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chem 1/2 2022 > electrochemistry I > Flashcards

electrochemistry I Flashcards

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1
Q

what is a redox reaction?

A

donation (transfer) of electrons from one substance to another

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2
Q

key features of a redox reaction?

A

-involves electron transfer
-one substance must donate electrons and one substance must accept electrons
-the substance that donates electrons (loses) = oxidised
-the substance that accepts electrons (gains) = reduced

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3
Q

oxidation can be identified by:

A

-loss of electrons (on RHS of half equation)
-increase in oxidation number
-gaining of oxygen
-loss of hydrogen

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4
Q

reduction can be identified by:

A

-gain of electrons (found on LHS of half equation)
-decrease in oxidation number
-loss of oxygen
-gain of hydrogen

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5
Q

what must you ensure in a half equation?

A

that the charges are BALANCED

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6
Q

writing an overall redox equation?

A

-the number of electrons lost during oxidation MUST EQUAL the number of electrons gained during reduction
-treat like maths simultaneous equations, cancel out e-

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7
Q

define electronegativity:

A

a measure of the tendency of an atom (of that element) to attract a bonding pair of electrons

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8
Q

what are oxidants?

A

reactants that cause another substance to be OXIDISED. it pulls electrons away from something else, causing that substance to LOSE ELECTRONS

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9
Q

what are reductants?

A

reactants that cause another substance to be reduced

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10
Q

what side of the half equation is reduction?

A

LHS - gaining electrons (RHS NOT RED)

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11
Q

what side of the half equation is oxidation?

A

RHS - losing electrons

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12
Q

general oxidants and reductants

A

halogens (group 17) = oxidants
halogen ions = reductants
metals = reductants
metal ions = oxidants

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13
Q

define oxidation number

A

a measure of the electron density around an atom, compared to its elemental form

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14
Q

is 4+ or +4 an oxidation number (O.N)

A

+4
sign comes before number

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15
Q

trend of electronegativity and O.N

A

more electronegative elements = negative oxidation numbers
less electronegative elements = positive oxidation numbers

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16
Q

rule 1 for O.N

A
  1. the sum of all the oxidation numbers in any substance is equal to the total charge. this means that the elemental form will always have an oxidation number of ZERO
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17
Q

rules 2 and 3 of O.N

A
  1. fluorine has an oxidation number of -1 in compounds
  2. group 1 metals are +1 in compounds, group 2 metals are +2 in compounds
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18
Q

rules 4 and 5 for O.N

A
  1. when H is bonded to non-metals, it has O.N of +1, when H is bonded to metals, it has O.N of -1
  2. oxygen has oxidation number of -2 in compounds, but in peroxides, it has O.N of -1
19
Q

rules 6 and 7 of O.N

A
  1. grp 7 elements are usually -1 in compounds. if two ore more different grp 7 elements are present, the more electronegative one if -1
  2. in absence of other info, grp 16 non-metals = usually -2, grp 15 non-metals = usually -3 and grp 3 metals are usually +3
20
Q

outline the steps of KOHES

A
  1. identify Key element in half equation + balance
  2. balance number of Oxygen atoms (by adding water to other side)
  3. balance number of Hydrogen atoms (by adding H+ ions)
  4. balance charges on both sides by adding electrons to more pos side
  5. add state symbols
21
Q

what are redox conjugate pairs?

A

a conjugate redox pair (one=reactant and one=product) share an atom that have gained or lost electrons

22
Q

what pairs exist in redox conj. pairs?

A

reductant at start - conjugate oxidant formed at end
oxidant at start - conjugate reductant formed at end

23
Q

what is the direction of electron transfer in a redox reaction?

A

FROM oxidised substance TO reduced substance

24
Q

what is a galvanic cell?

A

a chemical system that produced an electric current (DC) from a spontaneous redox reaction

25
Q

key features of a galvanic cell:

A

-contains two half cells, each containing a conjugate redox pair
-on electrode in each half cell - these conduct electricity
-contains a salt bridge
-contains anode and cathode

26
Q

define anode

A

the site of oxidation
it is a NEGATIVE terminal (aNode = Neg)

27
Q

define cathode

A

the site of reduction
it is a POSITIVE terminal (ca+hode = +)

28
Q

what is the purpose of a salt bridge?

A

contains unreactive ions that maintain an even distribution of ions in each beaker + counteract any imbalance of charge and complete the electrical circuit
common = KNO3

29
Q

movement of ions from salt bridge into half-cells?

A

anions (neg) go to anode (neg)
cations (pos) go to cathode (pos)

30
Q

what does each half-cell contain?

A

each contains an electrode in contact with a solution. the species present in each half cell form a conjugate redox pair eg. Zn and Zn2+

31
Q

direct contact in galvanic cells

A

when oxidant and reductant = in direct contact, electron transfer cannot be detected t/f energy is released in form of HEAT

32
Q

galvanic cell electrical flow?

A

electrons are forced to travel along the external wiring to reach the substance that is being reduced (oxidant) t/f this is detected by a voltmeter or an ammeter = ELECTRICAL ENERGY

33
Q

what is the mnemonic to remember??

A

AN OIL RIG CAT

34
Q

what is the direction of electron transfer in a galvanic cell?

A

from anode to cathode

35
Q

why must both oxidation and reduction occur simultaneously during any redox reaction?

A

because the loss of electrons by one substance must be accompanied by a gain of electrons in another substance

36
Q

define displacement reaction

A

a type of redox reaction between a more reactive element and a compound containing a less reactive element, resulting in the less reactive element being displaced from the compound

37
Q

what is a conjugate oxidant?

A

a substance produced when a reductant loses electrons, containing the element that has increased in oxidation number

38
Q

what is a conjugate reductant?

A

a substance produced when an oxidant gains electrons, containing the element that has decreased in oxidation number

39
Q

standard electrode potential E^o

A

the relative strength of the oxidant under standard conditions, compared to the H+/H2 half cells (0V). measured as a voltage produced

40
Q

standard cell potential (E^0 cell)

A

the voltage/potential difference across two half-cells under standard conditions -> calculation = E cathode - E anode

41
Q

electrochemical species and spontaneous reactions

A

an electrochemical species compares the relative strength of oxidants and reductants, so it can be used to predict whether a reaction will occur spontaneously (a redox reaction will occur)

will only occur if oxidant (left) = HIGHER than reductant (right side of half equation) NEED NEGATIVE GRADIENT

42
Q

metal reactivity series acronym

A

police sergeant lieutenant commander MACZINTL has caught me stealing gold plates

43
Q

what is the metal reactivity series?

A

potassium, sodium, lithium, calcium, magnesium, aluminium, CARBON, zinc, iron, nickel, tin, lead, HYDROGEN, copper, mercury, silver, gold, platinum

44
Q

why can a metal displace another metal in a compound?

A

because it is a more reactive element that can displace a less reactive metal element from its compound and because it is a stronger reductant

chem 1/2 2022 (11 decks)

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