CHEM 1101, week 2
CHEM 1101, week 2 CHE 1101
Popular in Introduction Chemistry I
Popular in Chemistry
This 8 page Class Notes was uploaded by Ashton Cress on Tuesday September 6, 2016. The Class Notes belongs to CHE 1101 at Appalachian State University taught by Dr. Brittany Lauren Woods in Fall 2016. Since its upload, it has received 62 views. For similar materials see Introduction Chemistry I in Chemistry at Appalachian State University.
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Date Created: 09/06/16
Name examples of elements What is a chemical symbol? Abbreviation of the elements name -Tungsten = W (wolfram) -Sodium = Na = Natrium usually derived from Italian, Greek, or European names First letter is always capitalized, second letter is not Compounds= Pure Substance found from two or more different elements, combined in the same proportions by mass Water will always be H O2 Mixtures= Impure Variable compositions -sugar water -oil and water -Heterogeneous/Homogeneous Physical and Chemical Properties Molecules- can only have one type of atom Pure substances and mixtures Mixtures are not just liquids— they can be solids, liquids, or gas Mixtures A mixture can be defined by either being a Heterogeneous mixture or a Homogeneous mixture Heterogeneous Consists of two or more regions/phases -solid/liquid/gas Distinctly different properties Homogeneous Same properties throughout Solution If a homogeneous matter can be separated physically, it’s a mixture Homogeneous matter If a homogeneous matter cannot be separated physically, it is a pure substance Physical vs Chemical Change Physical: No new substances form -substance may change state or the proportions melting candle -may look different but is the same chemical compound -properties do not change melting/freezing/boiling point Chemical: Molecules change, undergoes chemical reaction e.x burning candle -formation of a new substance or compound -involves changing chemical makeup of substances -new substances has different physical properties Chemical: -can’t be separated by physical means -composition changes through chemical reaction Physical vs Chemical Properties Physical: size difference Shape difference Chemical: color change Intensive vs extensive physical properties Intensive: INDEPENDENT -properties independent of size samples - color, boiling/freezing/melting point, density - can be used to identify substances Extensive: DEPENDENT -Properties that are dependent on sample size -mass/volume Measurements of Chemical and Physical properties RECALL: SCIENTIFIC METHOD Quantitative: Observations Numerical Data Measured with instruments i.e Melting/boiling/freezing points, volume, mass qualitative: senses colors taste Measurements 1. Measurements involve comparison a. Always measure relative to reference b. Measurements= number+unit c. Meaningless without units 2. Measurements are not exact Units Two Types: 1. Fundamental (or based) Units 2. Derived Units Measurements Unit Abbreviation Length Meter M mass Kilogram Kg time Second S Electric current Ampere A Temperature Kelvin K Amount of substance Mole mol Derived Units All physical quantities will have units that are combinations of the 7 base units Units undergo the same kinds of mathematical operations that numbers do i.e velocity= distance / time V= meters / seconds= m/s Metric system Prefix Abbreviations Meaning Giga G 10^9 Mega M 10^6 Kilo K 10^3 Deci d 10^-1 Centi c 10^-2 Milli M 10^-3 Micro μa 10^-6 Nano n 10^-9 Pico p 10^-12 Femto f 10^-15 easy conversions is to move the decimal points! Lab measurements Volume: SI unit- m Liters mL measured using graduate glassware 1L=1dm EXACTLY 1L=1000 mL 1mL= 1cm 3 Mass: SI unit- Kg g (grams) measured by using a balance or scale 1Kg= 1000g Length: SI unit- m mm (millimeters) cm (centimeters) measured by using a ruler 1m=100cm=1000mm 10cm=100mm Temperature: SI unit- Kelvin (K) Celcius (C ) o Fahrenheit (F ) measured by thermometer Temperature: K= C+273.15 oC= 5/9( F-32) oF= 9/5( C)+32 No degree symbol for K Density Used to characterize substances Defined as 3ass/Volume or M/V Units: g/cm = g/mL Originally based on mass (density was defined as the mass of 1.00 gram of pure water ratio of an objects mass to its volume) Intensive property (size dependent) -determined by taking ratio of two extensive properties (size dependent) -frequently ratio size of 2 dependent properties leads to size independent property -sample size cancels Most substances expand slightly when heated -same mass -larger volume -less dense Density decreased slightly as temperature increases Liquids and solids -change is very small -can ignore except in very precise calculations Density is useful to transfer between mass and volume of a substance Density as a conversion tool Rearrange to get information needed d= g/cm = g/mL If you know the weight and volume, you can calculate density If you know the density and weight, you can calculate volume V= m/d If you know the density and volume, you can find the weight M= d(v) measured using instruments (balance,scale,graduated cylinder,beaker,etc.) RECALL: measurements have uncertainties Uncertainty All scientific measurements are subject to error Errors are reflected in the number of figures reported for that measurement Errors