3.1 properties of matter 3.2 changes in matter 3.3 mixtures of matter
DESCRIPTION
Chapt 3 Matter – Properties & Change. 3.1 Properties of Matter 3.2 Changes in Matter 3.3 Mixtures of Matter 3.4 Elements and Compounds (for treatment of simple hydrocarbons and isomers, see ppt Section 21.4 & Related – Isomers). Section 3.1 Properties of Matter. - PowerPoint PPT PresentationTRANSCRIPT
3.1 Properties of Matter
3.2 Changes in Matter
3.3 Mixtures of Matter
3.4 Elements and Compounds (for treatment of simple hydrocarbons and isomers, see ppt Section 21.4 & Related – Isomers)
Chapt 3 Matter – Properties & Change
Section 3.1 Properties of Matter
• Identify the characteristics of a substance.
• Distinguish between physical and chemical properties and changes and be able to give examples of each.
• Distinguish between intensive and extensive physical properties and be able to give examples of each type.
• Differentiate among the physical states of matter; know the meaning of the term “vapor”.
Most common substances exist as solids, liquids, and gases, which have diverse physical and chemical properties.
Section 3.1 Properties of Matter
Key Concepts
• The three common states of matter are solid, liquid, and gas. Physical properties can be observed without altering a substance’s composition.
• Chemical properties describe a substance’s ability to combine with or change into one or more new substances.
• External conditions can affect both physical and chemical properties.
Substance
Matter that has a uniform and unchanging composition (aka pure substance)
• Copper (Cu – an element)• Salt (sodium chloride, NaCl)• Dionized water (H2O)
Any matter that is not a pure substance is a mixture – see section 3.3
• Tap water (has dissolved minerals)
States of MatterSolid - Definite shape and volume
Liquid - Flows, constant V, takes shape of its container
Gas - Conforms to and fills entire volume of container
Vapor – gaseous state of room temperature solid/liquid
Physical PropertiesCan be observed or measured without changing samples composition
• Density Color Luster Hardness• Conductivity Melting/boiling points
Physical Properties of Common Substances – Table 3.1
Extensive/Intensive PropertiesExtensive – dependent upon amount of substance present
MassLengthVolume
Intensive – not dependent upon amountDensityPressureTemperature
Ignore book example re: scent & spices
Chemical Property
Ability of a substance to combine with or change into one or more other substances
Properties of Cu – Table 3.2
Note distinctions between physical and chemical properties
PracticeProblem 3 page 75
Classify each of the following as [being related to] a physical or a chemical property:
chem
chem
phys
phys
phys
a. Iron and oxygen form rust
b. Iron is more dense than aluminum
c. Magnesium burns when ignited
d. Oil and water don’t mix
e. Mercury melts at 39 C
Chapt 3 Matter – Properties & Change
3.1 Properties of Matter
3.2 Changes in Matter
3.3 Mixtures of Matter
3.4 Elements and Compounds (for treatment of simple hydrocarbons and isomers, see ppt Section 21.4 & Related – Isomers)
Section 3.2 Changes in Matter
• Define physical change and list several common physical changes.
• Define chemical change and list several indications that a chemical change has taken place.
• Apply the law of conservation of mass to chemical reactions.
Matter can undergo physical and chemical changes.
Section 3.2 Changes in Matter
Key Concepts
• A physical change alters the physical properties of a substance without changing its composition. A chemical change, also known as a chemical reaction, involves a change in a substance’s composition.
• In a chemical reaction, reactants form products.
• The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction; it is conserved.
massreactants = massproducts
Physical Properties and ChangesChanges don’t alter chemical nature
Changes in shape from applied mechanical forces• Cut, bend, crumple
Phase changes• Melting, boiling, condensation, freezing• Melting and boiling points (see table 3.1)
are intensive physical properties useful in identifying a substance
Chemical ChangesIn a chemical change (reaction), reactants (R) form products (P)
R P
New Substances Created• Rusting – Iron (R) to iron oxide (P)• Fermentation – sugar (R) to
alcohol (P)• Combustion – methane (R) to CO2
(P) and H2O (P)
Evidence of Chemical Change
Rusting; properties that change include:
Color: metallic grey brownish orange
Attracted to magnet: yes no
Chemical reaction always produces a change in properties
Conservation of MassMass is neither created or destroyed in a chemical reaction; it is conserved
Mass reactants = Mass products
Lavoisier (1743-1794) credited with concept; studied thermal composition of mercury (II) oxide to mercury & oxygen
Proof of it depended on development of analytical balance capable of detecting small mass changes
Thermal Decomposition of HgO
2HgO(s) 2Hg(l) + O2(g)
Sum of masses of liquid mercury and gaseous oxygen products equal to original mass of mercury(II) oxide solid
Conservation of Mass
2HgO(s) 2Hg(l) + O2(g)
Example problem 3.1 page 78
10.00 g HgO heated to produce 9.26 g Hg
Mass of oxygen formed in reaction?Knowns: mHgO = 10.00 g mHg = 9.26 g
Unknown: mO2 ?
