CH 2: SCIENTIFIC MEASUREMENT. Chemistry is a lot of math!

Transcription

1 CH 2: SCIENTIFIC MEASUREMENT Chemistry is a lot of math!

2 WARM UP 1.Name 3 tools used for measurement. 2.What is a unit? 3.Give an example of a unit. 4.Why are units important.

3 CH 2 SCIENTIFIC MEASUREMENT Chemistry is a lot of math!

4 MAKING MEASUREMENTS Ch 2.2 Qualitative measurements: Give results in a descriptive and non-numerical form Example: Cookie Monster is Blue Quantitative measurements: Give results in a definite form usually as numbers and units Example: Cookie Monster ate 1 kg of cookies

5 QUALITATIVE OR QUANTITATIVE? The Big Mac is $2.29. The Pop Rocks are blue. The coffee is hot. The slurpee is 0 degrees Celsius.

6 Measurement a quantity that has both a number and a unit. For example I weigh 90! I make 1000 an hour! There are 72 in this class. Numbers with NO units mean NOTHING and will be marked WRONG on HW/Tests, etc. Measurements are fundamental to the experimental science.

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8 INTERNATIONAL SYSTEM OF UNITS

9 SI UNITS (SYSTEME INTERNATIONALE) Quantity Unit Symbol tool other Length Meter m Ruler, meter stick Mass Gram g Scale/ balance Not the same as weight Temperature Kelvin/ Celsius K / C Thermometer K=C+273 Time Seconds s Stopwatch Volume Liter or cm 3 L or cm 3 Graduated cylinder 1mL=1cm 3 Density Mass/Vol g/ml Scale & cylinder Derived unit Energy Joule J coulometer Can also use calorie Amount Mole Mol

10 SI UNITS (SYSTEME INTERNATIONALE) Meter (m) for length Use a meterstick to measure Kilogram (kg) for mass (1 kg = 2.2 lbs) Weight is NOT the same thing as mass! Use a scale to measure Kelvin (K) for temperature K = o C K = absolute zero Use a thermometer to measure o C is another option, but not Fahrenheit (in the metric Second (s) for time Use a stopwatch to measure Mole for the amount of substance We will talk about mole later Liter (L) or m 3 for volume Use a graduated cylinder to measure 1L = 1m 3 joule or calorie for energy We don t discuss this much in this class

11 MASS VS WEIGHT Mass: amount of matter Weight: measure of gravitational pull - Gravity does not affect mass

12 DERIVED UNITS: IT IS A COMBINATION OF UNITS Volume: ml or cm3 Density: D= m/v amount of space Ratio of mass to occupied by an volume object Speed: meters/ second

13 METRIC PREFIXES: The metric system utilizes prefixes based on powers of 10. Prefixes you need to memorize milli- (1/1000x), centi-(1/100x), kilo-(1000x)

14 Conversion factors: a ratio of equal proportions, expressed as a fraction Values can often be expressed in more than one form $1 = 4 quarters = 10 dimes = 20 nickels = 100 pennies 1 meter = 100cm = 1000mm = 0.001km equal values can be shown as a ratio equal to 1; such ratios are called conversion factors $1 60min 10dim es 1hr 1000m 1km 1km 1000m conversion factors are useful for solving problems in which given measurements must be expressed in some other unit.

15 METRIC PREFIXES Prefixes you need to memorize milli- (1/1000), centi-(1/100), kilo-(1000x) Adding prefixes, gives us a range of size measurements. Based on a system of 10 s (decimal system) NOTE that the bigger number goes with the smaller unit. 100 cm = 1 m

16 ALL METRIC UNITS INCREASE OR DECREASE BY A POWER OF 10.

17 Example 1: conversions a. convert 20 meters to millimeters 1. what are you cancelling and converting to? 2. how many of the smaller are in the larger? 1000mm = 1m 3. fill in a conversion factor 1000mm/1m 20,000mm

18 Example 2: conversions b. Convert 20 meters to kilometers 0.02 km

19 MORE EXAMPLES g = kg mm = m s = ms kg = mg cm 3 = m m 3 = mm 3 Answers 3) 0.6kg 4) 8.9m 5) 2300ms 6) 250,000mg 7) m 3 8)

20 CLASSWORK: Ch 2.2 Pg 42 #1-4

21 WHAT SI UNIT WOULD YOU USE TO MEASURE. 1. The length of a football 5. The distance from field? school to Sears? 2. The WIDTH of a strand of hair? 3. The mass of an elephant? 4. The mass of an ant? 6. The height of your desk? 7. The volume of water in a pool? 8. The volume of water in a spoon? 9. The temperature of this room?

