Exam 1 Chem I31

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Exam 1 Chem I31
2012-07-04 17:01:09
UMD Summer 2012

measurements, #'s units, atoms, molecules, ions, compounds, chemical eqns, Stoichiometry, Percent Yield, Limiting Reactant
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  1. problem, question, answer, solution
    problem: a situation that presents difficulty, uncertainty, or perplexity

    question: a request for data; inquiry, interrogation, query

    answer: a spoken or written reply, as to a question

    solution: something worked out to explain, resolve, or provide a method for dealing with and settling a problem
  2. scientific method
  3. Units (5)
    • (1) time [seconds]
    • (2) length [meters]
    • (3) mass [grams]
    • (4) amount [moles]
    • (5) temperature [Kelvins]
  4. Qualitative vs. Quantitative
    qualitative observations: describe properties oroccurrences in ways that do not rely on numbers

    quantitative observations are measurements thatconsist of a number a unit and a label
  5. hypothesis
    a tentative explanation for the observations that may not be correct, but puts the scientist’s understanding of the system being studied into a form that can be tested
  6. experiments:
    • tests the validity of the hypothesis

    • are systematic observations or measurements made under controlled conditions, in which the variable of interest is clearly distinguished from any others

    • if experimental results are reproducible, they are summarized in a law
  7. law
    a verbal or mathematical description of a phenomenon that allows for general predictions that describes what happens and not why and is unlikely to change greatly over time unless a major experimental error is discovered
  8. theory
    attempts to explain why nature behaves as it does which is incomplete and imperfect and evolves with time to explain new facts as they are discovered
  9. Scientific Method
    a procedure that searches for answers to questions and solutions to problems, which consists of
  10. Law of Conservation of Mass
    • mass, or matter, can be neither created nor destroyed
    • *the total mass of substances does not change during a chemical reaction
  11. Law of the Conservation of Energy
    energy cannot be created or destroyed [1st Law of Thermodynamics]; this only applies to systems not involving nuclear reactions or velocities approaching the velocity of light
  12. Law of Definite Proportions
    when two or more elements combine to form a compound, their masses in that compound are in afixed and definite ratio (this data helps justify an atomic view of matter)
  13. Law of Multiple Proportions
    when two elements combine to form more than one compound, the mass of element A which combines in the first compound with a given amount of element B has a simple whole number ratio with the mass of element A which combines in the second compound with the same given mass of element B
  14. accuracy
    how closely measured values agree with the correct value
  15. precision
    how closely individual measurements agree with other measurements
  16. Significant Figures
    • • start at the left and proceed to the right
    • • if the number does not have a decimal point, count until there are no more non-zero numbers
    • • if the number has a decimal point, start counting at the first non-zero number and continue counting until you run out of decimal places

    • Multiplication/Division Rule
    • • product has the smallest number of significant figures of multipliers
    • - ex. 4.242 x 1.23 = 5.22 (3 sig figs)

    • Addition/Subtraction Rule
    • • answer contains smallest decimal place of the addends
    • - ex. 8.7937 - 2.123 = 6.671
  17. chemistry
    science that describes matter; its properties, composition, structure, the changes it undergoes, and the energy changes that accompany those processes
  18. matter
    anything that has mass and occupies space (*has volume)
  19. energy
    • the capacity to do work or transfer heat; chemical reactions always involve energy changes
    • - most processes lead to a lowering of the system's energy
  20. chemical properties
    observed only during chemical change/reaction; they describe the characteristic ability of a substance to react to form new substances

    - ex. rusting or oxidation, flammability and corrosion

    - a chemical change: is a change in the composition or identity of a substance (naturally accompanied by changes in physical & chemical properties
  21. physical properties
    can be measured/observed without changing the composition or identity of a substance

    - ex. mass, color, volume, amount of space occupied by the sample

    - physical change: a change in physical properties without any change in the composition or identity of a substance
  22. extensive properties
    • those properties that depend upon the amount of substance present

    -ex. mass, volume, energy, etc.
  23. intensive properties
    • other units apply to quantities which do not depend on 'sample size'
  24. -ex. density or temperature
  25. the states of matter
    • solids: have a fixed shape & volume; volume independent of temperature & pressure

    • liquids: have indefinite shape but fixed (definite) volume; assume the shape of their containers; volume independent of temperature & pressure

    • gasses: have indefinite shape & indefinite volume; expand to fill their containers; volume strongly dependent on temperature & pressure
  26. aqueous
    a substance which has been dissolved in water
  27. atomic number (Z)
    • number of protons in the nucleus of an atom of an element
    • -different for each element
  28. atomic symbol
    • abbreviation used to represent an atom in chemical formulas
  29. ion
    atoms or groups of atoms with a + or - charge formed by the addition or removal of electrons from an atom
  30. essential elements
    elements that are abolutely required in the diets of humans

    • • found only in the first two periods (rows) of the periodic table (2 exceptions: Mo & I)
    • • a deficiency in such an element causes abormality; can only be rectified using supplement of said element
  31. bulk elements (5)
    • C, H, O, N, S (chons...)
    • • building blocks of compounds that make up organs/muscles and consitute the bulk of our diet
    • • carbon, hydrogen, oxygen, nitrogen, sulfur
  32. macrominerals (6)
    elements that provide essential ions in body fluids & form major structural components of the body