mreactants = mproducts Law of Conservation of Mass
mHgO = mHg + mO2 mO2 = mHgO mHg
mO2 = 10.0 g 9.26 g = 0.74 g of oxygen
PracticeConservation of mass
Problems 5 – 9 page 78
Problems 13(a-b) page 79
Problems 50 – 55 pages 94 - 95
3.1 Properties of Matter
3.2 Changes in Matter
3.3 Mixtures of Matter
3.4 Elements and Compounds (for treatment of simple hydrocarbons and isomers, see ppt Section 21.4 & Related – Isomers)
Chapt 3 Matter – Properties & Change
Section 3.3 Mixtures of Matter
• Define and distinguish between substances and mixtures.
• Define and distinguish between homogeneous and heterogeneous mixtures and be able to give examples of each.
• Classify and give examples of the seven different types of solutions (3 possible states for the solution and 3 combinations of phases of solute and solvent for the liquid and solid phase solutions).
Most everyday matter occurs as mixtures—combinations of two or more substances.
Objectives
Section 3.3 Mixtures of Matter
• Name and describe various mixture separation techniques and identify which technique would be most appropriate for a given separation problem.
• Describe the role that mobile and stationary phases play in chromatographic separation techniques.
• Describe how affinity differences play a role in liquid-liquid and chromatographic separation techniques. [material only partially in textbook]
Objectives (cont)
Section 3.3 Mixtures of Matter
Key Concepts
• A mixture is a physical blend of two or more pure substances in any proportion.
• Solutions are homogeneous mixtures.
• Mixtures can be separated by physical means. Common separation techniques include filtration, distillation, crystallization, sublimation, and chromatography.
Matter – Classification Scheme
Mixtures
Combination of two or more pure substances in which each pure substance retains its individual chemical properties
• Composition variable• Number of possible mixtures is infinite• Most everyday matter occurs as mixture
Mixtures - TypesHeterogeneous• Not smoothly blended [may appear to be
just by looking at it but will not be at the microscopic level]
• Individual substances remain distinct Sand & water Paint, mayonnaise [heterogeneous at a
microscopic level – not all heterogeneous mixtures are readily identified as such by the naked eye]
Mixtures - TypesHomogeneous• Constant composition throughout – even
down to the microscopic level• Single phase (gas, liquid or solid)
[although heterogeneous mixtures can also be a single phase such as a water/oil emulsion]
• More commonly used term is solution Salt & water
Mixtures and Compounds Iron and Sulfur
S
Fe
Physically mixed - can be separated by physical means
React chemically - cannot be separated by physical means
Solutions - TypesTable 3.3 “Types of Solution Systems” from the textbook; table 3.3 is not completely correct
Liquid-gas example wrong – water droplets are 2nd phase (incompatible with definition of solution)
Liquid-liquid example misleading – seawater itself is a solution of a solid dissolved in liquid water, so liquid is same for both; much better example is solution formed from 2 pure liquids, such as a solution of isopropyl alcohol in water (what you get from a drugstore)
Solutions - TypesOn the next slide is an expanded (and correct) version of Table 3.3
1st column is phase of solution itself
2nd column is phase of solute – the “stuff” that is being dissolved in the solvent to form the solution
By definition there is less of the solute than there is of the solvent
3rd column is phase of solvent
Can dissolve both gas & liquid in a solid!
