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Half Reaction Method, Balancing Redox Reactions In Basic & Acidic Solution, Chemistry

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This video explains and demonstrates the half-reaction method for balancing redox reactions in neutral, acidic, and basic solutions, emphasizing the importance of balancing both atoms and charge.

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in this video we're going to focus on

the half reaction method used to

balance redox reactions

we're going to consider an example

using a neutral solution an acidic

solution and a basic solution

so let's start with a neutral solution

let's say

if aluminum metal

reacts with

nickel plus two

and it produces the aluminum plus three cation

cation

and nickel metal

go ahead and balance

this reaction using the half reaction method

method

now when balancing a redox reaction

you need to make sure that not only the

particles are balanced the atoms and the

ions but also

that you have charge balance the charges

must be balanced on both sides

in this example we have one aluminum

atom and ion on both sides

and we have a nickel particle

on the left and one on the right

so the atoms are balanced but however

the charges are not the left side

contains a net charge of positive two

the right side contains a total charge

of positive three

so this reaction is not balanced yet

so what we're going to do is we're going

to separate it into half reactions

let's start with the first one aluminum

now in order to balance it we'll need to

balance the charge

the net charge on the left is zero the

net charge on the right is three

so the difference between these two

numbers is three we're going to add

three electrons to the side with the

higher charge

and so the first half reaction

is balanced whenever the electrons are

on the right side

this half reaction represents an

oxidation reaction

now let's move on to the second half reaction

reaction

nickel plus two

turns into nickel

now in order to balance the charge we

gotta add two electrons to the left side

so whenever the electrons are on the

left side you have a reduction half reaction

reaction

now before we can add the two half

reactions we need to make sure the

number of electrons are the same on both sides

sides

the least common multiple of two and

three is six

so we need to get six electrons on both

reactions let's multiply the first one

so we're gonna have is two a l

which becomes two a l plus three

plus six electrons

and then below that three

nickel two plus cations plus six electrons

electrons

which becomes uh three nickel atoms

now we're going to add these two half reactions

reactions

notice that the electrons cancel

when that happens

the charges will be balanced

so on the left side we have these two

we have two aluminum atoms

reacting with three

nickel ions

and on the right side

two aluminum cations are being produced

and three nickel atoms

so notice that the number of nickel

particles is the same on both sides

and the number of aluminum particles is

the same

and the total charge is the same on the

left side it's 3 times 2

which is positive six and on the right

side it's two times three which is

positive six

so in balance in a redox reaction you

need to make sure that the number of

atoms are the same on both sides and

also the total charge has to be the same

on both sides

zinc

reacts with bromate

to produce

the zinc cation

balance this reaction under acidic conditions

conditions

under acidic conditions you can add h plus

plus

and water to balance a half reaction

so let's start with zinc

in order to balance this half reaction

all we need to do

now let's move on to the second half reaction

reaction

where bromate

now we already have one bromine atom on

both sides

so the next thing we need to do is

balance the oxygen atoms

and to do that we got to add water

so we need to add three water molecules

to the left side i mean the right side

in order to balance it so we have three

oxygen atoms on both sides

but now

we have six hydrogen atoms on the right side

side

so we need to add six

h plus ions to the left

now that all the atoms are balanced

we need to balance the charges

the net charge on the left side

is negative one

then that charge on the right side

is six

the difference between five and negative

one is six if you take five

and subtract it by negative one this is

equal to six

so therefore we need to add six

electrons now should we add it to the

left side or the right side

you should always add electrons to the

side with the higher total charge

so in this example we're going to add

six electrons

to the left side

and so now the second half reaction is balanced

balanced

now we need to make the number of

electrons equal on both sides so

therefore all we need to do

is multiply the first half reaction by three

three

and so it's going to be three

zinc atoms

producing three zinc ions

and six electrons

so now

we can add the two half reactions

to do so we need to cancel the six

electrons on both sides

and everything else we can bring down

so this is on the left side of the arrow

so we can bring it down

on the left side and then we have these

and on the right side

one bromide ion

so now let's make sure

that everything is balanced in our final answer

answer

so we have one bromine atom on both sides

sides

we have three

zinc particles on both sides

six hydrogen atoms three times two is six

six

and now let's check the total charge the

total charge

on the left side is six plus negative one

one

so it's positive five

on the right side it's three times two

which is six

plus negative one and so that two is

positive 5.

