Pack 1 - CHEM 205 - F24 - MBM.pdf
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© CR, MBM 2024 GENERAL CHEMISTRY I - Chem 205 Week 1: Sept. 5, 2024 (Lec. 52) Topics: Kotz 11th: Ch.1 + Let’s review quantitation sections OpenStax: Ch.1 Professor: Dr. Marek...
© CR, MBM 2024 GENERAL CHEMISTRY I - Chem 205 Week 1: Sept. 5, 2024 (Lec. 52) Topics: Kotz 11th: Ch.1 + Let’s review quantitation sections OpenStax: Ch.1 Professor: Dr. Marek Majewski, [email protected] Office hours: TBD WHY STUDY CHEMISTRY ? learn how substances tend to behave and why learn to understand real-world phenomena BUILD SKILLS: ▪ learn to think on multiple levels (cause & effect) ▪ learn to apply knowledge & attack problems © CR, MBM 2024 Chemistry - think small to understand the big picture microscopic Particulate macroscopic (not small enough) (nanoscopic) Graphite: slippery (= pencil lead, lubricant…) WHY? ▪ layered structure of carbon atoms ▪ layers can slide ! https://physicsopenlab.org/2018/01/31/graphite-structure/ How is behaviour related to composition? ▪ What are the substance’s fundamental building blocks? ▪ How they are arranged? Can we manipulate composition to get results we want? ▪ Pharmaceuticals, plastics, preservatives, paints, etc… (3) Kotz Fig. 2.8, p. 80 © CR, MBM 2024 Sustainability & Green Chemistry (Kotz Ch.1 sect.1.2) Green chemistry principles to live by: (much of this applies to everyday life…) PLAN AHEAD: Prevent waste rather than cleaning it up afterwards. BE EFFICIENT: Design synthetic methods to maximize the incorporation of starting materials into the final product. USE LESS ENERGY: Perform reactions at ambient temperatures and pressures, to minimize cost & environmental impact of energy usage. BE CAUTIOUS: Choose substances that minimize the potential for chemical accidents, including releases, explosions and fires. LIMIT TOXICITY: Design synthetic methods to use & generate substances that possess little/no toxicity to human health or the environment. Design chemical products to function effectively while still reducing toxicity. GO RENEWABLE: Choose renewable raw materials whenever technically and economically practical. GO BIODEGRADABLE: Design chemical products so that, at the end of their function, they do not persist in the environment or break down into dangerous products. (4) https://www.acs.org/content/acs/en/greenchemistry/principles/12-principles-of-green-chemistry.html © CR, MBM 2024 1ST: WHAT HAPPENS 2ND: UNDERSTANDING WHY (practical) (theoretical) TIMELINE OF TOPICS IN CHEM205 Making measurements LR & & Classifying matter Ch.1 Atoms & elements Ch.2 Molecules, ions & compounds Typical reactions Understanding how molecules are Ch.3 that occur in water put together & how this affects the Ch.8 properties of substances Chemical equations & reaction outcomes Ch.4 How to think realistically Ch.6 about atoms start this Why different elements on your own Ch.7 have different properties Ch.10 Understanding the behaviour of gases (5) © CR, MBM 2024 Ch.1: Reviewing the basic concepts of chemistry “Let’s review” quantitation (after Ch.1 in text) Chapter Goals - Study Checklist: 1 Units of measurement ❑ Use scientific notation, metric units & 2 Precision, accuracy & exp’tal error significant figures correctly 3-6 Math & problem-solving in chemistry ❑ Explain precision vs accuracy, & calculate error vs deviation 1.1 Chemistry & its methods ❑ Apply dimensional analysis & 1.2 Sustainability & green chemistry problem-solving strategies 1.3 Classifying matter ❑ Explain the scientific method & 1.4 Elements hypothesis vs law vs theory 1.5 Compounds ❑ Use chemistry’s viewpoints: 1.6 Properties and changes macroscopic, microscopic, symbolic 1.7 Energy: some basic principles ❑ Classify matter ❑ Recognize elements, atoms, compounds, molecules Order in lectures (see slide titles): ❑ Recognize physical vs chemical Start