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Chem Review

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

emma-wood
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Chem Review

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  1. Chem Review

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Safety Goggles to protect against liquid splashes and vapors Add acid to water NEVER smell or taste without permission

  8. 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

  9. 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)

  10. 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)

  11. 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)

  12. 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…

  13. 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

  14. 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

  15. 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

  16. Types of Chemical Bonds… Polyatomic ion – 2 or more covalently bonded atoms that behave as a single unit to form ionic bonds with metals

  17. 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

  18. 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

  19. 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

  20. Writing Formulas… • For covalent compounds just write the subscripts from the prefixes

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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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