Types of SolutionsPhase
Solute(Minor)
Solvent(Major)
Example
G Gas Gas Air – N2, O2, Ar
L Gas Liquid Soda – CO2 /H2O
L Liquid Liquid Antifreeze – Glycol / H2O
L Solid Liquid Salt water
S Gas Solid H2 in Pd or Pt
S Liquid Solid Dental Amalgam (Hg/Ag)
S Solid Solid Brass (Cu/Zn alloy)
SolutionsThe following 3 slides are intended as examples of how common substances such as air and water can be more complicated than one might expect
You are not expected to know the actual compositions
Composition of Dry Air (Solution)
Layers of AtmosphereSolution with continuously variable composition
Horizontally homogeneous (sort of – lots of point sources of pollutants)Vertically inhomogeneous but still a solution in local region
Substances Found in Natural Waters
Any natural water (tap or bottled) is a complicated homogeneous mixture (a solution) and if dust and sand/soil particles are counted, is a heterogeneous mixture
Separating MixturesTake advantage of differing physical propertiesFiltration – heterogeneous mixture• Solid from liquid
Distillation – typically liquid-liquid solutions; also solid-liquid (salt water)
• Depends upon difference in boiling points• Most volatile (lower bp) material removed 1st
Crystallization – liquid-solid solutions• Remove enough solvent so solubility of solute
exceeded – very high purity crystals possible
Separating MixturesSublimation (Phase change process in which solid changes directly into vapor) – can use in separation of solids if only one sublimates [extremely limited in actual practice]
Chromatography – separates components of mixture (mobile phase) based on ability of each component to travel across surface of another material (stationary phase) [this is most widely used separation technique in chemistry]
Filtration Good for Solid/Liquid Separations
Selective CrystallizationWhen KNO3(s) crystallized from aqueous solution of KNO3 containing CuSO4
(blue) as an impurity, CuSO4 remains in solution
KNO3 (white) crystallized from hot, saturated solution is virtually pure
Zone Refining of SiliconPurification by Crystallization
Heated (melted) zone moving left to right
Simple DistillationSeparation technique based on differences in boiling points (BPs) of substances involved – physical process, not chemical
Distillation often synonymous with “simple” distillation; single evaporation followed by condensation of vapors
Simple distillation - works well when BPs differ by ≥ 25 C (rule of thumb)
Batch technique (single filling of apparatus)
Gas
Gasoline 38 oC
Kerosene 150 oCHeating oil 260 oC
Lubricating oil 315 oC - 370 oC
Crude oil from heater
SteamResidue (asphalt, tar)
CondenserGasoline vapors
Fractional Distillation of Crude
Oil
Separating Mixtures
Forces exist between molecules
Details of molecular shape, size, and charge influence magnitude of force between any 2 molecules
For example, there are strong forces between oppositely charged molecules (ions)
Separating Mixtures
Forces between certain types of molecules are stronger than than for other types of molecules
• Ones with stronger forces said to have an affinity for each other
Can use affinity differences as basis for a separation technique
Separating Mixtures - PartitioningSolution with A & B dissolved in water
If A has higher affinity for another solvent than B does, can exploit to separate A & B
If water & 2nd solvent in contact, A will tend to concentrate in 2nd solvent
A & B said to partition between the 2 solvents – basis for liquid-liquid extraction process
Liquid-Liquid Extraction
2 substances dissolved in
water
Separatory Funnel
S
S2
S1
Wait for partitioning, then drain off bottom
S
Add 2nd immiscible (insoluble)
solvent & shake
Chromatography
Can exploit affinity differences in different way by using chromatography
Key to technique is mobile (moving) phase and a stationary phase
Molecules separate out on basis of their affinity for stationary phase
Stationary Phase
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
ChromatographyImportant and widely used technique
Many types: (m)=mobile (s)=stationary• VPC vapor phase – gas (m)/liquid (s)• LPC liquid phase – liquid(m)/solid(s)• Paper – liquid(m)/paper(s)• HPLC – high pressure LPC• IEC – ion exchange – ions (m)/resin(s)
Lots of others, often coupled with other types of instruments
Paper chromatography of ink(a) Line of mixture to be separated placed at one end of sheet of porous paper
Paper chromatography of ink(b) The paper acts as wick to draw upliquid
Paper chromatography of ink(c) Component with weakest attraction (least affinity) for paper travels faster than components that cling to paper (have high affinity for paper)
Column Chromatography
Gas Chromatography
Chromatographic Data
Data (chromatogram) is usually represented as a plot of “some” detector response as a function of either time or volume (chromatos = color)
Dete
cto
rR
esp
on
se
time or volume
3.1 Properties of Matter
3.2 Changes in Matter
3.3 Mixtures of Matter
3.4 Elements and Compounds (for treatment of simple hydrocarbons and isomers, see ppt Section 21.4 & Related – Isomers)Note: Laws of Definite Proportion & Multiple Proportion are included just for completeness but will be actually discussed when studying chapter 10 (The Mole)
Chapt 3 Matter – Properties & Change
Section 3.4 Elements and Compounds
• Define and distinguish between elements and compounds and recognize that a compound’s properties can be very different from the properties of its constituent elements.