with: quantitative aspects properties & identify physical vs (1.1, “LR” 1-6 & 1.6) chemical change Next : qualitative aspects ❑ Apply kinetic-molecular theory to (1.3-1.7) properties of matter & explain how it relates to energy (6) © CR, MBM 2024 1.1 The Scientific Method ▪ Qualitative / Quantitative OBSERVATION ▪ Tentative explanation HYPOTHESIS ▪ Systematic, controlled EXPERIMENT observations / measurements ▪ Verbal / mathematical description of WHAT HAPPENS Law ▪ Model proposed to EXPLAIN WHY Theory (model) the behaviour occurs Modify as needed Experiment From: Chemistry – Principles, Patterns & Applications, (7) by B.Averill & P. Eldredge; Pearson; 2007. © CR, MBM 2024 Reporting results to other scientists (including teachers) ▪ Experimental results should be reproducible. ▪ Results should be reported in sufficient detail that they can be used or reproduced by others. student lab results: in notebooks & reports research results: in the scientific literature ▪ Conclusions should be reasonable & unbiased. ▪ Credit should be given where it is due. (Images from: Kotz 8th Ed.) (8) © CR, MBM 2024 “Let’s review”: Units of measurement & using numerical information OBSERVING PHYSICAL & CHEMICAL CHANGES: 1. Qualitative observations: descriptive 2. Quantitative observations: numerical ▪ A measurement = a quantitative observation consisting of TWO parts NUMBER + UNIT 20 grams (g) 6.63×10−34 Joule seconds (Js) 6.02×1023 atoms 110 students (9) A NUMBER WITHOUT A UNIT IS MEANINGLESS! © CR, MBM 2024 SI (metric) system: a decimal-based system of units base units: gram (g), meter (m), Liter (L), second (s)… use prefixes to denote larger/smaller than base units From Zumdahl’s Chemistry 6th Ed. (see Kotz Let’s Review Table 2) (10) © CR, MBM 2024 Quantitative observations = measuring things Properties with numerical values do not necessarily reflect the sample’s size. Intrinsic properties vs. extrinsic properties (intensive) (extensive) Characteristics of the Properties that depend on substance itself, the quantity of substance not the quantity present: Density Weight Melting point Volume Boiling point Length, width, height… Viscosity etc… Is temperature an intrinsic or extrinsic property? (11) © CR, MBM 2024 Scientific temperature scales Celsius Kelvin (centigrade) (absolute) Celsius & Kelvin units are same size, but OFFSET: WATER BOILS TK = TC x 1 K + 273.15 K 1C Absolute zero = 0 K = ____ C Liquid N2 boils at 77 K = ____ C Room temperature = ___ K = 25 C CLICKER Q: At normal pressures, solid CO2 (dry ice) WATER does not melt, but instead undergoes FREEZES sublimation above −78.51°C. What is this temperature in Kelvins? A. −351.66 K B. 78.51 K C. 194.64 K (12) © CR, MBM 2024 MEASUREMENTS: Uncertainty & Significant Figures ▪ Digits unambiguously read off a scale are certain (= known exactly) ▪ The last digit reported is always estimated & is called uncertain. ▪ Important: estimated digit is uncertain, but is significant. Analog scale: you estimate by reading between gradations Digital scale: machine estimates last digit mL Using scales of differing precision 1.0- 0.6 m ± 0.1 0.5 - 0.65 m ± 0.01 0.648 m ± 0.001 From Addison-Wesley’s Chemistry (highschool text…) Zumdahl Chemistry, 7th Ed. Imagine a tiny measuring stick 1 mm long marked in 100th gradations. - size: 10−3 m long (order of magnitude of measurements) - increments: 10−5 m (0.01×10−3) (last digit will be estimated b/w markings) - range: 0.000×10−3 – 1.000×10−3m (precision level: increment + 1 digit) A measurement made with this: 0.328 mm = 0.328×10−3 m (± 0.001×10−3) - (13) © CR, MBM 2024 Where does uncertainty come from? “SOURCES OF ERROR” ▪ Random Error ▪ Systematic Error (Indeterminate Error) (Determinate Error) Measurement has an equal Occurs in the same direction probability of being high or low. each time (too high, too low). Usually unavoidable. Often results