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chem > Redox > Flashcards

Redox Flashcards

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1
Q

what is an electrolyte

A

substance consist of mobile ions and conduct electricity when dissolve in water or melted

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2
Q

why aluminium can reduce Fe3+

A

aluminium is a stronger reducing agent than iron

it loses electrons more readily than iron

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3
Q

how to use chemical cells to obtain the order in ECS

A

use different metals as electrodes in the chemical cells

then arrange the metals according to the voltage obtained

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4
Q

why ECS is similar to metal reactivity series

A

more readily the metal loses electrons, more reactive the metal is.

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5
Q

why copper layer is easily flaked off when hydrogen gas is formed in cathode

A

The hydrogen gas bubbles hinder the deposition of copper on the surface of the metallic object, hence causing the copper metal deposited easily flaked off.

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6
Q

is hydrogen oxygen fuel cell a primary cell

A

yes

it cannot be recharged (充電）

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7
Q

what is the function of the porous pot

A

allow ions to pass through
to complete the circuit
separate electrolytes and prevent direct mixing of them

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8
Q

why the color of phenolphthalein turns to pink after H+ is preferentially discharged

A

as (OH-)> (H+) when H+ ions are consumed

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9
Q

why dilute HNO3 cannot be used to acidify KMnO4 and Na2Cr2O7

A

its because dilute HNO3 itself is an oxidizing agent

it will react with the reducing agent also

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10
Q

what should be used to acidify KMnO4 and Na2Cr2O7

A

dilute H2SO4

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11
Q

why conc HNO3 need to be put in a brown bottle

A

its because conc HNO3 decomposes easily in the presence of sunlight
so the brown bottle is used to cut the sunlight

4HNO3 to 2H2O + O2 +4NO2

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12
Q

conc acid + non-metal (eg C,S)

need heat?

A

YESSSS

need HOT conc acid

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13
Q

can conc acid react with Au and Pt

A

NOOOOOOOOO

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14
Q

what is the colour of S(solid)

A

yellow

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15
Q

is conc H2SO4 both a dehydrating agent and drying agent

A

yes
it can dry neutral and acidic gas
and also dehydrate hydrated compound or carbohydrates

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16
Q

SO2 is…

A

toxic

attack human respiratory system

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17
Q

formula of sucrose

A

C12H22O11

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18
Q

color of iodine

A

purple in solid
purple in organic solvent
brown in water
brown for I- in I2

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19
Q

what should be done to the metal before using them as electrodes in a chemical cell

A

first cleaned with a sand paper to remove any oxide layer on the surface .
This improves the electrical conductivity

20
Q

what does the sign of the voltage means in the test testing the relative reactivity of metals

A

whetehr (copper) electrodes is + or -

21
Q

what is the effect of surface area between the electrode and the electrolyte

A

larger surface area immersed in the electrolyte leads to faster redox reaction –> larger volatge

22
Q

what is the effect of the distance between two electrodes in chemical cell

A

shorter the distance larger the voltage

23
Q

what is the effect of the conc of the electrolyte to the voltage

A

more conc

voltage higher

24
Q

what is the substance in the slat bridge

A

saturated KNO3

25
Q

function of salt bridge

A

complete the circuit by providing mobile ions to conduct electricity
maintain the charge balance

26
Q

when Cl2 is produced in the chemical cell

which inert electrode should not be used

A

platinum Pt

Pt will be attacked readily by Cl2

27
Q

what is charge capacity

A

the quantity of electricity a cell can deliver

28
Q

what is shelf life

A

the duration of storage at the end of which a cell retains only 90% capacity

29
Q

what is service life

A

the period of effective service of a cell before the voltage falls to a certain value

30
Q

why H2 has to be removed in zinc carbon cell

A

it reduce the current of the cell as H2 is non-conducting

it will increase the pressure inside the cell and leads to explosion

31
Q

advantage of using hydrogen-oxygen fuel cell

A 
higher efficiency(convert energy directly from the fuel)
products are non-polluting
voltage does not drop as long as the fuels and oxidizing agents are continuously supplied
32
Q

disadvantage of using hydrogen-oxygen fuel cell

A

expensive

difficult to store hydrogen gas

33
Q

describe the working principle of the fuel cell

A

The principle of the fuel cell is based on the conversion of chemical energy released in the reaction 2H2 +O2 –> 2H2O to electrical energy

In the H2 compartment, H2 is oxidized to H2O
H2 +2 OH- –> 2H2O + 2e-
In the O2 compartment, O2 is reduced to OH-
O2 + 2H2O + 4e- –> 4OH-

the concentration NaOH acts as an electrolyte and provide the OH- ions for the anodic reaction

The electrochemical reaction are catalysed by the Pt electrode in the electrodes

34
Q

what is electrolysis

A

it is the process by which the electrolyte, electrode or water is decomposed by using electricity

35
Q

the redox reaction in chemical cell is

exothermic/endothermic

A

exothermic

36
Q

the redox reaction in electrolytic cell is

exothermic/endothermic

A

endothermic

37
Q

why pure Cu is more desirable than impure Cu

A

pure Cu has a much higher electrical conductivity than impure Cu

38
Q

what is electroplating

A

electroplating is the process to coat a thin layer of metal on an electrical conducting object by elecctrolysis

39
Q

what is the usage of electroplating

A

more corrosion resistant and more attractive appearance

40
Q

how to electrplate a shiny and firm metal layer on the object

A

the object should be first cleaned with sandpaper to acid to remove the metal oxide layer and then alkalis to remove any grease present on it before electroplating

41
Q

what does the effluent (waste water) in electroplating industry contains

A

acid and alkali
cyanides CN-
heavy metal ions

42
Q

what substance can be used to netralize acidic effluent (waste water)

A

Ca(OH)2

Na2CO3

43
Q

what substance can be used to remove heavy metal ions

A

NaOH
Na2CO3
to precipitate followed by fitration

44
Q

what is the essential feature of redox reaction

A

a reaction involving a transfer of electrons from one reactant to another

45
Q

what is the role of NH4Cl in zinc-carbon cell

A

electrolyte

46
Q

can NH3 be a reducing agent

A

yes
NH3 to N2
form -3 to 0

47
Q

why is it necessary to remove cu2+ in waste water

A

to recover copper metal

cu2+ can cause water pollution

chem (14 decks)

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