Presentation on theme: "Chemistry 101 : Chap. 1 Matter and Measurement"— Presentation transcript:
1 Chemistry 101 : Chap. 1 Matter and Measurement What is Chemistry and Why we study it(2) Classification of Matter(3) Properties of Matter(4) Units of Measurement(5) Uncertainty in Measurement(6) Dimensional Analysis
2 The Study of ChemistryChemistry: The study of the properties of matter and thechanges that matter undergoes. Matter : Physical material of the universeAnything that has mass and occupies space Changes in Matter : Physical or Chemical changesWhy Chemistry? Chemistry is the central science Chemistry is a practical science and has profoundimpact on our daily living
3 Macroscopic vs. Microscopic Macroscopic World : Realm of ordinary-sized object.Things we can see with the naked eye. (Sub)Microscopic World : Realm of atoms and moleculesCarbon nanotube (10-9 m)Chemistry is the science that seeks to understand the propertiesand behavior of matter (macroscopic) by studying the propertiesand behaviors of atoms and molecules (microscopic)
4 Major Divisions in Chemistry Physical Chemistry (CHM321, CHM420) Organic Chemistry (CHM211, CHM212) Inorganic Chemistry (CHM 455, CHM546) Analytical Chemistry (CHM235, CHM435) Biochemistry (CHM365, CHM568)All divisions are interrelated and cannot bestanding alone.
5 Classification of Matter: pure substance vs. mixture Pure Substance: A sample of matter that has distinctproperties and a composition that doesn’t vary from sampleto sample (either element or compound)Elements: A pure substance that cannot bedecomposed into simpler substances. The basic unitof an element is an atom.Nitrogen atomNitrogen moleculesArgon gas (atoms) Nitrogen gas (molecules)
6 Classification of Matter: pure substance vs. mixture Compound : Substances that are composed oftwo or more elements. The basic unit of compound isa moleculeMixture : Combinations of two or more substancesin which each substance retains its own chemical identity.nitrogen atomTwo or more elements(compound)Two or more substances(mixture)hydrogen atomammonium (molecule)
7 Elements At the present time, there are 116 elements Periodic Table of the Elements= H2, N2, O2, F2, Cl2, Br2, I2
9 Compounds Most elements can interact (or react) with other elements to form compoundsExample: Combine hydrogen & oxygen to generate waterOxygen Hydrogen waterHowever, elemental hydrogen and oxygen exist as diatomicmolecules (H2 and O2) in nature.+O H22H2O
10 Mixture Components: The substances making up a mixture Homogeneous Mixture (solution) : Uniformly distributedthroughout. (air, salt solution, sugar solution …)Heterogeneous Mixture : Do not have the samecomposition, properties and appearance throughout.(rock, wood …)Oil on waterAir
12 Classification of Matter Example14 K gold(2) Orange Juice(3) A cup of coffee(4) Mud
13 Separation of MixtureSeparate a mixture into its components by taking advantageof the difference in their propertiesFiltration : Separation is basedon the size of particles in themixture. Filtration is used withheterogeneous mixtures
14 Separation of Mixture Distillation : Separation is based on the boiling points of thecomponents in the mixture.Distillation is typically usedwith homogeneous solutions.Water changes itsstates from gas toliquid
15 Separation of Mixture Chromatography : Separation is based on the solubilitiesof the components in the mixture. It is normally used withhomogeneous mixture.Paper chromatography
16 Classification of Matter: states of matterStates of matter: A sample of matter can have threephysically different states Gas : Indefinite volume and indefinite shape(depends on the volume and shape of its container) Liquid : definite volume, but indefinite shape. Solid : definite volume and definite shapePure substance can have any state dependingon the temperature and pressure
18 Properties of MatterPhysical properties : They can be measured withoutchanging the identity and composition of the substanceEx. color, order, density, boiling point… Chemical properties : They describe the way a substancecan change or reactEx. flammability, solubility, …
19 Physical vs. Chemical Properties Example : Zinc (Zn)silver-grey metalmelting point: 420oCreacts with oxygen toform Zinc oxide (ZnO)density (25oC) = 7.13 g/cm3generates hydrogen whendissolved in sulfuric acid
20 Properties of Matter Extensive properties : Properties that depend on the quantity of a sample.Ex. Volume : + = V1 + V2 = V1 + V2 Intensive properties : Properties that are independenton the quantity of a sampleEx. Temperature : + = T T T
21 Extensive vs. Intensive Properties Example :Boiling/melting point (bp/mp)MassDensityPressure
22 Changes of Matter Physical changes : Phase changes, but it is still H2O (no change in itscomposition)Chemical changes :Aluminum (Al) reacts withBromine (Br2). (A substanceis transformed into a chemicallydifferent substance: AlBr3)
23 Units of Measurement : SI Unit Système International (SI) d’UnitésInternational agreement on the metric units for theuses in science (1960)
24 Units of Measurement : Prefixes Prefixes : They are used to indicate decimal fractionsor multiples of various units.A Megabyte of memory : 106 bytes of memoryFemtochemistry : chemistry that occurs on the time scale of secondcheck out (prof. Zewail’s homepage)
25 Length and Mass Length : 1 meter (m) = 100 cm Mass : 1 kilogram (kg) = 1000 gMetric to English conversion1 m = yard1 cm = inch1 kg = lbCheck outNOTE: Mass and weight are not the same thing. Mass is an intrinsicproperty of matter, but weight depends on the gravity.