from poor technique or poor expt design Magnitude determined by: Magnitude determined by: - size of scale’s divisions - size of scale’s divisions - worker’s attention to detail Direction determined by: - random: varies each time Direction determined by: last digit is estimated - calibration of instrument e.g., uncertainties in lengths e.g., bathroom scale offset… & volumes on last slide… (14) © CR, MBM 2024 Accuracy vs. precision: describing your data ▪ Accuracy: refers to the agreement of a particular value with the true value ACCURATE (or accepted value) but imprecise Relative error (often as %) = Average exp’tal value – true value true value ▪ Precision: refers to the PRECISE degree of agreement among but inaccurate several measurements of the same quantity. Deviation (for each measurement) = ACCURATE Exp’tal measurement – average value and PRECISE Standard deviation? see Kotz 11th p.40 see Kotz 11th LR Fig 1R.5 (15) © CR, MBM 2024 Comparing data sets: precision vs. accuracy Since the year 2000, the penny weighs 2.35 g. Data: http://en.wikipedia.org/wiki/Penny_(Canadian_coin) Balance images: http://www.coleparmer.ca/catalog “Top-loading” balance: Digital “analytical” balance: Penny Mass (g).Dev. (g) Penny Mass (g).Dev. (g) 1 2.34 0.00 1 2.3215 0.0014 2 2.33 0.01 2 2.3188 0.0013 3 2.35 0.01 3 2.3206 0.0005 4 2.33 0.01 4 2.3192 0.0009 5 2.35 0.01 5 2.3203 0.0002 Avg 2.34 0.01 More precise → Avg 2.3201 0.0009 % rel. error = −0.4 % More accurate % rel. error = −1.27 % Observed – Accepted value If numerator as % relative error = × 100 absolute value, say Accepted value too high vs too low. (16)Which balance was improperly calibrated, causing systematic error? © CR, MBM 2024 Significant Figures reveal precision of measuring method CLICKER Q: Reporting measurements with correct SF (“sig.figs”) Imagine you weigh 25.7172 g of NaCl crystals on a A. 2 SF: 26 g electronic balance known to have a precision of ± 1 B. 3 SF: 25.7 g mg (i.e., uncertainty in the mg digit). C. 4 SF: 25.72 g How many significant figures should be D. 5 SF: 25.717 g reported for this measurement? E. 6 SF: 25.7172 g MEMORIZE: Rules for counting SF in a given number (Kotz pp. 43-46) ▪ Non-zero integers always count as sig.figs. 345 m has 3 SF ▪ Captive zeros always count as sig.figs. 16.07 mL has 4 SF ▪ Leading zeros do NOT count as sig.figs; 0.0486 g has 3 SF they indicate order of magnitude. = 4.86×10−2 ▪ Trailing zeros are significant IF before or after a decimal point; they indicate the measurement lay exactly on a gradation line. 4200. L = 4.200×103 has 4 SF vs 4200 L = 4.2×103 has 2 SF Exact numbers (defined quantities, reference values, # counted): error-free (infinite # SF): 1 mL = 1 cm3, oxygen 15.996 g/mol, 3 eggs (17) © CR, MBM 2024 Rules for Sig. Figs in Mathematical Operations ▪ Rounding: Round up if 1st non-significant figure is ≥ 5 ▪ Addition and Subtraction: # sig. figs in result is limited by the number of decimal places in least precise measurement (piece of data) used in calculation keep lowest # decimal places in answer 6.8 ▪ Picture lining up decimals of measured #s (written at same + 11.954 order of magnitude). 18.754 ? ✓ = 18.8 (3 SF) reveals least precise # used, & dominates answer’s uncertainty. ▪ Multiplication and Division: # sig. figs in result is same as the number of sig. figs in least precise measurement used: 6.38 2.0 = 12.76 ? ▪ Unfortunately, there is no simple way to ✓ = 13 (2 SF) visualize why this rule is used. THE GOAL: to make sure our numerical results honestly reflect (18) the level of uncertainty in the raw data used. © CR, MBM 2024 Multistep calculations: avoid rounding error by rounding only at end ▪ Follow order of operations: ( ) 1st, then //exponents, then +/- ▪ For EACH operation: apply matching SF rule, BUT: underline the last significant figure in # keep 1-2 extra SFs for next step ▪ At very last