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I II III I. Units of Measurement (p. 33 - 39) CH. 2 - MEASUREMENT.

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Presentation on theme: "I II III I. Units of Measurement (p. 33 - 39) CH. 2 - MEASUREMENT."— Presentation transcript:

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

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

3 B. SI Units QuantityBase UnitAbbrev. Length Mass Time Temp meter kilogram second kelvin m kg s K Amountmolemol Symbol l m t T n

4 B. SI Units mega-M10 6 deci-d10 -1 centi-c10 -2 milli-m10 -3 PrefixSymbolFactor micro nano-n10 -9 pico-p kilo-k10 3 BASE UNIT

5 C. 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

6 D. Density Mass (g) Volume (cm 3 )

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

8 D. 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

9 D. 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

10 I II III II. Using Measurements (p ) CH. 2 - MEASUREMENT

11 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

12 B. Percent Error Indicates accuracy of a measurement your value accepted value

13 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 %

14 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 2.35 cm

15 C. Significant Figures Counting Sig Figs (Table 2-5, p.47) Count all numbers EXCEPT: Leading zeros Trailing zeros without a decimal point -- 2,500

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

17 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

18 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

19 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

20 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

21 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

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

23 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:

24 Chemistry Binder Organization

25 I II III III. Unit Conversions (p ) CH. 2 - MEASUREMENT

26 A. SI Prefix Conversions mega-M10 6 deci-d10 -1 centi-c10 -2 milli-m10 -3 PrefixSymbolFactor micro nano-n10 -9 pico-p kilo-k10 3 move left move right BASE UNIT

27 C. 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

28 D. Density Mass (g) Volume (cm 3 )

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

30 D. 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

31 D. 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

32 Homework P. 54 Practice problems 1 & 2

33 I II III Dimensional Analysis Conversion Factors Problems

34 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

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

36 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.

37 B. Dimensional Analysis Lining up conversion factors: 1 in = 2.54 cm 2.54 cm 1 in = 2.54 cm 1 in 1 in = 1 1 =

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

39 B. Dimensional Analysis 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

40 B. Dimensional Analysis 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

41 B. Dimensional Analysis 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 = 3.2 in cmin

42 B. Dimensional Analysis 6) Taft 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

43 B. Dimensional Analysis 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 cmpieces 1 piece 1.5 cm


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