ch. 1 introduction: some basic concepts
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Ch. 1 Introduction: Some Basic Concepts. The study of the composition of matter and the changes that matter undergoes. Chemistry. Matter. Anything that has mass and takes up space. States of Matter. Solid. Definite shape AND volume Incompressible Particles are packed tightly together. - PowerPoint PPT PresentationTRANSCRIPT
Ch. 1 Introduction: Some Basic Concepts
Chemistry
• The study of the composition of matter and the changes that matter undergoes
Matter
• Anything that has mass and takes up space
States of Matter
Solid
• Definite shape AND volume• Incompressible• Particles are packed tightly together
Liquid
• Definite volume• Takes the shape of its container• Almost incompressible-particles not rigidly
packed
Gas• Takes the volume and the shape of its
container• Particles in a gas are spaced far apart• Easily compressed
Vapor
• The gaseous state of a substance that is generally a solid or a liquid at room temperature
Physical Properties• A quality or condition that can be observed or
measured without changing the substances composition
• Color, solubility, odor, hardness, density, melting point, boiling point
Physical Change
• Changes the material without changing the composition
• Boiling, freezing, dissolving, melting, condensing, breaking, splitting, cracking, cutting, crushing, bending………
• Usually reversible
Pure Substance
• Contain only one kind of matter• Have identical physical properties
Elements
• The simplest forms of matter that can exist under laboratory condition
• Can not be separated into simpler substances by chemical means
• The building blocks for all other substances
Chemical Symbol
• One or 2 letters• The first letter is always capitalized
Compounds
• 2 or more elements chemically combined• Can be separated into simpler substances by
chemical means
Sodium Metal
+Chlorine Gas
=Sodium Chloride
Compounds• The subscript numbers in chemical formulas
represent the proportions of elements that make up the compounds
• Pb2(SO4)3
• Pb (lead) 2• S(Sulfur) 3• Oxygen 12
Law of Definite Proportions (Law of Constant Composition)
• The elemental composition of a pure compound is ALWAYS the same
• i.e. Water= H2O = 2 Hydrogens: 1 Oxygen ALWAYS
2 Types of Mixtures
• Heterogeneous Mixtures• Homogeneous Mixtures
Mixture
• A physical blend of 2 substances• Compositions may vary
Heterogeneous Mixture
• One that is NOT uniform in composition
Homogeneous Mixture
• The same throughout
Solution
• A homogeneous mixture• Solutions may be solids, liquids, or gases• Same composition throughout
Phase
• Any part of a system with uniform composition and properties
Phase 1
Phase 2
Separation of Mixtures
Distillation
Separation of Mixtures
Centrifuge
Separation of Mixtures
Chemical Property• The ability of a substance to undergo a
chemical reaction to form a new substance
• I.e. flammability, alkalinity, acidity, rusting
• Chemical properties are only observed when a substance undergoes a chemical change
Chemical Changes (Reaction)
• One or more substances change into new substances
• 2 H2 (g) + O2 (g) 2 H2O (g)
Reactants Products
Chemical Reactions (rust-oxidation)
Chemical Reactions (combustion)
Chemical Reactions (acid/base)
Indicators of a Chemical Reaction
1. Energy is absorbed or given off (change in temperature)
2. Change in color3. Change in odor4. Formation of a solid (precipitation)5. Formation of a gas
Scientific Method
• One logical, systematic approach to the solution of scientific problems. Steps include:
1. Making observations2. Testing hypothesis3. Developing theories
Observation
• Use your senses to obtain information directly
Hypothesis
• A proposed explanation for an observation based on previous knowledge (or research)
• Must be specific• Must be testable• Is only useful if it accounts for what is actually
observed
Experiment
• A means to test a hypothesis
Manipulated Variable (Independent Variable)
• The variable that you can change• Time• Temperature• Volume• Speed• Pressure
Independent Variable
Responding Variable (Dependent Variable)
• The variable that is observed during the experiment
Dependent Variable
• For the results of an experiment to be accepted the experiment must produce the same results no matter how many times it is repeated or by whom
Theory
• A broad and extensively tested explanation of why experiments give certain results.
• A theory can NEVER be proven because a new experiment can always disprove it
Scientific Law
• A concise statement that summarizes the results of many observations and experiments.