step: round off to correct # SFs for last step CLICKER Q: Applying SF rules to realistic data.Mass (by difference, same scale). = 1832.0 g – 926.2 g Volume (perfect sphere) 4/ (3.05 cm)3 3 After 1st 2 steps: = 905.8 g. sample of (not yet rounded) 4/ (3.14159…)(28.3726 cm3) unknown 3 density After rest of steps: = 7.621566 g/cm3 (not yet rounded) How should the density A. 7.6216 g/cm3 value be reported? B. 7.622 g/cm3 (i.e., appropriate SFs…) C. 7.62 g/cm3 (19) D. 7.6 g/cm3 © CR, MBM 2024 (1.6) DENSITY: a quantifiable d = mass physical property of substances volume How heavy is a given volume of a substance? Depends on: 1.) mass of individual particles (atoms/ions/molecules) 2.) how tightly packed together they are in the structure = a characteristic, intrinsic, physical property of any pure substance (details on pure substances later…) (20) © CR, MBM 2024 A very useful intrinsic (characteristic) property: DENSITY IS AN ‘IDENTIFICATION TAG’ (21) Images from: Kotz 8th Ed. Table from: Chemistry, 6th Ed., by S. Zumdahl & S. Zumdahl; Houghton Mifflin, 2003. ON YOUR OWN: Determination of a metal’s density © CR, MBM 2024 An irregularly shaped piece of silver-coloured metal with a mass of 142.45 g is immersed in water in a graduated cylinder (shown). Determine the identity of the metal. A. Magnesium, Mg (1.74 g·cm-3) B. Aluminum, Al (2.70 g·cm-3) C. Iron, Fe (7.87 g·cm-3) D. Silver, Ag (10.5 g·cm-3) E. Lead, Pb (11.3 g·cm-3) (22) modified from Kotz 9th LR #63 © CR, MBM 2024 CLICKER Q: Drawing reasonable conclusions from data There are 5 hydrocarbons with formula C6H14 with different connectivity of atoms (= “isomers”). All 5 are liquids at room temperature, but they have slightly different densities. You have a pure sample of ONE of them. Hydrocarbon Density Your 1st 2nd isomer (C6H14) (g/cm3) sample A 2,2-dimethylbutane 0.6600 Mass 3.2745 g 3.2745 g B 2-methylpentane 0.6532 uncertainty C 1-methylpentane 0.6645 Volume 5.0 cm3 4.95 cm3 D hexane 0.6616 uncertainty E 3,3-dimethylbutane 0.6485 Density uncertainty To identify the isomer by its density: ▪ you measure a volume of sample using the graduated cylinder sitting on your lab bench, then measure its mass with an analytical balance ▪ your partner measures a second aliquot of sample with a pipette (coincidentally identical mass, to demonstrate the point here) Within the limits of your experimental error, what do you conclude…? using the 1st volume measurement: using the 2nd volume measurement: & about apparatus choices? (23) © CR, MBM 2024 Problem solving – interpret, plan, execute 1. Interpret the question. ▪ Determine what the problem is asking. 2. Develop a plan of attack. ▪ Identify key principles. ▪ Sketch diagram / write chemical equation. ▪ Organize information: known vs. unknown; + units. ▪ Break problem into simpler ones – take logical steps. 3. Execute the plan. ▪ Show all units – do they yield desired units at end ? ▪ Don’t skip steps (& don’t round off prematurely). 4. Check your answer. ▪ Common sense – is it a reasonable number ? ▪ Verify number of significant figures. (24) © CR, MBM 2024 What drug dose was given? Procaine hydrochloride (novocaine) is an anesthetic often used to deaden pain during dental surgery. The compound is packaged as a 10.0% solution (by mass; d = 1.0 g/mL) in water. a) If your dentist injects 0.50 mL of this solution, what mass of procaine hydrochloride (in mg) is injected? b) If 1 g of pure procaine hydrochloride contains 2.47×1021 molecules, how many molecules of the anesthetic do you receive? Modified from Kotz 9th L.R. #39. (25) ANS: 50. mg = 5.0×101 mg (2 SF) = 1.2×1020 molecules © CR, MBM 2024 ON YOUR OWN: Sterling silver - what is its composition? Sterling silver is a solid solution or “alloy” of silver (Ag) and copper (Cu). If a piece of a sterling silver necklace has a mass of 105.0 g and a volume of 10.12 mL, calculate the