• Identify a method for separating a compound into elements.• Classify a given material as a mixture or a pure substance
and to further classify it as homogeneous or heterogeneous mixture or as an element or as a compound. Should also be able to give an example of each category
• Describe the organization of elements in the periodic table.• Identify the number of currently recognized elements and
the number of naturally occuring elements
A compound is a combination of two or more elements.
Objectives
Section 3.4 Elements and Compounds
• Name the two most abundant elements in the universe and the five most abundant elements in the Earth’s crust, atmosphere and oceans (both sets in order of relative abundance). [Material not entirely in book]
• Distinguish between common & systematic chemical names.
• Name and describe the commonly used chemical identifiers
• Explain the value of a CAS registry number (or other comparable chemical identifiers) in finding information on existing compounds. [Material not in book]
• Identify the SMILES and InChI strings as chemical identifiers that are based on chemical structure and describe the advantages of these identifiers. [Material not in book]
Objectives (cont)
Section 3.4 Elements and CompoundsKey Concepts
• Elements cannot be broken down into simpler substances.
• Elements are organized in the periodic table of the elements.
• Compounds are chemical combinations of two or more elements and their properties differ from the properties of their component elements.
• Chemical registry numbers and other chemical identifiers help avoid some problems with complicated chemical names and make it easier to find information about compounds. In some cases, they provide a way to look for information based on the compound’s structure.
Matter – Classification Scheme
ElementsPure substance that can’t be separated into simpler substances by physical or chemical means
92 naturally occurring elements (Tc, # 43, only in trace amounts - unstable) – remaining elements must be synthesized
ElementsElements have name and chemical symbol
Named elements have 1 or 2 letter symbol with only 1st letter capitalized (C, Au, Pt)
Unnamed or undiscovered elements given 3 letter placeholder (temporary) symbol (Uut, Uuo) and latin or latin/greek name for its atomic number
Uuo = Ununoctium = latin for 118 + “ium”
Elements – Periodic TableOrganized into periodic table of elements (see end of book or pages 178-9) ordered by atomic number (number of protons in nucleus); currently 114 named elements
Columns (vertical) = groups or families
Elements in same group tend to have similar chemical and physical properties
Rows (horizontal) = periods
Table “periodic” because pattern of variation of properties repeats in each period
Elements - NewestElements with atomic numbers 114 and 116 officially named 5/2012 as Flerovium (Fl) and Livermorium (Lv), respectively. Copernicium (Cn), atomic number 112 officially named 2/2010.
Elements 113, 115, 117 (newest – April 2010), 118 have claimed to have been made, but evidence not yet convincing enough for official recognition by IUPAC
Official current total = 114 elements
Periodic Table of ElementsEach box shows atomic number and the element’s symbol
Newest elements Fl & Lv; remainder claimed to have been made but have not been officially recognized as existing
Periodic Table – Basic HistoryOriginal form of table published by Russian chemist Dmitri Mendeleev in 1869
Based on similar properties and ordered by element masses
Has since been refined – see chapter 6 (The Periodic Table and Periodic Law)
Elements - Abundance
Hydrogen most abundant and helium second most abundant elements in universe (H estimated to make up ~ 75% of mass of universe)
Statistics for elemental abundance on Earth focused on composition of Earth’s crust, its oceans and its atmosphere
Top five elements in order: O Si Al Fe Ca
Compound and Chemical FormulaFormed from 2 or more elements that are combined chemically (bonded to one another)
• Exception: S8 (1 element compound)
Simple compounds clearly and uniquely Identified by chemical formula - created from chemical symbols of elements and subscripts indicating number of atoms of that element
• H2O NaCl CH4 CaSO4
Overview – Identifying CompoundsWays of identifying a compound include:
1. Chemical formula
2. Chemical name
a. Common name
b. Systematic Name
3. Chemical structure (drawing)
4. Other (to be described)
Will use the term “chemical identifier” to refer to any of the above choices
Chemical Formula and Isomers
As compounds become more complex (especially organic ones), the chemical formula does not uniquely represent a single compound
Isomers – different compounds which have same chemical formula
Details are in PowerPoint presentation “Chapt 21 – Hydrocarbons [selected]” which covers simple alkanes and isomers of alkanes and other organic compounds
