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Chemistry The Importance in Measurement

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What type of Measurement are made in Chemistry? 1.Qualitative Measurements Descriptive, non-numerical formDescriptive, non-numerical form Color, shape, size, feelings, textureColor, shape, size, feelings, textureExample: The basketball is round and brown. 2.Quantitative Measurements Definite form with numbers AND unitsDefinite form with numbers AND units Mass, volume, temperature, etc.Mass, volume, temperature, etc.Example: The basketball has a diameter of 31 cm and a pressure of 12 lbs/in 2.

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In science, we deal with some very LARGE numbers: 1 mole = 602000000000000000000000 In science, we deal with some very SMALL numbers: Mass of an electron = 0.000000000000000000000000000000091 kg Scientific Notation

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Imagine the difficulty of calculating the mass of 1 mole of electrons! 0.000000000000000000000000000000091 kg x 602000000000000000000000 x 602000000000000000000000 ???????????????????????????????????

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Scientific Notation: A method of representing very large or very small numbers in the form: M x 10 n M x 10 n M is a number between 1 and 10 n is an integer # of times to move the decimal If n is negative, the number is really small If n is positive, the number is really large.

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2 500 000 000 Step #1: Insert an understood decimal point. Step #2: Decide where the decimal must end up so that one number is to its left up so that one number is to its left Step #3: Count how many places you bounce the decimal point the decimal point 1234567 8 9 Step #4: Re-write in the form M x 10 n

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2.5 x 10 9 The exponent is the number of places we moved the decimal. Since it was a large number, the exponent is positive.

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0.0000579 Step #2: Decide where the decimal must end up so that one number is to its left up so that one number is to its left Step #3: Count how many places you bounce the decimal point the decimal point Step #4: Re-write in the form M x 10 n 12345

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5.79 x 10 -5 The exponent is negative because the number we started with was less than 1.

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PERFORMING CALCULATIONS IN SCIENTIFIC NOTATION ADDITION AND SUBTRACTION

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4 x 10 6 + 3 x 10 6 IF the exponents are the same: 1. add or subtract the numbers in front 2. bring the exponent down unchanged. 7 x 10 6

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4 x 10 6 - 3 x 10 6 The same holds true for subtraction in scientific notation. 1 x 10 6

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4 x 10 6 + 3 x 10 5 If the exponents are NOT the same, we must move a decimal to make them the same.

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4.00 x 10 6 + 3.00 x 10 5 Student A 40.0 x 10 5 43.00 x 10 5 Is this good scientific notation? NO! = 4.300 x 10 6 To avoid this problem, move the decimal on the smaller number!

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4.00 x 10 6 + 3.00 x 10 5 Student B.30 x 10 6 4.30 x 10 6 Is this good scientific notation? YES!

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A Problem for you 2.37 x 10 -6 + 3.48 x 10 -4

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2.37 x 10 -6 + 3.48 x 10 -4 Solution 002.37 x 10 -6 0.0237 x 10 -4 3.5037 x 10 -4

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PERFORMING CALCULATIONS IN SCIENTIFIC NOTATION MULTIPLICATION AND DIVISION

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4 x 10 6 x 3 x 10 6 IF the problem is multiplication: 1. Multiply the numbers as usual 2. add the exponent. 12 x 10 12

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24 x 10 9 3 x 10 6 IF the problem is division: 1. Divide the numbers as usual 2. subtract the exponents: numerator - denominator 8 x 10 3

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Calculate the following answer: 0.000 000 000 000 000 000 000 000 000 000 91 kg 0.000 000 000 000 000 000 000 000 000 000 91 kg ______ x 602 000 000 000 000 000 000 000 ??????????????????????????????????? 9.1 x 10 -31 x 6.02 x 10 23 54.782 x 10 -8 5.4782 x 10 -7 kg

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Practice Problems #1 1. 5.7 x 10 6 + 3 x 10 5 2. 3.8 x 10 5 - 2.1 x 10 6 3. 1.35 x 10 7 + 8 x 10 5 4. 8.52 x 10 -9 + 2.16 x 10 -9

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Practice Problems #2 5. 7 x 10 6 / 2 x 10 4 6. 5 x 10 8 x 5 x 10 3 7. 5 x 10 3 / 2 x 10 3 8. 2 x 10 7 x 4 x 10 -9

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Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value. Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor precise Precise but not accurate Precise AND accurate

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Percent Error Accepted Value Correct value based on reliable references. Example: Boiling Point of water is 100C Experimental Value Value measure in lab. Example: Boiling Point measured in lab reads 99.1C Percent Error = x 100 | experimental value accepted value | accepted value |99.1 100| 100 100 x 100 0.9 0.9 100 100 x 100 = 0.9% error Errors less than 5-10% is acceptable!

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International System of Units (SI)

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The Fundamental SI Units (le Systme International, SI) QuantitySI Base UnitSymbolOther Symbols Lengthmeterm Volumecubic meterm3m3 liter (L) Masskilogramkm Density grams / cubic centimeter g/cm 3 grams / milliliter (g/mL) TemperaturekelvinKdegree Celcius (C) Timeseconds PressurepascalPaatmosphere (atm) EnergyjouleJcalorie (cal) Amt of Subs.molemol

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Prefixes in Measurements PrefixSymbolFactor Scientific Notation mega-M1 000 00010 6 kilo-k1 00010 3 deci-d1 / 1010 -1 centi-c1 / 10010 -2 milli-m1 / 100010 -3 micro-1 / 1 000 00010 -6 nano-n1 / 1 000 000 00010 -9 pico-p1 / 1 000 000 000 00010 -12

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Units of Length UnitSymbolRelationshipExample Kilometerkm1 km = 10 3 mLength of 5 city blocks Metermbase unitHeight of door knob Decimeterdm10 1 dm = 1 mDiameter of orange Centimetercm10 2 cm = 1 mWidth of button Millimetermm10 3 mm = 1 mThickness of dime Micrometermm10 6 m = 1 mDiameter of a bacteria Nanometernm10 9 nm = 1 mThickness of an RNA

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Units of Volume UnitSymbolRelationshipExample LiterLbase unitQuart of Milk MillitermL10 3 mL = 1 L20 drops of water Cubic Centimeter cm 3 1 cm 3 = 1 mLcube of sugar MicroliterLL10 6 L = 1 Lcrystal of table salt

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Units of Mass UnitSymbolRelationshipExample Kilogramkg base unit 1 kg = 10 3 g small textbook Gramg1 g = 10 -3 kgdollar bill Milligrammg10 3 mg = 1 gten grains of salt Microgramgg10 6 g = 1 g particle of baking powder