mass percent of silver in the necklace. Assume that the volume of silver present plus the volume of copper present equals the total volume. DATA: dAg = 10.5 g/cm3 dCu = 8.96 g/cm3 Hint: build a set of 2 equations & 2 unknowns (algebra practice!) (26) Zumdahl’s Chemistry, 7th Ed., Ch.1 #87 ANS: 93.0% Ag (& rest Cu) © CR, MBM 2024 Qualitative observation = describing things The different levels of chemical thinking (Kotz Fig.1.6) (27) © CR, MBM 2024 1.3 Classifying matter: States of matter Kotz Fig. 1.5 (a particulate view) BROMINE (Br2) in its 3 STATES: SOLIDS GASES ▪ rigid shape, ▪ expand to fixed volume. fill their ▪ external shape can LIQUIDS container. reflect particles’ ▪ fluid shape, but fixed ▪ behaviour arrangement. volume. very well ▪ behaviour is ▪ behaviour is not well understood reasonably well understood (& simple). understood. (i.e., complicated). See Ch.10 (28) © CR, MBM 2024 1.4 Elements (details? Ch. 2, 6, 7) CHEMICAL ELEMENT: ▪ pure substance that cannot be subdivided into any other substances via physical or chemical methods (details about methods soon…) ▪ building blocks: composed of only ONE kind of atom Kotz Fig.1.11 (29) Hg(l) S(s) Cu(s) Fe(s) Al(s) (29) © CR, MBM 2024 1.5 Compounds (details? Ch. 2, 8) COMPOUND: ▪ pure substance that requires chemical means to be further subdivided ▪ cannot separate into parent elements via physical separation methods ▪ building blocks: composed of ≥ 2 elements’ atoms/ions in a fixed ratio Fixed composition: specific proportions of elements, represented by… 1) chemical formula = atom-to-atom ratio Water: H2O 2) percent composition In 100 g of water: = % each element by mass 11.2 g due to H atoms, 88.8 g to O atoms (as part of molecules, not free atoms) i.e., 11.19% H & 88.81% O by mass Characteristic properties: different from parent elements Water: H2O Hydrogen: H2 Oxygen: O2 Non-flammable vs. Highly flammable Combustion-supporting liquid gas gas (30) © CR, MBM 2024 Chemical means are required to break down compounds into their constituent elements “Redox” reactions Oxygen: Hydrogen: (see Ch.4) O2 H2 e.g., Electrolysis: pass high current through liquid water to decompose it: 2 H2O(l) → 2 H2(g) + O2(g) SIMILARLY: pass high current through molten salt to decompose it: 2 NaCl(l) → 2 Na(s) + Cl2(g) Water: H2O Kotz p. 12 (31) © CR, MBM 2024 Building blocks for compounds = smallest group of atoms / ions that retains BOTH the composition & characteristics of the compound COVALENT COMPOUNDS IONIC COMPOUNDS MOLECULE = atoms bonded IONS = charged (+,-) atoms together into a discrete unit or groups of atoms, which pack in ratios that give Water neutral combinations H 2O Common salt NaCl Caffeine C8H10N4O2 Kotz Fig.1.2 (32) © CR, MBM 2024 CLICKER Q: identify substance type by its building block The figures below represent four different samples of gas-phase matter. Which one represents a mixture of two elements ? (33) © CR, MBM 2024 Matter consists of atoms & molecules (particles!) in constant motion. 1.7 Energy: some basic principles (more in Chem 206) ▪ Energy can be classified as Potential or Kinetic ▪ Potential energy = energy associated with position, including… gravitational E: an object held at a height, waterfalls. chemical energy: energy stored in molecules, due to bonds between atoms electrostatic E: energy due to attractions between charged or partially charged particles nuclear energy: energy associated with attractions between nuclear particles (released via fission, fusion) ▪ Kinetic energy = energy associated with motion, including… mechanical energy: movement of a macrosopic object (e.g., ball) thermal energy: motion at the particulate level electrical energy: movement of electrons in a conductor acoustic energy: compression-type wave motion (34) © CR, MBM 2024 Kinetic Molecular Theory: Matter consists of particles in constant motion. Kinetic energy