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Ch. 5 Notes---Scientific Measurement

Ch. 5 Notes---Scientific Measurement. adjective. Qualitative vs. Quantitative Qualitative measurements give results in a descriptive nonnumeric form. (The result of a measurement is an _____________ describing the object.) ‏ *Examples: ___________, ___________, long, __________...

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Ch. 5 Notes---Scientific Measurement

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  1. Ch. 5 Notes---Scientific Measurement adjective Qualitative vs. Quantitative • Qualitativemeasurements give results in a descriptive nonnumeric form. (The result of a measurement is an _____________ describing the object.)‏ *Examples: ___________, ___________, long, __________... • Quantitativemeasurements give results in numeric form. (The results of a measurement contain a _____________.)‏ *Examples: 4’6”, __________, 22 meters, __________... Accuracy vs. Precision • Accuracy is how close a ___________ measurement is to the ________ __________ of whatever is being measured. • Precision is how close ___________ measurements are to _________ ___________. short heavy cold number 600 lbs. 5 ºC single true value several each other

  2. Practice Problem:Describe the shots for the targets. Bad Accuracy & Bad Precision Good Accuracy & Bad Precision Bad Accuracy & Good Precision Good Accuracy & Good Precision

  3. Significant Figures precision precise • Significant figures are used to determine the ______________ of a measurement. (It is a way of indicating how __________ a measurement is.)‏ *Example: A scale may read a person’s weight as 135 lbs. Another scale may read the person’s weight as 135.13 lbs. The ___________ scale is more precise. It also has ______ significant figures in the measurement. • Whenever you are measuring a value, (such as the length of an object with a ruler), it must be recorded with the correct number of sig. figs. • Record ______ the numbers of the measurement known for sure. • Record one last digit for the measurement that is estimated. (This means that you will be ________________________________ __________ of the device and taking a __________ at what the next number is.)‏ second more ALL reading in between the marks guess

  4. Significant Figures • Practice Problems:What is the length recorded to the correct number of significant figures? length = ________cm 11.65 (cm) 10 20 30 40 50 60 70 80 90 100 length = ________cm 58

  5. For Example • Lets say you are finding the average mass of beans. You would count how many beans you had and then find the mass of the beans. • 26 beans have a mass of 44.56 grams. • 44.56 grams ÷26 =1.713846154 grams So then what should your written answer be? How many decimal points did you have in your measurement? Rounded answer = 2 1.71 grams

  6. Rules for Counting Significant Figures in a Measurement • When you are given a measurement, you will need to be aware of how many sig. figs. the value contains. (You’ll see why later on in this chapter.)‏ • Here is how you count the number of sig. figs. in a given measurement: • #1 (Non-Zero Rule): All digits 1-9 are significant. • *Examples: 2.35 g =_____S.F. 2200 g = _____ S.F. • #2 (Straddle Rule): Zeros between two sig. figs. are significant. • *Examples: 205 m =_____S.F. 80.04 m =_____S.F. • 7070700 cm =_____S.F. • #3 (Righty-Righty Rule): Zeros to the right of a decimal point AND anywhere to the right of a sig. fig. are significant. • *Examples: 2.30 sec. =_____S.F. 20.0 sec. =_____S.F. • 0.003060 km =_____S.F. 3 2 3 4 5 3 3 4

  7. Rules for Counting Significant Figures in a Measurement • #4 (Bar Rule): Any zeros that have a bar placed over them are sig. (This will only be used for zeros that are not already significant because of Rules 2 & 3.)‏ • *Examples:3,000,000 m/s =_____S.F. 20 lbs =____S.F. • #5 (Counting Rule): Any time the measurement is determined by simply counting the number of objects, the value has an infinite number of sig. figs. (This also includes any conversion factor involving counting.) • *Examples:15 students =_____S.F. 29 pencils = ____S.F. • 7 days/week =____S.F. 60 sec/min =____S.F. 4 2 ∞ ∞ ∞ ∞

  8. decimal places Calculations Using Sig. Figs. • When adding or subtracting measurements, all answers are to be rounded off to the least # of ___________ __________ found in the original measurements. • When multiplying or dividing measurements, all answers are to be rounded off to the least # of _________ _________ found in the original measurements. Practice Problems: 2.83 cm + 4.009 cm − 2.1 cm = 4.739 cm ≈_____ cm 36.4 m x 2.7 m = 98.28 m2 ≈ _____ m2 0.52 g ÷ 0.00888 mL = 5.855855 g/mL ≈ ____ g/mL Example: + ≈ 157.17 (only keep 2 decimal places)‏ significant figures (only keep 1 decimal place)‏ 4.7 98 (only keep 2 sig. figs)‏ 5.9 (only keep 2 sig. figs)‏

  9. Mass vs. Weight matter • Mass depends on the amount of ___________ in the object. • Weight depends on the force of ____________ acting on the object. • ______________ may change as you move from one location to another; ____________ will not. • You have the same ____________ on the moon as on the earth, but you ___________ less since there is less _________ on the moon. gravity Weight mass Mass = 80 kg Weight = 176 lbs. mass weigh gravity Mass = 80 kg Weight = 29 lbs.

