Chem review
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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

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Chem review

Chem Review


Experimentation

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

  • 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

Precision:

  • 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…

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:

Analysis:

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

    Conclusion:

  • 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


Safety

Safety

Goggles to protect against liquid splashes and vapors

Add acid to water

NEVER smell or taste without permission


Chemistry

Chemistry

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


Solutions

Solutions

  • 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


Solutions1

Solutions…

  • 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


Solutions2

Solutions…

  • 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)


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