22 Convert each of the following: kg = g cm = m ml = l mg = g cm = mm ml = l g = kg mm = m m = mm kg = mg Example: 3.68kg * 3.68kg * g 1 kg = 3680g Use table 2 on pg35! However you won t get the table for your quiz

23 kg = 3680 g cm = 5.68 m ml = 8.7 l mg = g cm = 1.01 mm ml = 0.25 l g = 0.6 kg mm = 8.9 m m = mm kg = mg

24 WHAT SI UNIT WOULD YOU USE TO MEASURE. 1. The length of a football 5. The distance from school field? Meters to union station? Kilometers 2. The WIDTH of a strand 6. The height of your desk? of hair? Mm, um cm 7. The volume of water in a pool? 3. The mass of an kl or km 3 elephant? km 8. The volume of water in a spoon? 4. The mass of an ant? ml or cm 3 9. The temperature of this Mg (grams) room? Kelvin (Celsius)

25 WARM UP Convert the following: g to cg 2. 69mm to cm km to cm

26 MORE EXAMPLES g = kg mm = m s = ms kg = mg cm 3 = m m 3 = mm 3 Answers 3) 0.6kg 4) 8.9m 5) 2300ms 6) 250,000mg 7) m 3 8) m

27 SCIENTIFIC NOTATION: move decimal point the number of times ex: 1*10 5 indicated by the power of means larger number - means smaller number Convert the following out of or into scientific notation 1) 6.5*10 4 = 2) 6.5*10-4 = ) = 3.5*10-4 4) = 3.5*10 4

28 DERIVED UNITS: IT IS A COMBINATION OF UNITS Volume: cm3 amount of space occupied by an object Density: D= m/v Ratio of mass to volume ml=cm3 Speed: meters/ second

29 DENSITY add the symbols <, >, or =to compare the blocks < < =

30 DENSITY: D= M/V Ex 1: A rock has a mass of 10 grams and a volume of 5 cm 3. Calculate its density. 10g / 5cm 3 = 2 g/cm 3 Units: Density = g 3 cm mass volume g or ml

31 D= m/v How can you find density from a graph? Density is the slope of the line of mass vs volume. D= m/v=slope = rise = run y 2- - y 1 g X 2 x 1 ml Ex: 11-3 g 11-3mL = 1 g/ml

32 1. What mineral is more dense? A, B, or C? - A: it has greatest slope 2. If you put equal volumes of A and B on a balance, which would have a larger mass? - A

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34 MORE DENSITY CALCULATIONS Water displacement is used to find the volume of unusual shape: volume = final initial water voluem 1. measure volume of water 50mL 2. Add an object and measure volume again 60ml 3. Subtract the volume of object+water from volume of just water 60-50=10mL Ex 2. The mass of 10 copper coins is 30 grams. The initial volume of water is 50mL and the volume with the coins if 55mL. Calculate the density of the copper coins.

35 Ex: 3. The density of silver is 10.0 g/cm 3. If you have a sample size of grams, what is the volume of the silver? HOW WOULD TEMP AFFECT DENSITY?? As temperature increases, what happens to density? If density deals with mass and volume Does temperature affect mass? Or volume?

36 1. The density of silver is 10.0 g/cm 3. If you have a sample size of grams, what is the volume of the silver? 2. If you have equal volumes of B(blue line) and C (red line). Which one has a larger mass?

37 WARM-UP A scientist wants to conduct an experiment measuring the effect of temperature on the density of nitrogen gas. 1. What units should be used for temperature and density? 2. What tools should be used to measure temperature and density? 3. What would be the independent and depend variables? 4. Control group and some constants?

38 CH 2.3 Accuracy: the closeness of measurements to the actual value Precision: The closeness of a set of measurements to each other 2 technicians measure the density of a new substance: A: 2.000, 1.999, and g/ml B: 2.5, 2.9, and 2.7 g/ml The correct value is g/ml Who is more accurate and who is more precise?

39 PERCENT ERROR: MEASURE OF HOW DIFFERENT YOUR VALUE IS FORM THE REAL VALUE Percent error = Value experimental Value accepted *100% Value accepted Example: The density of water at 4 o C is known to be 1.00 g/ml. Kayla experimentally found the density of water to be g/ml. What is her percent error?

40 SIGNIFICANT FIGURES (SIG. FIGS) IN MEASUREMENTS Significant Figures: all the digits in a measurement that are known with certainty plus one estimated digit

41 HOMEWORK HW: SI unit worksheet front side Quiz! Next class Use pg 42 #1,2 Part A and B of SI unit worksheet to study Table on pg 35

42 WARM-UP A scientist wants to conduct an experiment measuring the effect of temperature on the density of nitrogen gas. 1. What is the independent variable in this experiment? 2. The dependent variable? 3. What could be used as a control group? 4. What would be some constants? 5. What units should be used for temperature and density? 6. What tools should be used to measure temperature and density?

