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Ch. 5 Notes---Scientific Measurement Qualitative vs. Quantitative Qualitative measurements give results in a descriptive nonnumeric form. (The result of a measurement is an _____________ describing the object.) *Examples: ___________, ___________, long, __________... Quantitative measurements 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 _________ ___________. adjective shortheavycold number 600 lbs.5 ºC single valuetrue several othereach

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

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Significant Figures 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.) more marks reading in between the guess precise ALL second precision

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

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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

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The SI System (The Metric System) Here is a list of common units of measure used in science: Standard Metric Unit Quantity 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 _______ mass length volume time temperature 1 yard sugar cube’s 2.2 lbs. mass of a small paper clip dime

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The SI System (The Metric System)

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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 grams Liters meters mass cmdmm

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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 cm 3 1 L = 1 dm 3 For water only: 1 L = 1 dm 3 = 1 kg of water or 1 mL = 1 cm 3 = 1 g of water Practice Problems: (1) How many liters of water are there in 300 cm 3 ? ___________ (2) How many kg of water are there in 500 dL? _____________ 380,000 4.61 260 0.00145 0.0004 230 0.3 L 50 kg kilo- hecto- deka- deci- centi- milli-

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Metric Volume: Cubic Meter (m 3 ) 10 cm x 10 cm x 10 cm = Liter

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grams Liters meters Area and Volume Conversions If you see an exponent in the unit, that means when converting you will move the decimal point that many times more on the metric conversion scale. *Examples: cm 2 to m 2......move ___________ as many places m 3 to km 3......move _____ times as many places Practice Problems: 380 km 2 = _________________m 2 4.61 mm 3 = _______________cm 3 k h da g, L, m d c m twice 3 380,000,000 0.00461

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Scientific Notation Scientific notation is a way of representing really large or small numbers using powers of 10. *Examples: 5,203,000,000,000 miles = 5.203 x 10 12 miles 0.000 000 042 mm = 4.2 x 10 −8 mm Steps for Writing Numbers in Scientific Notation (1) Write down all the sig. figs. (2) Put the decimal point between the first and second digit. (3) Write “x 10” (4) Count how many places the decimal point has moved from its original location. This will be the exponent...either + or −. (5) If the original # was greater than 1, the exponent is (__), and if the original # was less than 1, the exponent is (__)....(In other words, large numbers have (__) exponents, and small numbers have (_) exponents. + + − −

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477,000,000 miles = _______________miles 0.000 910 m = _________________ m 6.30 x 10 9 miles = ___________________ miles 3.88 x 10 −6 kg = __________________ kg Scientific Notation Practice Problems: Write the following measurements in scientific notation or back to their expanded form. 4.77 x 10 8 9.10 x 10 −4 6,300,000,000 0.00000388 −

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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 ratioequivalent 60 77 11 top bottom

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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. If your units did not ________ ______ correctly, you’ve messed up! Given Unknown conversion factors multiply divide cancel out

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Practice Problems: (1)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 1 day 3.25 days x = 78 hrs 1 ft 12 in. 1 yard 504 in. x x= 14 yards 60 sec 1 hr1 min 26,748 sec x x = 0.30958 days 3 ft 60 min x 24 hrs 1 day

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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) (3) Convert 33,500 in 2 to m 2 (5280 ft = 1609 m) (12 inches = 1 foot) 1 ft 12 in. 1609 m 33,500 in 2 x x = 21.6 m 2 5280 ft 1 mile 1609 m 3600 sec330m x x= 738 miles/hr 1 hrsec 1 kg 1000 g 2.2 lbs1.0 g x x 8.3 lbs/gal 1 kgmL 1000 mL x = 1 L 3.78 L x 1 gal 22 numerator denominator top bottom

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