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chemistry > reactivity 3.2 > Flashcards

reactivity 3.2 Flashcards

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1
Q

note packets! (3.2.1 and 3.2.2)

A
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2
Q

how do metals (groups 1 & 2) change down a group (in relative ease of oxidation)?

A

the relative ease of oxidation increases

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3
Q

halogens are ______ agents. why?

A

oxidising agents, because they react with metals by accepting an e- from the metal atom

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4
Q

how does oxidising power of halogens change down a group? why?

A

decreases, halogens get less reactive

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5
Q

when does halogen displacement occur?

A

when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide

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6
Q

what is the reactivity series (aka activity series)?

A

the ranking of metals in order of reactivity

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7
Q

what is a metal displacement reaction?

A

when metals higher in reactivity displace less reactive metals from their compounds in solutions or from their oxides

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8
Q

in a metal displacement reaction, which metal is the reducing agent? how does this determine ranking?

A

the more reactive metal, as this allows metals to be ranked from most reactive (strongest reducing agents) to least reactive

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9
Q

how can the reactions of acids and metals can be written as ionic equations?

A

showing only the species that has changed in the reaction

eg.
2HCl (aq) + Zn (s) → ZnCl2 (aq) + H2 (g)
turns into
2H+ (aq) + 2Cl– (aq) + Zn (s) → Zn2+ (aq) + 2Cl– (aq) + H2 (g)
turns into
2H+ (aq) + Zn (s) → Zn2+ (aq) + H2 (g)

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10
Q

define voltaic cells

A

a cell that generates a potential difference known as an electromotive force (EMF)

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11
Q

EMF is also known as ____. symbol representing this is __

A

cell potential, italicized E

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12
Q

voltaic cells are also known as _______ cells

A

galvanic

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13
Q

how can the absolute value of a cell’s potential be determined?

A

with the difference between one cell and another

think of it like arm-wrestling: you cannot determine the strength of an arm-wrestler unless you compare them to the other competitors

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14
Q

how do voltaic cells generate electricity?

A

from spontaneous redox reactions

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15
Q

Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)

instead of electrons being transferred directly from the zinc to the copper ions, a cell is built which separates the two redox processes. what is each part called?

A

a half-cell

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16
Q

what is the purpose of dipping a rod of metal into a solution of its own ions?

A

to set up an equilbrium

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17
Q

look at sme notes primary cells for zinc example!! very important

A

-

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18
Q

how is an EMF established?

A

if two different electrodes are connected, the potential difference between the two electrodes will cause a current to flow between them

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19
Q

how is a typical electrochemical cell made?

A

by combining a zinc electrode in a solution of zinc sulfate with a copper electrode in a solution of copper sulfate

(called a zinc-copper voltaic cell (AKA daniell cell)
(look at sme for this visual)

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20
Q

what allows ions to flow from one solution to another in a volatic cell? (what is it called & made of?)

A

a salt bridge, usually a piece of filter paper saturated with a solution of an inert electrolyte

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21
Q

what can EMF be measured with?

A

voltmeter

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22
Q

the two half cells are said to be __ _____ as the same current is flowing through both cells

A

in series

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23
Q

shorthand convention for electrochemical cell representation:

solid vertical (or slanted) line

A

shows a phase boundary (an interface between a solid and solution

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24
Q

shorthand convention for electrochemical cell representation:

double vertical line (sometimes seen as dashed vertical lines)

A

salt bridge

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25
Q

what are examples of chemical solutions used to make a salt bridge? x2, why? x1

A

potassium chloride
potassium nitrate

used because chlorides and nitrates are usually soluble

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26
Q

why is it necessary for the solution used to form a salt bridge to be soluble?

A

ensures that no precipitates form, as they could affect the equilibrium position of the half cells

27
Q

which substance in each half cell is drawn next to the salt bridge?

A

highest oxidation state

28
Q

how is cell potential difference shown?

A

with the polarity of the right-hand electrode

29
Q

what can be deduced from this?

Zn (s)∣Zn^2+ (aq) ∥Cu^2+ (aq)∣Cu (s)

E cell = +1.10 V

A

that the copper half-cell is more positive than the zinc half-cell so that electrons would flow from the zinc to the copper

30
Q

review fuel cells, esp h-o

A

-

31
Q

benefits of hydrogen-oxygen fuel cells x3

A

water is the only product (obvi more environmentally safe than other fuel cells, such as how other produce harmful nitrous oxides)

all the bond energy is converted into electrical energy instead of heat and light because it is takes place at room temp

have use on spacecrafts, supplies drinking water

32
Q

risks & problems of hydrogen-oxygen fuel cells x4

A

hydrogen gas is highly flammable

expensive to store H gas safely & generally expensive

production of H is a by-product of crude oil industry (reliant on finite resource)

H has high energy density, but is a gas so E density per unit volume is low (needs large containers compared to liquid fuels)

33
Q

how do electrolytic cells drive chemical reactions using electrical energy?