Systematic vs Common Names
Common names (water, aspirin) convey little to no chemical information
Elaborate rules exist for assigning names to chemical substances on basis of their structures – called systematic names
Systematic (rule-based) names uniquely identify given substance; rule definitions = system of chemical nomenclature
Chemical Nomenclature
Developed and kept up to date under auspices of International Union of Pure and Applied Chemistry (IUPAC), which publishes official (systematic) rules for naming organic and inorganic compounds
Primary aim - provide methodology for assigning descriptors (names and formulas) to chemical species so that they can be identified without ambiguity
http://en.wikipedia.org/wiki/IUPAC_nomenclature
Compound Names
Given substance may have several common or trivial names; ordinary cane sugar, for example, is more formally known as "sucrose“
Formal, systematic name for sucrose is α-D-glucopyranosyl-(1,2)-β-D-fructofuranoside
Compound Names - Drawbacks
Problems associated with names:
1. They aren’t necessarily unique; can be multiple ways of naming a given compound using the official rules of chemical nomenclature
2. For even moderately complicated compounds, can be difficult to figure out the correct name
3. Long, complex names are difficult to use in a search engine
Chemical Information & DatabasesTo find information about a substance from formal chemical database or from a less structured source of information (Google), need to be able to identify the substance using some sort of chemical identifier
Identifier could be common chemical name (table sugar, sucrose), a systematic chemical name [α-D-glucopyranosyl-(1,2)-β-D-fructofuranoside] or some alternate chemical identifier (like using SS number in place of person’s name to obtain data about a person)
Chemical Databases & Identifiers
Indexing of structure, composition and properties of new & existing compounds done by several organizations
To get around problem of complicated and multiple names for a substance, major databases of chemicals use chemical registry numbers, accession numbers or other chemical identifiers not based on name; some of these chemical identifiers are based directly on molecular structure
Chemical Databases & Identifiers
Chemical Abstracts Service (CAS) Registry Numbers are most commonly encountered chemical identifier for compounds (especially in US); also known as CAS RNs or CAS Numbers
Other registries and their associated chemical identifiers exist and offer alternatives / advantages to CAS numbers
Use of structure-based identifiers has accelerated over past 5 – 10 years
Compounds & CAS Registry Numbers
Number itself has no inherent chemical significance but provides an unambiguous, unique way to identify a chemical substance or molecular structure when there are many possible systematic, generic, proprietary, or trivial names
http://www.cas.org/index.htmlhttp://en.wikipedia.org/wiki/Chemical_abstracts
Compounds & CAS Registry Numbers
CAS number can contain up to 10 digits, divided by hyphens into 3 parts
Right most digit is a check digit used to verify the validity and uniqueness of number
Examples:• NaCl CAS [7647-14-5]• H2O CAS [7732-18-5]
Using CAS Number or Name
Many online databases will accept a CAS numbers as a search term
Wolframalpha (computational knowledge engine) accepts CAS numbers to provide extensive compound information – see example on left side of following slide
Right hand side of slide shows result from entering a compound name (benzoic acid); CAS number shown as part of output
http://www.wolframalpha.com/
Compounds from Wolfram Searchhttp://www.wolframalpha.com/input/?i=benzoic+acid
Other Registry Numbers and IDs
Wolframalpha and many other sources return a list of “chemical identifiers” – alternate ways that compound is indexed or described; benzoic acid identifiers:
Other IDs for Benzoic Acid - Wolframalpha
Other IDs for Benzoic Acid - Wikipedia
First hit from Google search on benzoic acid is Wikipedia article
Chemical IDs Listed by WikipediaMost important / widely used (not specific to a particular database)
CAS number – Chemical Abstracts Service Registry Number
InChI - textual identifier (text string) for chemical substances that represents chemical structures
SMILES – similar to InChI
CAS 134523-00-5 Atorvastatin (lowers cholesterol)
[R-(R*, R*)]-2-(4-fluorophenyl)-,-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenylamino)carbonyl]-1H-pyrrole-1-heptanoic acid OR
(3S,5S)-7-[2-(4-fluorophenyl)-3-phenyl-4-(phenylcarbamoyl)-5-propan-2-ylpyrrol-1-yl]-3,5-dihydroxyheptanoic acid
CAS Number & Chemical Name - Lipitor
Structure-Based Chemical Identifiers
Most direct is to draw compound’s structure (various ways of doing this)
Alternative is to encode connectivity (what’s connected to what) of atoms within a molecule into a text string
