100 cm 1 m = 86 pieces mpieces 1 piece 1.5 cm D. Dimensional Analysis Practice

41 How many liters of water would fill a container that measures 75.0 in 3 ? 75.0 in 3 (2.54 cm) 3 (1 in) 3 = 1.23 L in 3 L 1 L 1000 cm 3 D. Dimensional Analysis Practice


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