Temp. i.e., higher temperature faster motion ▪ Between particles: forces of attraction (details in Chem 206)… ▪ Low temperatures: matter usually solid WHY? K.E. is low attractive forces seem large ▪ Higher temperatures: change to liquid…or gas… WHY? Higher K.E. can overcome attractions (35) © CR, MBM 2024 Understanding why density changes with T (see 1.6) FOR MOST SUBSTANCES: density as temperature WHY? ▪ when particles’ kinetic energy decreases (i.e., at lower T), attractive forces between particles are more significant particles move closer together volume decreases Must specify temperature when discussing: density volume (36) © CR, MBM 2024 Water ice is unusual: most solids sink in their liquids H2O(s) is less dense than Temperature Density of H2O H2O(l) at same temp… (°C) (g/mL) 0 (solid) 0.917. WHY? 0 (liquid) 0.99984 When locked in ideal 2 0.99994 geometry for interaction (as 4 0.99997 in solid), H2O molecules are 10 0.99970 a bit farther apart than in 25 0.99707 liquid! 100 0.95836 Most dense at 4°C SOLID (ice) LIQUID (water) From Zumdahl’s Chemistry 6th Ed. (37) © CR, MBM 2024 Phase changes = changes of state ▪ Physical change: change in organization of particles, NOT composition ▪ Temperatures at which changes occur are characteristic properties E.g., bromine: m.p. −7.2C, b.p. +58.8C When particles move closer GAS together: energy released as heat. When particles LIQUID are forced farther apart: energy input required. SOLID (38) Making observations: always describe before AND after (38) © CR, MBM 2024 Qualitative observation = describing things 1.6 Physical properties see Table 1.1 How can we identify a substance (if it’s pure)? Can observe & describe…without changing its composition ▪ Colour, odour ▪ State of matter: Gas? Liquid? Solid? ▪ Appearance: Shape? Powdered? Crystalline? Transparent? ▪ Melting point, boiling point, sublimation ability ▪ Solubility: How much will dissolve? In what will it dissolve? ▪ Electrical conductivity: conductor vs. insulator? ▪ Malleability: easily deformed? ▪ Ductility: easily drawn into a wire? ▪ Magnetic properties: attracted to magnetic field? ▪ Viscosity: for liquids: thick or thin? Does it flow easily? ▪ Density: mass per unit volume (39) © CR, MBM 2024 CLICKER Q: describing properties A large block of crystalline table salt (sodium chloride, NaCl) is shown. Which choice correctly describes the appearance of this substance? A. Clear & colourless B. Opaque & colourless C. Translucent & colourless D. Transparent & colourless E. Both A & D Other physical properties of NaCl include: brittle water-soluble conductive when melted or dissolved Kotz Fig.1.2 (40) © CR, MBM 2024 Classifying matter: mixtures vs. pure substances Kotz Fig.1.7 Matter: solid, liquid or gas anything that fills space & has mass Heterogeneous matter: PHYSICALLY Homogeneous matter: SEPARABLE non-uniform in appearance INTO uniform appearance always a mixture of substances but might be a mixture Solution: PHYSICALLY Pure substance: SEPARABLE uniform mixture of substances INTO fixed composition widely variable compositions cannot be further purified REACT Element: CHEMICALLY Compound: TO FORM cannot be subdivided via cannot be subdivided via chemical OR physical means CHEMICALLY physical methods SEPARABLE elements in fixed ratios INTO (41) © CR, MBM 2024 Separating heterogeneous mixtures: by filtration (a physical method) filter Kotz Fig. 1.9 filter solid on filter industrial scale heterogeneous homogeneous liquid - solid liquid filtrate → to further purify: mixture …evaporate solvent & collect residue (42) © CR, MBM 2024 Separating homogeneous mixtures: by distillation (a physical method) A mixture of volatile liquids, or perhaps The most volatile liquid volatile liquid(s) distills over first. and involatile This flask is changed to dissolved solids. collect separate fractions. Image from Zumdahl (43) © CR, MBM 2024 Separating homogeneous mixtures: by chromatography (a physical method) ▪ PURPOSE: to determine how many components are in mixture, to test purity, or before attempting large scale separation Images ▪ Analyte: a mixture of coloured dyes (black ink) from Zumdahl ▪ Stationary Phase: filter paper (porous paper) ▪ Mobile phase: probably a mixture of water and alcohol (44) © CR, MBM 2024 CLICKER Q: separating a mixture The beaker contains a solution of a nonvolatile blue solid, copper sulfate (CuSO4), dissolved in water. Which method below would separate the mixture into its two components, such that you would end up with a pure sample of each substance? A. Distillation B. Filtration C. Chromatography D. Sublimation (45) © CR, MBM 2024 1.6 Physical change vs. chemical change Change in organization Change in composition of atoms/molecules/ions of atoms/molecules/ions WHY: WHY: Change in interactions Rearrangement of bonds between molecules between atoms/ions Identity of substance(s) Identity of substance(s) UNCHANGED CHANGED melting butter burning butter dissolving sugar in water digesting sugar boiling water reacting water with Na(s) BOTH often involve transfers of energy: release (or absorption) of HEAT or LIGHT (47) © CR, MBM 2024 Chemical change = change in composition (identity) ▪ Chemical reactions involve REARRANGEMENT of bonds between atoms…but not net loss/gain of atoms Macroscopic view: Particulate view: Symbolic view: 2 H2(g) + O2(g) 2 H2O(g) Chemical Reactants Products change (48) Kotz Fig. 1.16 © CR, MBM 2024 Chemical properties: rxns typical of a substance Many substances react with oxygen and/or water: ▪ Combustion -- of wood, gasoline “organic materials” ▪ Rusting -- of iron ▪ Tarnishing -- of silver (is not an example!!) ▪ Hardening -- of cement ▪ Violent reaction with water E.g., potassium metal → The Royal Institution on YouTube https://www.youtube.com/watch?v=E7VWjHTDrKo (49) Making observations: Always describe before AND after © CR, MBM 2024 CLICKER Q: physical vs chemical change Consider the following statements about sulfur (S), a yellow non-metallic element. 1) Sulfur is produced commercially by injecting steam into underground sulfur deposits to melt it. Kotz Fig. 2.10 2) It is then carried by the steam to the surface, where the sulfur separates from the water after cooling. 3) Sulfur burns in oxygen to form a choking gas, SO2, which reacts with water to form acid rain. Which statements describe(s) a chemical reaction ? A. Statement 2 only. B. Statement 3 only. C. Statements 1 & 2. D. Statements 2 & 3. E. All of them. (50) © CR, MBM 2024 CLICKER Q: understanding a common observation A student slowly heats some water (H2O) in a beaker. When the water reaches 30 C, bubbles begin to form on the walls of the beaker and eventually float to the surface. At 100 C, bubbles form rapidly throughout the water as it boils. Which option (A-E) describes the composition of the bubbles at the two temperatures? At 30 °C AND At 100 °C A water vapour H2O (g) hydrogen H2 (g) & oxygen O2 (g) B water vapour H2O (g) hydroxide ion OH– (g) & hydrogen ion H+ (g) C air (N2 & O2 gases) water vapour H2O (g) & a little H2O (g) D water vapour H2O (g) air (N2 & O2 gases) & a little H2O (g) E carbon monoxide CO (g) carbon dioxide, CO2 (g) & oxygen O2 (g) Physical PHASE CHANGE: H2O(l) change H2O(g) (a physical change) Water Water vapour (steam) (51) © CR, MBM 2024 ASSIGNED READINGS ▪ BEFORE NEXT CLASS: Read Ch. 1 & “Let’s review” sections & work on exercises & learn to use your calculator properly (e.g., scientific notation) ▪ LAB-TUTORIAL CHECK-IN week of Sept. 16 WHICH GROUP? Find out at lab-tutorial check-in. ON YOUR OWN: learn/practice Ch.1 concepts/terms practice L.R. concepts/calculations ▪ CHEM 101 SEMINARS: Sept. 17, 19, 23, 21:00, Zoom Make sure to register at the links provided in the syllabus (52)
