Electrochemistry

Question 1

oxidation is ___________?
reduction is __________?

Answer 1

loss of electrons & hydrogen atom & gain of oxygen atom.
gain of electrons & hydrogen atom & loss of oxygen atom.

remember it in this way: if u lose H atom u lose an electron

OIL RIG in terms of electrons

Question 2

oxidation is _____ of hydrogen atom.
electrochemical processess always involve ___________.

Answer 2

loss
transfer of electrons or redox reactions.

Question 3

elements from group __________ undergo oxidation.

Answer 3

IA
IIA
IIIA

oxidations is loss of electrons.

they have 1 to 4 e in valence shell, thus losing electrons to form cations

Question 4

elements from which group undergoes reduction?

Answer 4

VA
VIA
VIIA

reduction is gain of electrons.

they have 5 to 7 e in valence shell, thus gaining electrons to form anions.

Question 5

how to know which element is being oxidized?

Answer 5

know which is metal or non-metal
know their atomic no.
check who gains or loses oxygen or hydrogen.

Question 6

define oxidation state?

Answer 6

the number of charges an atom will have in a molecule or compound.

aka oxidation number

Question 7

give oxidation states of elements in periodic table?

Answer 7

group IA=+1
IIA=+2
IIIA= +3
VIIA= -1
VIIIA=0

Question 8

oxidation number of F?
H?
O?

Answer 8

-1
H with metals: -1(as metal lose electron to H)
H with non-metals: +1 ( as non-metal gain e from H)
-2 except peroxides & with fluorine

these only happen in binary compounds or else every1 has 0 oxidation no.

Question 9

what is oxidizing agent? what oxidation state do they have?

Answer 9

the reactant conatining the element that is reduced in a chemical reaction.
gains electrons and is reduced in a chemical reaction
they have high oxidation state

loss of e = oxidation

the Substances that have the Ability to Oxidize other Substances by Accepting Electrons From Them.

Question 10

what is reducing agent?

Answer 10

the reactant conatining the element that is oxidized in a chemical reaction.

the Substances that Have the Ability to reduce other Substances by giving Electrons to Them.

Question 11

how to identify oxidizing & reducing agents?

Answer 11

1. workout the oxidation states of all the elements involved in the reaction.
2. note the element that is going an increase in its oxidation state. Since it is being oxidized. The reactant that contains this element is reducing agent.
3. note the element that is undergoing a decrease in its oxidation state. Since it is being reduced, the reactant that contains this elements is oxidising agent.

Question 12

what does oxidation no. tell us?

Answer 12

The oxidation number of an atom in a chemical compound is a measure of the degree of oxidation (loss of electrons) of that atom. It is a concept used to keep track of electron transfer in chemical reactions.
+ve oxidation no. : the atom has lost electrons (oxidation).
-ve oxidation no. : the atom has gained electrons (reduction).

Question 13

oxidation number for F?
elements of 7A?

Answer 13

0
not -1 because the rules should be followed hierarchy.
Fluorine will have -1 oxidation no. only when it is with other molecule.
when fluorine is alone, it will have 0.
-1

Question 14

in a blast furnace:
what is used as reducing agents?
why?
what is a slag?
how is it formed?
how do we recover zinc & lead from their sulphide ores?

Answer 14

Al, coke, CO, Hydrogen gas
to reduce the metal (loss of O atom from metal)
impurities from iron ore
CaCO3 removes it which is added from top.
first convert the ores into oxides by heating in Oxygen. sulphur is oxidized (gain O atom) (SO2) & oxygen (O2) (loss O atom from itself) is reduced. (O)
then oxides are reduced by C, CO, H

Question 15

what is electrolyte?
anode & cathode has _____charge.
nelson’s cell is used for __________.
down’s cell is used for _________.
all electrolytic cells operate in a ____________.
all galvanic cells operate in a ____________.

Answer 15

substance that conducts electricity when it is dissolved in water or in the molten state.
+ -
commercial preparation of NaOH produces chlorine and hydrogen gas as by product
commercial preparation of sodium metal chlorine gas as by product
non-spontaneous manner
spontaneous manner

Question 16

_______ occurs at anode
_______ occurs at cathode
daniel cell aka?
uses of electrolytic cells?

Answer 16

oxidation
reduction
galvanic cells
Electroplating: electroplating of zinc, tin & chromium on steel.

Electrorefining: electrolytic refining of Cu.

Electrolysis of water: for production of H2 gas.

Electrolytic production of chemicals: manufacture of NaOH from brine & Na metal from fused NaCl.

Question 17

an electrolytic cells consists of?

Answer 17

1. a vessel containing electrolyte
2. two inert electrodes
3. a battery

Question 18

a galvanic cell consists of?
draw one?

w/ purposes

Answer 18

1. a voltmeter: to measure current
2. salt bridge: inverted U tube containing an inert electrolyte such as KCl. Its ions doesn’t react w/ electrode or with the ions in solution. it makes the electrical contact through which ions move b/w the solution.

Question 19

define a battery? examples?

Answer 19

a galvanic cell or a group of galvanic cells joined in series. it generates electric current by redox reactions
examples: dry cell, storage cell & mercury battery etc.