so now the total charge is the same and

the number of particles is the same on

both sides

this

now let's try another example

and let's balance it using the half

reaction method

under basic conditions

you can add hydroxide and water to

balance a half reaction

but it might be difficult to do so

an easier technique is to start by

balancing it under acidic conditions

and then add hydroxide to both sides of

the reaction

so i'll illustrate that with this example

example

so let's start with the first half reaction

reaction aluminum

aluminum produces

produces

now in order to balance the number of

atoms all we need to do is add four

and now the particles are balanced

now we need to balance the charge

the total charge

on the right side is negative one on the

left side it's four times negative one

or negative four

so these two numbers differ by three

now should we add the three electrons to

the left side or to the right side

which number is higher

on a number line negative four or

negative one

negative one is a higher number so we

need to add three electrons to negative

to the right side

so now the charges are balanced the net

charge on the right side is negative one

plus negative three which is negative four

four

so for this one

i'm going to balance it first as if it's

under acidic conditions so i'm going to

add four water molecules

on the right side so that the number of

oxygen atoms

will be the same on both sides so we

have four oxygen atoms on both sides

now i have eight hydrogen atoms on the

right side so i'm going to add eight h

plus ions

under basic conditions

the hydrogen ion is virtually

non-existent so we need to get rid of it

so i'm going to add eight hydroxide ions

when you mix h plus and oh minus you're

gonna get water

so therefore

these two will combine and form eight

on the right side

i'm still gonna have the four water molecules

molecules

but i'm also gonna have eight hydroxide ions

ions

now if you have the same substance on

both sides

you could simplify the equation

let's subtract both sides by four water molecules

and so now we have the balance reaction

under basic conditions eight minus four

is four

so it's four water molecules plus a per

chlorine ion produces one chloride ion

and eight hydroxide ions

so notice that the number of atoms

is balanced in this reaction

we have eight hydrogen atoms

on both sides

and we have eight oxygen atoms on the

right side

we have four from water and four from

the chlorine ion the perchlor ion

now all we need to do

is balance the charges

so the net charge on the left side is

negative one

the total charge on the right side is

negative one plus negative eight or

negative nine so these two numbers

differ by eight and negative one is

higher than negative nine so i'm going

now we need to make the number of

electrons equal

so 3 times 8 is 24.

that's the least common multiple between

3 and 8. so i need to

multiply this reaction by 8 to get 24

electrons and this one by 3 to get 24

electrons as well

so then this is going to be 32

hydroxide ions

plus 8

aluminum atoms

and that produces

plus

now let's move on to this one let's

multiply everything by three

so we're going to have 24 electrons

electrons plus

plus

12 water molecules

plus three perchlorate

ions and that's going to produce

three chloride ions

and 24

so now that we have the same number

of electrons on both sides we can add

the two half reactions

so let's cancel

the number of electrons

and so on the left we have 32 hydroxide ions

ions

plus eight aluminum atoms

12 water molecules

and three perchlorate ions

on the right side

three chloride ions and 24 hydroxide ions

ions

so notice that

we can reduce this reaction because we

have hydroxide on both sides

so what we need to do is subtract both

sides by 24

so the final answer

is going to be 32 minus 24 which is eight

so we have eight hydroxy ions eight

aluminum atoms

12 water molecules

three per chlorate ions

and that yields three chloride ions

and that's about it

now let's make sure that

the reaction is balanced

so we have eight aluminum atoms on both sides

sides

we have three chlorine atoms on both sides

sides

now on the right side we have eight

times four

or 32 hydrogen atoms

on the left side here we have 8 hydrogen atoms

atoms

and 12 times 2 is 24 24 plus 8 is 32

so we got 32 hydrogen atoms on both sides

sides

now for oxygen we have 8 times 4 or 32

oxygen atoms on the right side

here we have 8

this is 12 and 3 times 4 is 12.

so 12 plus 12

plus 8

that's 24

plus 8 which is 32.

now the last thing that we need to do

is check

the charges

so this is 3 times negative 1

plus negative eight so the total charge

on the left side is negative eleven

and here this is eight times negative

one plus negative three

so the total charge on the right side is

negative eleven

so once the number of atoms

and the total charge is the same

on the right side once you have

once the mass is balanced and the

charges are balanced

then the redox reaction is balanced as well

well

so this is the final answer

so now you know how to balance a redox reaction

reaction

using the half reaction method under

neutral solutions acidic solutions and

basic solutions

so that's it for this video that's all i

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YouTube文字起こし：Half Reaction Method, Balancing Redox Reactions In Basic & Acidic Solution, Chemistry

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Half Reaction Method, Balancing Redox Reactions In Basic & Acidic Solution, Chemistry

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