are also reflected in the observation that two successive measurements of the same quantity are different Uncertainty in measurements Measurements all inexact -contain uncertainties or errors sources of errors -limitations of reading instruments ways to minimize errors -take a series of measurements -data clusters around a central value -calculate average or mean values -reporting all values Least certain measurement used in a calculation limits the certainty of the quantity Final estimate should be reported with only one uncertain digit Accuracy and precision Accuracy -How close measurement is to true or accepted true value -Measuring device must be calibrated with standard preference to give correct value Precision -how well set of repeated measurements of same quantity agree with each other -More significant figures equals more precise measurements importance of reliable measurements To trust conclusions drawn from measurements -must know how they are reliable -must be sure they are accurate -measured values must be close to true values -otherwise, can’t trust results -can’t make conclusions based on those results -must have sufficient precision to be meaningful Significant Figures Scientific Convention -all digits in measurement up to and including first estimated digits are significant Number of certain digits and first certain digit Digits in Measurement from first non-zero number to the left to first estimated digit on right 1. All Non-Zero numbers are significant 2. Zeros between non-zero digits are always significant 3. Zeros at the beginning of a number are never significant 4. Zeros at the end of a number and after a decimal point are always significant 5. When a number containing no decimal point has zeros at the end, the zeros are not significant Scientific Notation 1000. = 1.000x10 3 1000 = 1x10 3 Decimals determine the number of sig figs in notation Recognize the number of sig figs and only indicate them in the notation i.e 5240000= 5.24x10 6 Rounding to the correct digit 1. If digit to be dropped is greater than 5, last remaining digit is rounded up 2. If number to be dropped is less than 5, last remaining digit stays the same 3. If number to be dropped is exactly 5, then if the digit to the left og 5 is a. Even, it remains the same b. Odd, it is rounded up Sig Fig Calculations Multiplication and Division -number of significant figures in the answer should be equal to the number of significant figured in the least precise measurement -fewest sigfigs 3.14 x 5.2=16.328 = 16 3.14 x 5.20=16.328 = 16.3 Addition and Subtraction -the answer should have the same number of decimal places as the quantity with the fewest decimal places 3.14+5.2+17.00002= 25.34002= 25.3 Exact Numbers Numbers that come from definitions 12 in= 1ft 60s= 1min Numbers that come from a direct count Number of people in a small room Have no uncertainty Assume they have an infinite number of sig figs Do not affect the number of sig figs in multiplication or division Unit Conversions Also called the Factor Label Method Not all calculations use a specification equation Use units (dimensions) to analyze problem Conversion Factor: -fraction formed from valid equality or equivalence between units -used to switch from one system of measurement and units to another desiredunit conversion factor= givenunit what is a significant figure? There are two kinds of numbers -approximate: weight, height, anything measured, no measurement is perfect -exact: the amount of money in your account, know with certainty when to use sig figs When a measurement is recorded, only those digits that are dependable are written down If you measured the width of a paper with a ruler, you might record 21.7 cm To a mathematician, 21.70 and 21.700 is the same, but to a scientist, 21.700 cm is NOT the same. It means the measurement is accurate to within one thousandth of a cm. Common Pitfalls: Trailing Zeros Zeros at the end of a number and after a decimal point are always significant -these zeros are showing how accurate the measurement or calculations are Zeros at the beginning of a number are never significant (place holders) -they act only to locate the decimal points .1 vs 0.1 Both have the same number of sig figs, however; 0.1 is easier to read Rounding to correct digit 1. if a digit to be dropped is greater than 5, it goes up 2. if the number to be dropped is less than fiver, round down 3. if the number to be dropped is exactly 5, then if the digit to the left is a. even, it stays the same b. odd, it rounds up Unit Conversion Consider the following: 1. what data is given? 2. What quantity do we need? 3. What conversion factors are available to take us from what we are given, to what we need? 1∈¿x 100cm=2.54cm 1m −2 ¿∈ x 2.54x10 m 1 ¿ ¿ e.x convert a person’s height from 68.0 in to cm what data is given? 68.0 in What quantity do we need? Height in cm What conversion factors are available to take us from what we are given, to what we need? 2.54cm= 1 in 1∈¿=173cm ¿ 2.54cm 68.0∈ ❑ x ¿ ¿ The answer must have at least 3 sig figs Specific Gravity Ratio of density of substance to density of water densityof substance Specific gravity= densityof water Unitless Way to avoid having to tabulate
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