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WHAT IS CHEMISTRY? Demo: Let’s make slime! Chemistry – the study of matter and its reactions Matter - anything that has mass and volume - Includes living and non-living things AREAS OF STUDY Organic Chemistry – C compounds Inorganic Chemistry – non-C compounds Biochemistry – study of living matter Analytical Chem. – composition of matter Physical Chem. – mechanisms, rate and energy transfer THINKING LIKE A SCIENTIST 1. 2. 3. The Scientific Method Analyze - identify the known - find the unknown Calculate - make conversions - solve for the unknown Evaluate - does the answer make sense Theory – a well tested explanation for a set of observations Law – concise statement that summarizes a set of results MATHEMATICAL CALCULATIONS I Scientific Notation (Exponential form) – used to express very large and very small numbers coefficient X 10 to a power ↓ ↓ > 1 < 10 the # of times the coefficient is multiplied by 10 to equal the standard number Standard Form Exponential Form 25,000 = 2.5 x 104 DETERMINING EXPONENTIAL FORM For Numbers > 10 Exponent = the number of times the decimal point is moved to the left to produce a coefficient between 1 and 10 Ex. 8,200,000 6 places = 8.2 x 106 , or, 8.2 is multiplied by 10 - 6 times to equal 8,200,000 2,250 = For numbers < 1 The exponent is negative * Indicates the number of times the coefficient is divided by 10 to get to the standard To convert from the standard – count the number of times the decimal must be moved to get to the coefficient Ex. 0.00075 = 4 places = 7.5 x 10-4 or, 7.5 divided by 10, 4 times CONVERTING FROM SCIENTIFIC NOTATION TO STANDARD FORM 1. 2. For + exponents → move the decimal to the right For (–) exponents → move the decimal point to the left Ex. 3.3 x 10-6 = ______________ 1.5 x 103 = ______________ MULTIPLYING AND DIVIDING Multiplying 1. Multiply the coefficients 2. ADD the exponents 3. Re-configure if necessary Ex. (2 x 102) x (4 x 106) = ___________ (3.1 x 104) x (5 x 10-7) = ___________ Dividing 1. 2. 3. DIVIDE the coefficients SUBTRACT the exponents Re-configure if necessary Ex. 3.0 x 105 = ______________ 6.0 x 102 3.0 x 105 6.0 x 10-3 = ______________ ADDING AND SUBTRACTING 1. 2. 3. 4. Both exponents MUST be the same Convert one number if necessary Add (or subtract) the coefficients Re-configure if necessary Ex. 8.0 x 102 + 5.4 x 103 = 8.0 x 102 + 54 x 102 = _____________ II SIGNIFICANT FIGURES Those digits (of a measurement) known with certainty plus the right most digit that is estimated. Ex. Counting Sig Figs 1. Every non-zero digit is significant 2. Zeros in the middle of a # are significant ex. 605 = 3 sig figs 3. Zeros at the beginning of a number are NOT significant = placeholders ex. .0025 = 2 sig figs 4. Zeros at the end of a number are only significant if they follow a decimal ex. 7500 = 2 sig figs ex. 75.00 = 4 sig figs 5. Counted numbers = unlimited sig figs The Atlantic and Pacific Rule (Easy way to count sig figs) Does the number have a decimal point? Decimal point Absent - Atlantic Ocean Decimal point Present - Pacific Ocean source Decimal point present: •Start on Pacific (left) side of number • Start counting with first non-zero digit and count until the end of the number 2545.300 g has 7 sig figs 0.004530 km has 4 sig figs Decimal point absent: • Start on Atlantic (right) side of number •Start counting with first non-zero digit and count until the end of the number 5400 m 5431 m has 2 sig figs has 4 sig figs Calculations with sig figs Multiplication and Division The answer can have only as many significant figures as the number with the least number of sig figs Calculations are Rounded Off 24.56 cm X 14 cm = a) 343.84 cm2 b) 343.8 cm2 c) 343 cm2 d) 340 cm2 EXAMPLE 2.2 X 104 X 3.12 X 106 Answer = 6.9 x 1010 Addition and Subtraction The answer can have only as many decimal places as the number with the least number of decimal places Calculations are Rounded Off 422.63 cm 29.472 cm +________________ 115.9 cm a) 568.002 cm b) 568.00 cm c) 568.0 cm d) 568 cm MEASUREMENTS Accuracy – a measure of how close a measurement comes to the true value of whatever is being measured To evaluate – compare the measured value to the true value Precision – a measure of how close a series of measurements are to one another To evaluate – compare the values of 2 or more repeated measurements ACCURACY AND PRECISION III CALCULATING ERROR Error – difference between the accepted value and the experimental value may be + (greater) or – (less) Calculated by % = Percent Error % Error = Exp Value – Accepted Value x 100 Accepted Value EXAMPLE A student measured a sample of NaCl to be 22.75 grams. The true value of the sample was 22.50 grams. Calculate the % error Known: Measured sample = 22.75 g True mass = 22.50 g Unknown: % error Solve: 22.75 g – 22.50 g x 100 = 22.50 g 0.25 x 100 = 1.1 % 22.50 HW – PG 72 #’s 13-15 Measured value = 124.1o C Actual value = 125.7o C Unknown = % Error Solve 124.1o C – 125.7o C x 100 = - 1.6o C = 125.7o C 125.7o C 0.0127287 x 100 = 1.272 % 13. 