A

an electric current reverses the normal directions of chemical change and this is non-spontaneous

34
Q

in electrochemical cells, where do oxidation and reduction take place?

A

oxidation takes place at the anode and reduction will occur at the cathode

35
Q

in voltaic cells the anode is +/-?
in electrolytic cells the anode is +/-?

A

in voltaic cells the anode is negative
in electrolytic cells the anode is positive

36
Q

how do secondary/rechargeable cells work?

A

they employ chemical reactions which can be reversed by applying a voltage greater than the cell voltage, causing electrons to push in the opposite direction

37
Q

3 common examples of secondary cells

A

lead-acid batteries
nickel-cadmium / NiCad cells
lithium cells

38
Q

composition of lead-acid batteries

A

consist of six cells joined together in series

39
Q

how do lead-acid batteries work?

A

cells use lead metal as the negative electrode and lead(IV) oxide as the positive electrode

40
Q

what electrolyte is used in lead-acid batteries?

A

sulfuric acid

41
Q

lead acid batteries generate an EMF of about __ V, making the combined 6 cells give a combined voltage of about __ V

A

2, 12

42
Q

what are lead-acid batteries used for? where are they often utilised?

A

designed to produce a high current for a short period of time

powering a starter motor in car engines

43
Q

disadvantages of lead-acid batteries x3

A

very heavy

contain toxic materials: lead and lead(IV) oxide

sulfuric acid electrolyte is very corrosive

44
Q

in NiCad cells, the ______ electrode consists of cadmium and the ______ electrode is made of a nickel(II) hydroxide-oxide system

A

negative, positive

45
Q

disadvantages of NiCad cells x2

A

expensive

cadmium is a toxic metal

46
Q

what are lithium-ion cells used for?

A

powering electronic devices

47
Q

why is lithium used in lithium-ion cells?

A

it has a very low density and relatively high electrode potential

48
Q

what makes up a lithium-ion cell? x3

A

a positive lithium cobalt oxide electrode

a negative carbon electrode

a porous polymer membrane electrolyte

49
Q

what is the advantage to using a porous polymer membrane in lithium-ion cells?

A

the polymer electrolyte cannot leak since it is not a liquid or paste

50
Q

EMF generated by lithium-ion cells, X to X

A

3.5 V and 4.0 V

51
Q

what is the composition of a lithium-ion cell?

A

the cell consists of a sandwich of different layers of lithium cobalt oxide and carbon

52
Q

how do lithium ions flow within the cell?

A

when the cell is charged and discharged the lithium ions flow between the negative and the positive through the solid electrolyte

53
Q

what is the memory effect of NiCad cells?

A

they gradually begin to lose their charge after repeated charge cycles when the cell is not fully discharged

the cells appear to ‘remember’ their lower state of charge

54
Q

problems with lithium-ion cells x2

A

current demand of lithium exceeds supply

lithium-ion cell fires, as it is a very reactive element in group 1 (high electrode potential)

55
Q

example uses of electrolysis x4

A

purifying copper

plating metals with silver and gold

extracting reactive metals, such as aluminium

making chlorine, hydrogen and sodium hydroxide

56
Q

how can electrolytic cells be constructed?

A

using a beaker or crucible as the cell depending on whether the ionic compound is in solution or molten

57
Q

watch a video on electrolytic cells

A

-

58
Q

in electrolysis, the substance that the current passes through and splits up is called the _______

A

electrolyte

59
Q

what does an electrolyte contain? x2

A

positive ions
negative ions

60
Q

what happens to negative ions during electrolysis?

A

move to the anode & lose electrons (oxidation)

61
Q

what happens to positive ions during electrolysis?

A

move to the cathode and gain electrons (reduction)

62
Q

what happens to electrically neutral atoms/molecules during electrolysis?

A

they are released

63
Q

since metals are always cations and non-metal anions, it is easy to predict the products of electrolysis of molten salts:
where will metals be formed? where will non-metals be formed?

A

metals will always be formed at the cathode and non-metals at the anode

chemistry (8 decks)

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