43 SCIENTIFIC NOTATION: move decimal point the number of times ex: 1*10 5 indicated by the power of means larger number - means smaller number Convert the following out of or into scientific notation 1) 6.5*10 4 = 2) 6.5*10-4 = ) = 3.5*10-4 4) = 3.5*10 4

44 SIGNIFICANT FIGURES (SIG. FIGS) IN MEASUREMENTS Significant Figures: all the digits in a measurement that are known with certainty plus one estimated digit

45 SIGNIFICANT FIGURES Ch 2.3 When we make quantitative measurements, we care about how good our data is. How we do this? Significant figures Slide 1 of 6

46 Rules for Significant Figures: 1. All nonzero numbers are significant page 47 and Zeros b/t nonzero digits are significant 3. Zeros appearing in front of all nonzero are not significant 4. Zeros at the end of a number and the right of a decimal point are significant 5. Zeros at the end of a number but to the left of a decimal point, if a decimal point is there, are significant. (NOT significant if no decimal) Examples: 245 G 3 sf 40.7 L km m 0.09 kg 85.00g m m

47 WHEN GIVEN A NUMBER, YOU MUST BE ABLE TO DETERMINE THE NUMBER OF SIG.FIGS. IN IT. a) 12,389 = All non-zero # s are significant b) = Zeros before a decimal are not imp unless it is part of a whole number c) = zeros in between # s are significant d) = Zeros after a decimal are significant IF THERE IS A WHOLE # e) x 10 7 = All numbers in the coefficient of a # in scientific notation are significant f) 24,000,000 = zeros w/out a decimal are NOT significant Perfect example of why sci.not. is so great gets rid of insig 0 s g) = zeros after a decimal but with no whole # are NEVER significant. Again, use sci.not.

48 Addition and Subtraction with Sig Figs: answer must have same # after the decimal as the number with the fewest digits to right of the decimal 25.1g g = 27.1g Multiplication and Division with Sig Figs: answer must use same # sig figs as the # with the fewest sig figs 3.05g / 8.47mL = 16mL = 20mL 0.360g 80.0g/ 5.0mL = 16mL 80.0g/ 5mL =

49 MATH WITH SIG FIGS (S.F) Conversions with s.f.: use same number of sig figs in the original measurement - the conversion factor is considered exact and does not count m * 100cm =460.8cm m Scientific Notation with Sig Figs: number is written to include only sig figs ex: 6.5* sig figs (65000) 2.04* sig figs ( )

50 SCIENTIFIC NOTATION: move decimal point the number of times ex: 1*10 5 indicated by the power of means move to the right - means move to the left 6.5*10 4 = *10-4 = = * = 3.5*10 4

51 Significant Figures A. State the number of significant digits in each measurement. 1) 2804 m 2) 2.84 km 3) m 4) m 5) 4.6 x 10 5 m 6) 4.06 x 10-5 m 7) 750 m 8) 75 m 9) 75,000 m 10) m 11) 75,000.0 m 12) 10 cm

52 Significant Figures Practice A. State the number of significant digits in each measurement. 1) 2804 m 4 2) 2.84 km 3 3) m 4 4) m 4 5) 4.6 x 10 5 m 2 6) 4.06 x 10-5 m 3 7) 750 m 2 or 3 8) 75 m 2 9) 75,000 m 2 10) m 4 11) 75,000.0 m 6 12) 10 cm 1 or 2

53 No warm up. Get a red pen (did you finish Sig Fig Practice part B? in classwork section of notebook) B. Solve the following problems and report answers with appropriate number of significant digits. 1) cm cm cm cm = 2) 1.62 m cm = 3) g g = 4) 1.31 cm x 2.3 cm = 5) m x m = 6) g / s = 7) m kg=

54 B practice 1) cm cm cm cm = 26.3 cm 2) 1.62 m cm = x 10 3 or 1362 cm 3) g g = 0.5 g 4) 1.31 cm x 2.3 cm = 3.0 cm 2 5) m x m = m 2 6) g / s = g/s 7) m kg= can t add m and kg

55 B. Solve the following problems and report answers with appropriate number of significant digits. 1) cm cm cm cm = 2) 1.6 km m cm = 3) g g = 4) m m = 5) m kg= 6) 1.31 cm x 2.3 cm = 7) m x m = 8) 20.2 cm / 7.41 s = 9) g / g =

56 1. What tool would you use to measure mass? 2. What unit would you use to measure mass? 3. What tool would you use to measure volume? 4. What unit(s) would you use to measure length?

57 NAME THE TOOL AND UNITS TO MEASURE EACH: 1. Length 2. Volume 3. Mass 4. Temperature 5. Density

58 1. LINEAR MEASUREMENTS The length, width, or height of something Tool? ruler, meter stick, etc. Units? Meter (m) Centimeters (cm) Millimeters (mm)

59 PRACTICE:

60 2. VOLUME The space matter takes up Tool? Graduated cylinder, beaker, etc. Units? Liter (L) Milliliters (ml) cm 3 MUST BE EYELEVEL TO MEASURE CORRECTLY!

61 PRACTICE:

62 3. MASS The quantity of matter Tool? balance, scale, etc. Units? Kilograms (kg) Grams (g) We use digital scales (usually) so just record what the scale says

63 MASS CONTINUED Scale must read zero before you place anything on it! If you want to measure the mass of something inside a container you must measure the empty container first. How much mass does the water have? g g

64 4. TEMPERATURE The amount of heat present Tool? thermometer Units? Degrees Celsius ( C)

65 5. DENSITY? The amount of matter in a space Units? g/cm 3 or g/ml Tool? scale and ruler or graduated cylinder