14. 11 soccer players 10, 800 m 0.070020 m 5.00 m3 note: counted items have unlimited sig figs 15. a) b) (5.3 x 104) + (1.3 x 104) = 6.6 x 104 (7.2 x 10-4) / (1.8 x 103) = 4.0 x 10-7 c. 104 x 10-3 x 106 = 107 d. (9.12 x 10-1) – (4.7 x 10-2) = (9.12 x 10-1) – (.47 x 10-1) = 8.7 x 10-1 e. (5.4 x 104) x (3.5 x 109) = 18.9 x 1013 = 1.89 x 1014 = 1.9 x 1014 International System of Units 1790 – French Academy of Sciences created the metric system Based on 3 Requirements Basic Standard = Earth 1. The unit of length was to be a portion of the Earth's circumference Internal Consistency 2. Units for capacity (volume or space) and mass related to the unit of length Ease of Use - Calculations 3. Larger and smaller units are created by multiplying or dividing the basic units by factors of 10 Smaller & Larger Units ►1/10 of a meter = decimeter ►1/100 of a meter = centimeter ►1/1000 of a meter = millimeter ►10 meters = dekameter ►100 meters = hectometer ►1000 meters = kilometer Prototype kilogram in France Systeme International (SI) ►Based on the metric system, invented in 1790* Originally, earth-based standards Volume & mass linked to length Larger & smaller multiples of each unit related by powers of 10 *updated in 1960 What is a meter? 1790: 1/10,000,000 th of the distance from the North pole to the equator 1983: the distance light travels in a vacuum in 1/299,792,458 th of a second What is a Liter? • defined as a cube measuring 10 centimeters on each side, or 1000 cm3 10 cm • based on the meter, which is based on the Earth 10 cm What is a kilogram? mass of 1 Liter of water at 4°C 10 cm Why water? 10 cm So… the kilogram is based on the liter, which is really based on the meter, which is really based on the Earth What is a second? The second was originally defined as 1/86,400th of the average solar day Now: defined in terms of electron transitions in Cs-133 7 Fundamental Quantities of SI Quantity Length Mass Name Abbreviation meter kilogram m kg Time second s Temperature kelvin K Amount of Substance Mole mol Luminous Intensity candela cd Electric Current ampere A Derived Units ► Combinations of fundamental units ► Many, many derived units ► Examples: Speed or distance/time = m/sec Area or Length X Width = cm2 Volume or Length X Width X Height = cm3 Density or Mass / Volume = g/ml What is a kelvin? The kelvin is defined in terms of water & absolute zero 0 K = Absolute zero bp of H2O = 100C = 373 K mp of H2O = 0C = 273 K What is a mole? ►The amount of substance which has as many elementary particles as there are atoms in 0.012 kilogram (12 grams) of carbon-12 METRIC MEASUREMENTS MEASUREMENT 1. 2. 3. 4. 5. Length Mass Volume Temperature Time DEFINITION STANDARD UNIT Prefixes in the SI System Prefix Symbol Value Power Use Giga G 1,000,000,000 109 Gigabyte Mega M 1,000,000 106 Megamillion Kilo k 1,000 103 kilometer deci d 0.1 10-1 decimeter centi c 0.01 10-2 centimeter milli m 0.001 10-3 millimeter micro 0.000001 10-6 micrometer nano n 0.000000001 10-9 nanometer Prefixes ►The prefixes can be used with all 7 fundamental units! Kilometer Milliliter Centigram Microsecond Nanokelvin IV METRIC CONVERSIONS 1. Temperature Conversions K = oC + 273 oC = K – 273 ex. BP of H2O is 100o C BP of H2O in K = ex. FP of H2O = - 273o K FP of H2O in o C = CONVERSIONS 2. Metric Conversions – used to measure quantities in different ways Ex. 1 meter = 10 decimeters = 100 cm = 1000 mm Conversion Factor – a ratio of equivalent measurements - used to change one unit to another unit - the value of the numeral will change (in multiples of 10) - actual size and quantity stays the same ex. 1 m = conversion factor 100 cm = 100 cm 1m Conversion Factors Write the conversion factors for the following: l to ml = Kg to g = cm to mm = l to μl = Conversion Problems ► Convert 3.5 kg to g ► Known: 1000 g = 1 kg ► Unknown: # g ► Calculate ► 3.5 kg x 1000 g = 3,500 g ► 1 kg ► Note: conversion factor must be written to cancel all units except the unknown unit. V EQUATIONS Density = Mass / Volume How would you find mass if you are given the density and the volume? Solve for M M=DxV Solve for V V = M/D TO MODIFY AN EQUATION Change Sides……..Change Signs D = M V V=M D M = VD EXAMPLE P1 x V1 = P2 x V2 SOLVE FOR P2 P2 = P1 x V1 V2 CALCULATIONS WITH UNITS Density = g/cm3 Mass = g Volume = cm3 Mass = Density x volume g = g cm3 x cm3 CALCULATIONS WITH UNITS P2 = P1 x V1 V2 atm = atm x ml ml P in atm V in ml