• Scientific law describes natural phenomena without attempting to explain it
Qualitative Observation
• Give results in a descriptive non-numerical form
• Subjective• Ex. The solution is green, The precipitate is
fluffy
Quantitative Observation
• Gives results in a definite form• Numbers and units
Measurement
• A quantity that has both a number and a unit
• Measurements are only as exact as the instrument used to take it
International System of Units (SI)
• Length = meter(m)• Mass = gram (g)• Temperature = kelvin (K) although often we
will use Celsius• Time = second (s)• Amount of substance = mole (mol)• Volume = liter (L)
Prefixes
• Mega (M) = 106
• Kilo (k) = 103
• Deci (d) = 10-1
• Centi (c) = 10-2
• Milli (m) = 10-3
• Micro () 10-6
• Nano (n) = 10-9
• Pico (p) = 10-12
Length
• The distance between 2 points• Unit: meter (m)
Mass
• The amount of matter an object has• Units: Grams• Measuring tools: Triple Beam Balance,
Electronic scale, Analytical Scale
Temperature
• Measure of how hot or cold an object is• Determines heat transfer (moves from high to
low)• Almost all substances expand when heated-
contract when cooled (except water)• Units: Kelvin (K) = Celsius (c) + 273
Volume
• The amount of space an object (substance) occupies
• Units: Liter (L)
Density
• The amount of matter in a given volume
• Density = mass volume• D= m/v
Density
• Depends only on the composition of a substance NOT on the size of the sample
• With a mixture the density can vary because the composition of the mixture can vary
Density
• The density of a substance generally decreases as its temperature increases therefore temperature of the substance must always be noted
Accuracy
• how close a measurement comes to the actual or true value of whatever is measured must be compared to the correct value
Precision
• How close a series of measurements are to one another depends on more than one measurement
Significant Figures
• In a measurement, includes ALL of the digits that are known plus the last digit that is estimated
• Measurements MUST ALWAYS be reported to the correct number of sigfigs because calculated answers depend on sigfigs
Rules for Significant Figures
1. Nonzero numbers are ALWAYS significant-13.24 cm = 4 sigfigs- 3.5 mL = 2 sigfigs-123.456 g = 6 sigfigs
Rules for Significant Figures
2. Captive zeros are ALWAYS significant- 1023 g = 4 sigfigs- 1.0005 cm = 5 sigfigs
Rules for Significant Figures
3. Leading Zeros (zeros in front of nonzero numbers) NEVER count- 0.53 cm = 2 sigfigs- 0.0000000000053 cm = 2 sigfigs
Rules for Significant Figures
4. Zeros at the end of a number only count if there is a decimal point- 100 mL = 1 sigfig-100.0 mL = 4 sigfigs-100.00 mL = 5 sigfigs
Rules for Significant Figures
5. Scientific Notation: Only consider the coefficients when determining sigfigs- 1.2 x 104 mL = 2 sigfigs- 1.06 x 10-6 m = 3 sigfigs
Rules for Significant Figures
6. Exact numbers (counting) or exactly defined quantities have unlimited number of sigfigs- 35 students = unlimited sigfigs- 1 min = 60 seconds = unlimited sigfigs
Significant Figures in Calculations
• A calculated value can NEVER be more precise than a measured value
Significant Figures in Calculations
• Addition and subtraction:• The answer should be rounded to the same number of
decimal places as the measurement with the least number of decimal places
• 135.75 mL (2 decimal places)+ 57.6 mL (1 decimal place) 193.35 mL = 193.4 mL (answer has 1 decimal place)
Rounding
• X > 5 Round up
• X < 5 Round down
• Only look at the number next to the one you are rounding
Significant Figures in Calculations
• Multiplication and Division• Round the answer to the same number of significant
figures as the number with the least number of sigfigs.
• 35.062 g ( 5 sigfigs) = 1.492 g/mL (4 sigfigs) 23.50 mL (4 sigfigs)
Dimensional Analysis
1. Always start with the number given in the problem)
2. Units that you want to cancel go on the bottom
3. When a number is on top, multiply4. When the number is on the bottom, divide
Example
• Convert 153 lb to grams (hint: 1 lb = 453.6 g)
Example
• 153 lb X 453.6 g = 69400.8g=69400g (3sigfigs) 1 lb