Two main string based IDs:
SMILES and InChI (IN chee)
SMILES
Simplified molecular input line entry specification - form of a line notation for describing structure of chemical molecules using short ASCII character stringsOC(=O)C(N)CC1=CC=C(O)C=C1 is an example of a SMILES string
SMILES strings can be imported by most molecule editors for conversion back into 2D drawings or 3D models of molecules
http://en.wikipedia.org/wiki/Simplified_molecular_input_line_entry_specification
IUPAC International Chemical Identifierhttp://en.wikipedia.org/wiki/International_Chemical_Identifier
InChI - textual identifier for chemical substances, designed to provide standard and human-readable way to encode molecular information & to facilitate database searches for such information
XML-based text coding system for chemical structure; codes are unique and capable of representing detailed and nuanced features of chemical structures for robust chemical structure representation
IUPAC International Chemical Identifierhttp://en.wikipedia.org/wiki/International_Chemical_Identifier
Examples of what are called “Standard InChI “ strings:
Chemical Identifiers for IsopreneMolecular formula: C5H8
Systematic names:
2-Methylbutadiene;
2-Methyl-1,3-butadiene
Common names:
Isoprene; Isopentadiene
CAS RN: 78-79-5
SMILES: C=CC(C)=C; C(C)=CC=C;
C(C=C)C=C; C=C(C=C)C
InChI: 1/C5H8/c1-4-5(2)3/h4H,1-2H2,3H3
Advantages of Structure-Based IDs
CAS RNs and similar registry numbers for other databases can only be used for existing compounds that have been registered by that database
Stucture-based IDs (InChI, SMILES) can encode compounds that might not exist
In addition, they allow for powerful structure-based searches such as “find existing compounds that have structures similar to my target compound”
Compound Identification - Summary
Chemical formula (NaCl, C3H8) OK for small compounds but not for larger organics – many, many compounds have same formula (isomers)
Common and formal chemical names (sodium chloride, propane) OK for small compounds but difficult for non-specialists to determine correct name for larger ones unless use computer and input structure
Compound Identification - SummaryRegistry numbers (CAS, etc.) good way to access information about existing compounds from chemical databases
InChI Chemical ID provides means to generate searchable ID from structure
SMILES Similar to InChI – encodes structure in text string
Structural formulas (easiest to digest)
Decomposing CompoundsCannot break down into components by physical means, but sometimes can by chemical means – requires input of energy because compound is more stable than its separate component elements
Electrolysis considered to be an example of a chemical process (doesn’t involve chemicals but does cause chemical change) that breaks down a compound – most common example is water electrolysis
Separating Water into Hydrogen and Oxygen Using Electrolysis
Separating Water into Hydrogen and Oxygen Using Electrolysis
Compounds
Properties can be quite different than component elements
See following slide on reaction of Na metal with chlorine gas to form NaCl
Some Properties of Sodium, Chlorine, and Sodium Chloride
Remainder of this section will be treated when doing chapter 10 (The
Mole)
Law of Definite Proportions
Regardless of amount, compound composed of same elements in same proportion by mass statement that compound’s formula doesn’t change with amount of compound present
• H2O = formula for water no matter how much water you have – proportions always same, mole ratio same, mass ratios same
Law of Definite (or Constant) Proportion
(or Composition)Both sources of
calcium carbonate (CaCO3) have same
% composition
Law of Definite Proportions
Focus here is % composition from some chemical analysis
% by mass = 100 mass element mass compound
Law of Definite Proportions% by mass = 100 mass element mass compound
Analysis of 20.00 g & 500.0 g samples same have same composition
Practice
Mass % & Law of Definite Proportions
Problems 19 - 23, page 88
Problem 29, page 90
Problems 72(a-b), 74 – 76 page 95
Problems 78, 80 page 96
Law of Multiple ProportionsIf elements form >1 compound, those compounds will have compositions that are small, whole-number multiples of each other
Focus: ratio of mass ratios = integer
Water vs Hydrogen Peroxide
H2O (O:H 16:2) vs H2O2 (O:H 32:2)• Ratio of Mass ratios
O:H (H2O2) / O:H (H2O) = 2:1
Atomic Basis of Law of Multiple Proportions
Ratio of number of atoms within each compound is integer ratio of mass ratios of compounds must be same integer
Law of Multiple Proportions
Compound I Compound II
Copper Chloride Compounds
Cpd % Cu % Cl Mass Ratio
Cu : Cl
Ratio: cpd I ratio to cpd II ratio
I 64.20 35.80 1.793 : 12.000
II 47.27 52.73 0.8964 : 1
Practice
Law of Multiple Proportions
Problems 27 - 28, page 90
Problems 77, 79 page 90
End of Chapter