    • • Na, Mg, K, Ca, Cl, P
    • (sodium, magnesium, potassium, calcium, chlorine, phosphorous)
  33. trace elements (7!)
    remaining essential elements; present in small amounts

    • • V, Cr, Ni, F, Sn, Si, As
    • (vanadium, chromium, nickel, flourine, tin, silicon, arsenic)
    • • many compounds of trace elements are toxic
  34. mass number
    • number of protons + neutrons in an atom
  35. density
    • • mass per unit volume; mass/volume = kg/m3
    • • liquids & solids: g/cm3
    • • gasses: g/L
  36. atomic mass
    the mass of a certain element (given in amu's); the one listed on the periodic table is the weighted average of the masses of said isotopes
  37. isotope
    • atoms that have the same number of protons but different numbers of neutrons
    • • all isotopes have the same chemical properties (b/c they have the same # of protons & electrons), they only differ in their atomic MASS

    • • ex. Carbon 12, 13, & 14
  38. exact numbers
  39. mass v. weight
    • • mass: a measure of the quantity of matter in an object
    • - the more mass something has, the more weight it will have
  40. • weight: the force that gravity exerts on an object
  41. heat v. temperature
    • heat: the transfer of thermal energy from a warm object TO a cooler object

    • temperature: a measure of the amount of thermal energy an object contains
  42. Conversion between Celcius and Kelvin
    • Tcelcius = Tkelvin - 273.15

    • Tkelvin = Tcelcius + 273.15
  43. volume
    • product of three lengths; for a rectangular solid = l * w * h m3

    • • metric volume units for fluid = Liters (L)
    • - 1 L = 1 dm3
    • - 1 mL = 1 cm3
  44. electrostatic attraction/repulsion
    • attraction: (+ & -) force between oppositely charged particles cause them to move TOWARD each other

    • repulsion: (+&+ or -&-) force between 2 particles that have the same charge causes them to repell each other

    -when attractive electrostatic forces are stronger than repulsive ones, atoms form chemical compounds and the interactions between atoms are called chemical bonds

    • • forces are dependent on
    • 1) mass (distance): the further away electrons/protons are from each other, the weaker the charge (regardless of charge, heavier atoms are larger than lighter ones)
    • 2) charge: the more charge, the stronger the forces (so charges of 4 and 1 are more attractive/repulsive than those of 1 and 1)
  45. ionic bonding
    one atom transfers electrons to another atom and the resultant oppositely charged particles 'stick together'

    • • involves a metal (cation) and either a 1) nonmetal (anion) or 2) polyatomic ion
    • • bond forms from the attraction between 2 oppositely charged particles

    • • the metal donates 1 or more electrons, forming a positively (+) charged ion = cation
    • • these electrons then enter the non-metal, causing it to form a negatively charged ion = anion

    • - electronegativity difference of 1.7 or more
    • -ex. NaCl or Al2O3
    • ionic compounds are not molecular
    • • there are NO discrete pairings (act in a group)

    • covalent compounds CAN have molecular formulas; they CAN be discrete (Covalent Can)
  47. ionic compounds
    • metals lose electrons to become cations (+ charged) & nonmetals gain electrons to become anions (- charged)

    • ionic compounds are held together by attractive electrostatic interactions between cations and anions

    • physical properties: form hard, crystalline solids that have high melting points (& are resistant to evaporation)
  48. binary ionic compounds
    • • ionic compound that contains only 2 elements, one present as a cation and one as an anion
    • • formula subscripts can be obtained using charges
  49. polyatomic ions
    • • groups of atoms that have a net electrical charge
    • • atoms IN polyatomic ion are held together by covalent bonds
    • • more polyatomic ions than monatomic ions
    • • more polyatomic ANions than cations
  50. covalent bonding
    • • bonds formed from atoms sharing electrons (therefore they stay near each other)
    • • occurs between 2 non-metals

    • - electronegativity difference of less than 1.7
    • -ex. O2, CH4
  51. compounds
    • a substance composed of two or more elements which are chemically united in fixed proportions by mass (due to law of definite proportions)
    • • can be separated by chemical but NOT physical means
    • -characters of each individual element are lost when they form a compound
  52. molecules
    the smallest unit of a compound that retains the characteristics of the compound
  53. chemical formula
    gives the composition of molecular compounds; is chemical symbols and the number of each representing composition

    1) empirical: simplest ratio of elements that does not represent the actual number and is non-positional

    2) molecular: gives only the number of each kind of atom present; chemical symbols and number of each element in a compoind; denotes actual composition but not position

    3) structural: shows which atoms are present & how they connect; chemical symbols and numbers of each element that represents both number and position
  54. types of structural formulas (4)
    1) condensed: ex. CH3OH

    2) ball & stick model

    3) space filling model

    4) wedge-dash model (or perspective drawing)
  55. waters of hydration
    • ionic compounds that contain specific ratios of loosely bound water molecules
    • • can be removed by heating