Question 20

Na metal

what is placed at anode & cathode?
where do ions move?
what happens at the electrodes to gain Na metal?
what electrolyte is used?
which cell is used?
is there any by product?

answer with reasons

Answer 20

iron cathode
graphite (C) anode
pg 141
fused or molten NaCl
down’s cell (electrolytic cell)
chlorine

Question 21

NaOH

what is at anode & cathode to produce NaOH from _________?
what happens at the electrodes to gain NaOH? state overall reaction?
what electrolyte is used?
which cell is used?
is there any by product?
why Na ions don’t reduce (give e-) to Na metal when they move towards cathode?

answer with reasons

Answer 21

Na ions move towards cathode and Cl ions move towards anode.
brine (concentrated aqueous solution of NaCl)
pg 141
brine (NaCl)
nelson’s cell (electrolytic cell)
chlorine & hydorgen gas
cz H2O molecules can be more easily reduced than Na ions

Reason: Cathode is a negatively charged electrode and therefore attracts Na+ions. Anode is a positively charged electrode and therefore attracts Cl− ions.

Question 22

refining of Cu

what is used as anode & cathode?
what happens at the electrodes to gain pure Cu?
why does Cu lose e- at the first place?
pure Cu deposits at ______. why?
what electrolyte is used?
which cell is used?
is there any by product?

answer with reasons

Answer 22

impure copper anode
pure copper cathode
pg 142
anode + so e- attract + anode so Cu lose e-
cathode (-) Cu+2 + 2e- = Cu (s)
as electrons flow towards cathode
CuSO4 w/ little H2SO4
electrolytic cell
no

Question 23

the plating material is made _____
the object to be electroplated is made _____
in Zn plating, which electrolyte is used?
why is it used?
how does the electrolyte ionizes? chemical reaction?
what reactions happen at anode & cathode?

Answer 23

anode (+)
cathode (-)
zinc cyanide little Na cyanide
K2 {Zn (CN)4}
to prevent hydrolysis of electrolyte

chemical breakdown of a compound due to reaction with H2O.

Question 24

in tin plating, which electrolyte is used?
why is it used?
how does the electrolyte ionizes? chemical reaction?
what reactions happen at anode & cathode?
tin is used at _______.

Answer 24

SnSO4 (stannous sulphate)
dil H2SO4
to prevent hydrolysis of electrolyte
anode (+) oxidation happens at anode

Question 25

in chromium plating, which electrolyte is used?
why is it used?
how does the electrolyte ionizes? chemical reaction?
what reactions happen at anode & cathode?
what is used as anode?
why steel is first plated with _______?

Answer 25

chromium sulphate Cr2(SO4)3
dil H2SO4
Cr is at anode
Cu electroplated steel at cathose

chromium metal
Cu or nickel because Cr metal does not adhere strongly to the Steel therefore steel is first plated with Cu or nickel.

Copper is soft & attaches itself very well to things harder than itself, such as steel & Cr. Very few plating materials stick to steel well besides Cu.

Question 26

electrolytic process?
what is electroplating?

Answer 26

process of using electricity to drive a chemical reaction, typically involving the decomposition of a compound into its constituent elements or ions.
electrolytic process used to deposit one metal on another metal.

electrolytic process = electrolysis

Question 27

what is corrosion​?

Answer 27

a natural process in which a metal reacts with oxygen & moisture (water) in the atmosphere. it converts refined metals into more stable metal oxides.

a metal that has been purified

Question 28

in rusting of iron why would iron lose electrons?

Answer 28

to get stable from refined to stable oxide
when iron reacts with oxygen in the presence of water, iron atoms lose electrons to form iron ions (Fe2+) &
oxygen atoms gain electrons to form oxide ions (O2-).

Question 29

in rusting of iron what would happen at anode & cathode? reactions? state the formula of rust?

Answer 29

a region of metal with less moisture is anode
a region of metal with more moisture is cathode.
at anode Fe(s) → Fe+2 (aq) + 2e-
at cathode Fe +2 ions further react with oxygen to form rust.
rust = Fe2O3 . x H2O

O2 + 2H2O + 4e- → 4OH-

Question 30

why aircraft do not corrode even if it is made up of aluminium & aluminium has more tendency to oxidize than iron?

Answer 30

Aluminium is more reactive than Iron but is less corrosive when exposed to air: Aluminium forms a natural layer of Al2O3 when exposed to air. This layer prevents the underneath metals to come in contact with air.

Question 31

how to prevent corrosion?

Answer 31

pg 144

Question 32

how are voltaic cells & electrolytic cells different?

Answer 32

Electron Flow:

In a voltaic cell, spontaneous chemical reactions generate an electric current. Electrons flow from the anode to the cathode through an external circuit.

In an electrolytic cell, an external power source (such as battery or a direct current power supply) drives the non-spontaneous electron flow, forcing electrons to move in the opposite direction.

Purpose:

Voltaic cells are used to generate electricity. They are common in batteries, where chemical reactions produce electrical energy.
Electrolytic cells are used for processes like electroplating, electrolysis of water, and extraction of metals from their ores. They require an external power source to drive the non-spontaneous reactions.

Products:

In a voltaic cell, the products of the spontaneous redox reaction are typically useful chemical compounds or electrical energy.
In an electrolytic cell, the products depend on the specific process but often include elements or compounds separated from the electrolyte.

Question 33

how are voltaic cells & electrolytic cells alike?

Answer 33

Similarities:
​
Electrodes: Both types of cells have 2 electrodes, an anode (where oxidation occurs) & a cathode (where reduction occurs).
​
Electrolytes: Both cells contain electrolytes, which are substances that allow ions to move between the electrodes to balance charge during the electrochemical reactions.
​
Redox Reactions: Both cells involve redox (reduction-oxidation) reactions. In a redox reaction, one substance loses electrons (oxidation) while another gains electrons (reduction).