Week 9 (Intro to Spectroscopy/Redox)

Question 1

Oxidation State

Answer 1

-degree of oxidation for an atom compared to its elemental state
-applies to ions as well as atoms involved in covalent bonds

Question 2

Positive Oxidation State

Answer 2

-indicates electrons have been lost or shared with more electronegative atoms

Question 3

Negative oxidation state

Answer 3

-indicates electrons have been gained or shared from less electronegative atoms

Question 4

Elemental form oxidation state

Answer 4

-oxidation state= 0
-occurs for diatomic atoms such as Cl₂

Question 5

Single atom ions oxidation state

Answer 5

-oxidation state= charge
-Cl⁻ = -1

Question 6

Atoms in covalent bonds oxidation state

Answer 6

-depends on other atoms present
-sum of oxidation states=overall charge

Question 7

Common oxidation states

Answer 7

-do not usually change due to dramatic electronegativity
-F = -1
-O = -2
-Group 1 = +1
-Group 2 = +2
-Group 17= -1

Question 8

Oxidation

Answer 8

-loss of electrons
-oxidation state increases

Question 9

Reduction

Answer 9

-gain of electrons
-oxidation state decreases

Question 10

Reducing agent

Answer 10

-electron donator, causes another atom to become reduced (gain electrons)
-loses electrons in process
-usually less electronegative (such as H, Group 1, and Group 2 metals)

Question 11

Oxidizing agent

Answer 11

-electron receiver, causes another atom to become oxidized (lose electrons)
-gains electrons in process
-usually more electronegative (such as O, halogens (F, Cl, Br), and H₂O₂)

Question 12

Oxidation number

Answer 12

-a book-keeping device used to keep track of the electrons “gained” or “lost” in an atom when it forms bonds with other atoms in molecules/polyatomic ions

Question 13

number of possible oxidation numbers in an atom

Answer 13

-possible oxidation numbers can be determined from the number of valence electrons
-ex.) Cl: 7 valence electrons, lowest possible O.N. is -1, highest possible O.N. is +7 (how many valence electrons it can lose/gain)
-ex.) C: 4 valence electrons, lowest possible O.N. is -4, highest possible O.N. is +4

Question 14

Guidelines for assigning O.N.

Answer 14

1. O.N. of free elements is always 0, while O.N. of monoatomic ions are the same as its charge (O.N. of Al is 0, O.N. of Al⁺³ is +3)
2. algebraic sum of O.N. of all atoms equals 0 for an electrically neutral molecule and equals the overall charge for an ionic species (NO₃⁻, 1(O.N. of N) + 3(O.N. of O) = -1)
3. Metals have a positive O.N. (group 1= +1, group 2= +2)
4. Nonmetals are assigned in such order (F= -1, H= +1, O= -2, group 17= -1, group 16= -2, group 15= -3)
5. Any remaining O.N. are filled by following rule 2
6. polyatomic ions can be used as a reference to break down larger molecules

Question 15

Carbon oxidation state

Answer 15

-determine if atoms are more or less electronegative than carbon
-give electrons in bond to more electronegative atom (if connected to another carbon, they share electrons and each get -1 charge)
-every line = 2 electrons

Question 16

Spectrophotometer

Answer 16

-instrument use to measure/study concentration of colored/light-absorbing chemicals in a solution
-shines light through sample and measures amount of light absorbed/transmitted
-1.00 cm path length is 2x length of 0.50 cm

Question 17

Steps for balancing redox reaction

Answer 17

1. use changes in oxidation number of elements in reactants/products to identify which species is being oxidized/reduced
2. write oxidation half-reaction and reduction half-reaction (balance elements whose oxidation numbers change, balance electrons gained/lost based on changes in oxidation number, balance net charges by adding H⁺ (when in acidic medium) or OH⁻ (when in basic medium) to either side, balance O and H by adding H₂O to either side)
3. Make the number of electrons gained from reduction half-reaction equal to number of electrons lost in oxidation half-reaction (by multiplying one or both half-reactions)
4. add the balanced oxidation and reduction half-reactions together such that the electrons gained cancel out the electrons lost

Question 18

Wavelength and Color

Answer 18

-the color of a species’s wavelength is the complementary (transmitted) color
-(ex. if a species absorbs yellow-green, it will appear violet)