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Chem Review. Experimentation. Scientific method: Problem – ask question Observations Hypothesis – educated guess; improves with experience and prior knowledge Experiment – tests hypothesis MUST be repeatable; reliability, error Steps called procedure; avoid bias

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Chem review

Chem Review


Scientific method:

  • Problem – ask question

  • Observations

  • Hypothesis – educated guess; improves with experience and prior knowledge

  • Experiment – tests hypothesis

  • MUST be repeatable; reliability, error

  • Steps called procedure; avoid bias

  • MUST consider all control variables (factors that could affect the outcome of experiment) when designing; makes results more valid

  • Affected by accuracy and precision

Precision and accuracy
Precision and Accuracy


  • How close measurements are to each other

  • Increases with better measuring equipment

  • Higher resolution (smaller intervals) is better

  • Example: graduated cylinder is better than a beaker, buret is better than a grad cyl

Precision and accuracy1
Precision and Accuracy…


  • How close the measurement is to the true value

  • Affected by calibration

  • 2 ways to look at improvement

  • Practice to improve with SAME instrument

  • Choose more precise instrument and automatically improves

  • Measurements should be both accurate and precise

Scientific method
Scientific Method

Last two steps:


  • Organize, evaluate, make inferences, and predict trends from data


  • Based on analysis of data and comparison to hypothesis

    Theory??? Still not a fact, theories may change over time

Opinion and fact
Opinion and Fact

Opinion: companies make advertisements are NOT fact; intended to persuade you

Fact: government studies and scientific research done by consumer magazines are usually more factual; no financial incentive to deceive you so more objective


Goggles to protect against liquid splashes and vapors

Add acid to water

NEVER smell or taste without permission


Periodic table: Locate

  • Metals – to the left of the stairstep

  • Nonmetals – to the right of the stairstep

  • Metalloids – along the stairstep

  • Group vertical column

  • Period – horizontal row

Chemistry periodic trends
Chemistry – Periodic Trends

Number of valence electrons increases with increasing group number

Number of energy levels increases with increasing period number

Noble gases – Group 18; don’t form compounds; very stable; already have filled outer energy levels (octet)

Chemistry classification of matter
Chemistry – Classification of Matter

Atom – smallest unit of a molecule or compound

Molecule – smallest unit of a substance

Element – made up of identical atoms; each element is identified by the # of protons

Compound –

  • Combination of two or more elements in an exact whole number ratio

  • Can only be separated chemically (break bonds)

Classification of matter
Classification of Matter…

Mixture –

  • Combination of 2 or more compounds; no specific ratio

  • Can separate using physical means like sorting or filtering

  • Heterogeneous – unevenly mixed; can usually see the different substances

  • Homogeneous – evenly mixed; called a solution (can be a combination of any of the states of matter)

Classification of matter1
Classification of Matter…

Physical change –

  • Same compound, just appears different; change of state, size, shape, mixture…

  • Done by physical means; force, average kinetic energy

  • Retains same chemical properties like boiling point, solubility, conductivity…

Classification of matter2
Classification of Matter…

Chemical change –

  • Different substance due to chemical reaction; rusting, fading, burning, cooking, digestion, respiration, photosynthesis

  • Done by chemical reactions involving energy transformations

  • Need activation energy to get started; from sun, ATP, another chemical reaction, heat source…

  • Gains new chemical property “signature”

  • Evidence – color change, odor, formation of a gas or precipitate

Classification of matter3
Classification of Matter…

Matter – particles; anything that has mass or takes up space

Mass – amount of matter an object has

Volume – amount of space an object takes up

Density – relates the object’s mass to its volume

  • Density effects many physical properties such as:

  • Viscosity – how easily a fluid flows

  • Buoyancy – how much upward force a fluid has or how much buoyant force is needed to make a solid float

Types of chemical bonds
Types of Chemical Bonds

  • Metallic – 2 or more of the same metal

  • Ionic – 1 metal and 1 nonmetal; metal atom gives away 1 or more electrons, nonmetal takes them; forms charged ions that are then attracted to each other to make a compound

  • Covalent – 2 or more different nonmetals; share electrons to make compound

  • Diatomic – exactly 2 of the same nonmetal

Types of chemical bonds1
Types of Chemical Bonds…

Polyatomic ion – 2 or more covalently bonded atoms that behave as a single unit to form ionic bonds with metals

Naming ionic compounds
Naming Ionic Compounds

  • Ignore subscripts and coefficents

  • Write full name of first element or polyatomic ion in compound include roman numerals if needed

  • Write the first syllable of second element plus –ide OR the full name of polyatomic ion

Naming covalent compounds
Naming Covalent Compounds

  • Use subscripts to determine prefix

  • Don’t use mono- if there is only one of the first element

  • Add –ide at the end

Writing formulas
Writing Formulas

  • Write chemical symbol for first element or polyatomic ion in name

  • Write chemical symbol of second element or polyatomic ion

  • Write the oxidation number of each element or ion above the symbol (charge) and crisscross to use as subscripts

  • If they aren’t the lowest whole number ratio reduce

Writing formulas1
Writing Formulas…

  • For covalent compounds just write the subscripts from the prefixes

Balancing equations
Balancing Equations

  • Purpose – to follow the law of conservation of mass

  • Reactants – compound on the left side of the equation

  • Products – compounds on the right side of the equation

  • Compare the number of each element on the left side of the equation to the right side

  • Use coefficents to make equal

  • If an element show up in 2 or more compounds on the same side of the equation, balance it last! Usually oxygen or hydrogen

  • Check for simplest ratio

Types of reactions
Types of Reactions

Based on chemical bonds

  • Synthesis: A + B  AB

  • Decomposition: AB A + B

  • Single displacement: A + CD  C + AD

  • Double displacement: AB + CD  CB + AD

  • Combustion: CxHy + O2  CO2 + H2O

Types of reactions1
Types of Reactions…

Based on energy

  • Exothermic: need less energy to make reaction happen than it gives off when reaction is complete – Example: explosions, hot packs, glow sticks, burning

  • Endothermic: need more energy to make reaction happen than it gives off when reaction is complete – Example: cold packs


  • Solvent – substance that does the dissolving (water)

  • Solute – substance that gets dissolved (sugar)

  • “Like dissolves Like”

  • Polar solvent can dissolve ionic and polar solutes (ions); water is the universal solvent

  • Nonpolar solvent can only dissolve nonpolar solutes


  • Solubility

  • How MUCH of a substance will dissolve in a certain amount of solvent and at a certain temperature

  • Increase temperature, increase solubility for most substances except gases


  • Factors affecting the rate of solubility solids

  • Increase surface area (crushing)

  • Increase temperature (usually)

  • Agitation (stir)

  • Factors affecting rate of solubility gases

  • Decrease temperature

  • Increase pressure

  • Dissolving is a physical change

Acids and bases
Acids and Bases

  • pH < 7 acid (lower the pH the stronger the acid)

  • pH = neutral

  • pH > 7 base (higher the pH the stronger the base)