  10. mass • The SI System (The Metric System)‏ • Here is a list of common units of measure used in science: • Standard Metric UnitQuantity Measured • kilogram, (gram) ______________ • meter ______________ • cubic meter, (liter) ______________ • seconds ______________ • Kelvin, (˚Celsius) _____________ • The following are common approximations used to convert from our English system of units to the metric system: • 1 m ≈ _________ 1 kg ≈ _______ 1 L ≈ 1.06 quarts • 1.609 km ≈ 1 mile 1 gram ≈ ______________________ • 1mL ≈ _____________ volume 1mm ≈ thickness of a _______ length volume time temperature 1 yard 2.2 lbs. mass of a small paper clip sugar cube’s dime

  11. The SI System (The Metric System)‏

  12. mass Metric Conversions • The metric system prefixes are based on factors of _______. Here is a list of the common prefixes used in chemistry: kilo- hecto- deka- deci- centi- milli- • The box in the middle represents the standard unit of measure such as grams, liters, or meters. • Moving from one prefix to another involves a factor of 10. *Example: 1000 millimeters = 100 ____ = 10 _____ = 1 _____ • The prefixes are abbreviated as follows: k h da g, L, m d c m *Examples of measurements: 5 km 2 dL 27 dag 3 m 45 mm cm dm m grams Liters meters

  13. Metric Conversions • To convert from one prefix to another, simply count how many places you move on the scale above, and that is the same # of places the decimal point will move in the same direction. Practice Problems: 380 km = ______________m 1.45 mm = _________m 461 mL = ____________dL 0.4 cg = ____________ dag 0.26 g =_____________ mg 230,000 m = _______km Other Metric Equivalents 1 mL = 1 cm3 1 L = 1 dm3 For water only: 1 L = 1 dm3 = 1 kg of water or 1 mL = 1 cm3 = 1 g of water Practice Problems: (1) How many liters of water are there in 300 cm3 ? ___________ (2) How many kg of water are there in 500 dL? _____________ kilo- hecto- deka- deci- centi- milli- 380,000 0.00145 4.61 0.0004 260 230 0.3 L 50 kg

  14. Metric Volume: Cubic Meter (m3) 10 cm x 10 cm x 10 cm = Liter

  15. Ch. 4 Problem Solving in Chemistry • Dimensional Analysis • Used in _______________ problems. • *Example: How many seconds are there in 3 weeks? • A method of keeping track of the_____________. • Conversion Factor • A ________ of units that are _________________ to one another. • *Examples: 1 min/ ___ sec (or ___ sec/ 1 min) • ___ days/ 1 week (or 1 week/ ___ days) • 1000 m/ ___ km (or ___ km/ 1000 m) • Conversion factors need to be set up so that when multiplied, the unit of the “Given” cancel out and you are left with the “Unknown” unit. • In other words, the “Unknown” unit will go on _____ and the “Given” unit will go on the ___________ of the ratio. conversion units ratio equivalent 60 60 7 7 1 1 top bottom

  16. How to Use Dimensional Analysis to Solve Conversion Problems • Step 1: Identify the “________”. This is typically the only number given in the problem. This is your starting point. Write it down! Then write “x _________”. This will be the first conversion factor ratio. • Step 2: Identify the “____________”. This is what are you trying to figure out. • Step 3: Identify the ____________ _________. Sometimes you will simply be given them in the problem ahead of time. • Step 4: By using these conversion factors, begin planning a solution to convert from the given to the unknown. • Step 5: When your conversion factors are set up, __________ all the numbers on top of your ratios, and ____________ by all the numbers on bottom. Given Unknown conversion factors multiply divide If your units did not ________ ______ correctly, you’ve messed up! cancel out

  17. Practice Problems: • How many hours are there in 3.25 days? • (2) How many yards are there in 504 inches? • (3) How many days are there in 26,748 seconds? 24 hrs 3.25 days 78 hrs = x 1 day 1 ft 1 yard 504 in. 14 yards x = x 12 in. 3 ft 1 min 1 hr 1 day 26,748 sec 0.30958 days x x x = 60 sec 60 min 24 hrs

  18. Converting Complex Units • A complex unit is a measurement with a unit in the _____________ and ______________. • *Example: 55 miles/hour 17 meters/sec 18 g/mL • To convert complex units, simply follow the same procedure as before by converting the units on ______ first. Then convert the units on __________ next. • Practice Problems: (1) The speed of sound is about 330 meters/sec. What is the speed of sound in units of miles/hour? (1609 m = 1 mile) • (2) The density of water is 1.0 g/mL. What is the density of water in units of lbs/gallon? (2.2 lbs = 1 kg) (3.78 L = 1 gal) numerator denominator top bottom 330m 1 mile 3600 sec 738 miles/hr x = x sec 1609 m 1 hr 1.0 g 1 kg 2.2 lbs 1000 mL 3.78 L 8.3 lbs/gal x x x x = mL 1000 g 1 kg 1 L 1 gal

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