26 Temperature Water freezing Water boiling Celsius scale (oC) 0 100 Fahrenheit scale (oF)oC = 5/9 (oF 32) oF = 9/5(oC) + 32Kelvin : K = oC (exact)Absolute zero temperature : 0 K = oCThe lowest attainable temperature in our universe
27 Temperature (98.6 oF 32)5/9 = 37 oC 37 oC + 273.15 = 310.15 K William Thomson Kelvin( )“On an Absolute Thermometric Scale”Philosophical Magazine, vol. 1pp (1848)(98.6 oF 32)5/9 = 37 oC37 oC = K
28 Derived Units Use the defining equation for the quantity of interest and substitute the appropriate SI units Volume: abc = (length)3 = m3abcIn chemistry, we normally usesmaller units.Liter : (10 cm)3 = 1 L = 1 dm3 = 10-3 m31 gal = 3.8 L(2) Milliliter = 1 mL = 10-3 L = 1 cm3 = 1 cc
29 Derived Units Density : The amount of mass in a unit volume of substanceSI unit ofdensity In chemistry, we typicallyuse g/mL = g/cm3 = g/cc Density depends ontemperature Don’t be confused aboutdensity and weight
30 Density, Volume and Mass (1) 1.00 102 g of mercury occupies a volume of 7.36 cm3. What isthe density of mercury?(2) The density of liquid methanol is g/mL. What is the volumeof 65.0 g of liquid methanol?(3) The density of gold is g/cm3. What is the mass in gram of acube of gold if the length of the cube is 2.00 cm?
31 Uncertainty in Measurement We need to distinguish two different types ofnumber in science Exact Number : Defined number1 dozen = 12, 1 m = 100 cmCounted numberThere are 120 students in the class. Inexact Number : Numbers from measurement(human errors, machine errors..)
32 Precision and Accuracy Precision : How closely individual measurements agreewith one another. Accuracy : How closely individual measurements agreewith the correct or “true” value.good precisionpoor accuracygood precisiongood accuracypoor precisionpoor accuracy
33 Significant FiguresMeasured quantities are generally reported in such away that only the last digit is uncertain.mass of a dime = gUncertain. Could be 6 or 4…(2) Sometimes, sign is used to specify the uncertainty.mass of a dime = gSignificant Figures : All digits of a measured quantity,including the uncertain one.g 5 significant figures
34 Rules for Significant Figures All non-zero digits are significant(2) Zeros at the beginning of a number are never significant count the digits starting with the first non-zero digithas TWO significant figures(3) Zeros between non-zero digits are significant has THREE significant figures(4) Zeros at the end of a number are significant. has FOUR significant figures2060 has FOUR significant figures2.06 x 103 has THREE significant figures
35 Significant Figures in Calculation The number with the fewest number of significant figureslimits the certainty of the calculated quantity.Multiplication & Division : The final answer can haveno more significant figures than the fewest number ofsignificant figures in any number in the problem. Addition & Subtraction : The final answer can haveno more decimal places than the fewest number ofdecimal places in any number in the problem
36 Significant Figures in Calculation Example 1: Area of a rectangle whose measured edgelengths are cm and 5.2 cmArea = (6.221 cm) x (5.2 cm) = cm2 =Only 2 significantfiguresInclude only 2significant figuresExample 2 : Addition of three measured numbers20.421.322+ 83.1
37 Significant Figures in Calculation When calculation involves multiple steps…Retain at least one more extra digit (past the numberof significant figure) in each step When you use a calculator…Enter the numbers one after another (withoutworrying about significant figures) and roundingonly the final answer
39 Dimensional AnalysisWe carry units through all calculations. Units behavelike numbers: they are multiplied together, dividedinto each other, or canceled.Example: How many inches are in 10 cm?Correct WrongAdvantages of dimensional analysis(1) It ensures that your answer has the correct unit(2) It makes it easier to find out possible errors
40 Unit Conversion Example: The speed of N2 in air at 25 oC is 515 m/s. Conversion factorExample: The speed of N2 in air at 25 oC is 515 m/s.Convert the speed into mile/hour
41 Unit Conversion Example: The density of water is 1.00 g/mL. What is the mass 1.00 gal of water in grams?
42 An exampleThe density of gold is g/cm3. If 2.00 g of gold wire has 0.12 mmradius, how long the wire is?