# Half equations for electrolysis.

Watch
Announcements

Please can anyone teach me how to do them. Im really stuckkkk

Thanks xx

Thanks xx

0

reply

Report

#2

I'm not a great teacher but I'll try explain.

Basically, Electrolysis breaks down the compound into its elements.

So if we Potassium Chloride broken down it would make Potassium and Chlorine. The Potassium ions are positively charged so they go to the cathode to gain electrons and become stable and so the equation would be:

2K+ + 2e- (arrow) 2K , this means that two positively charged potassium ions gain two electrions (reason for the plus) to become stable potassium atoms.

The chlorine ion is negatively charge so it is attracted to the anode. The lose electrons to become stable chlorine atoms so the equation is:

2Cl- - 2e- (arrow) Cl2 , this means that two negatively charged chlorine ions lose two electrions (reason for the minus sign) to become stable chlorine atoms.

If you need more help with it just ask, hope I was of any use.

Basically, Electrolysis breaks down the compound into its elements.

So if we Potassium Chloride broken down it would make Potassium and Chlorine. The Potassium ions are positively charged so they go to the cathode to gain electrons and become stable and so the equation would be:

2K+ + 2e- (arrow) 2K , this means that two positively charged potassium ions gain two electrions (reason for the plus) to become stable potassium atoms.

The chlorine ion is negatively charge so it is attracted to the anode. The lose electrons to become stable chlorine atoms so the equation is:

2Cl- - 2e- (arrow) Cl2 , this means that two negatively charged chlorine ions lose two electrions (reason for the minus sign) to become stable chlorine atoms.

If you need more help with it just ask, hope I was of any use.

1

reply

Report

#3

(Original post by

I'm not a great teacher but I'll try explain.

Basically, Electrolysis breaks down the compound into its elements.

So if we Potassium Chloride broken down it would make Potassium and Chlorine. The Potassium ions are positively charged so they go to the cathode to gain electrons and become stable and so the equation would be:

2K+ + 2e- (arrow) 2K , this means that two positively charged potassium ions gain two electrions (reason for the plus) to become stable potassium atoms.

The chlorine ion is negatively charge so it is attracted to the anode. The lose electrons to become stable chlorine atoms so the equation is:

2Cl- - 2e- (arrow) Cl2 , this means that two negatively charged chlorine ions lose two electrions (reason for the minus sign) to become stable chlorine atoms.

If you need more help with it just ask, hope I was of any use.

**kai4321**)I'm not a great teacher but I'll try explain.

Basically, Electrolysis breaks down the compound into its elements.

So if we Potassium Chloride broken down it would make Potassium and Chlorine. The Potassium ions are positively charged so they go to the cathode to gain electrons and become stable and so the equation would be:

2K+ + 2e- (arrow) 2K , this means that two positively charged potassium ions gain two electrions (reason for the plus) to become stable potassium atoms.

The chlorine ion is negatively charge so it is attracted to the anode. The lose electrons to become stable chlorine atoms so the equation is:

2Cl- - 2e- (arrow) Cl2 , this means that two negatively charged chlorine ions lose two electrions (reason for the minus sign) to become stable chlorine atoms.

If you need more help with it just ask, hope I was of any use.

1

reply

Report

#4

(Original post by

I don't think you need 2K, just K is fine. With Cl you do need the 2 as it is diatomic.

**DaveJ**)I don't think you need 2K, just K is fine. With Cl you do need the 2 as it is diatomic.

0

reply

Report

#6

How do you know whether it will go to the anode or cathode? And also, why does is become Cl2, I thought it would just be Cl?

1

reply

Report

#7

(Original post by

How do you know whether it will go to the anode or cathode? And also, why does is become Cl2, I thought it would just be Cl?

**Ooo'Yeah**)How do you know whether it will go to the anode or cathode? And also, why does is become Cl2, I thought it would just be Cl?

Positive cation to negative cathode.

Negative anion to positive anode.

It becomes Cl2 because Chlorine is diatomic and so cannot exist as Cl.

0

reply

Report

#8

Thank you!

But how do you know if it's postive or negative? Because I thought it could only be that if it lost or gained electrons, how do you know this?

I bet it's a really obvious answer, but I really don't get it atm

But how do you know if it's postive or negative? Because I thought it could only be that if it lost or gained electrons, how do you know this?

I bet it's a really obvious answer, but I really don't get it atm

0

reply

Report

#9

(Original post by

Thank you!

But how do you know if it's postive or negative? Because I thought it could only be that if it lost or gained electrons, how do you know this?

I bet it's a really obvious answer, but I really don't get it atm

**Ooo'Yeah**)Thank you!

But how do you know if it's postive or negative? Because I thought it could only be that if it lost or gained electrons, how do you know this?

I bet it's a really obvious answer, but I really don't get it atm

Well from what I remember, you'll be splitting up an ionic compound. The metal ion will be the cation (loses electrons to bond ionically), and the non-metal ion will be the anion (gains electrons to bond ionically).

0

reply

Report

#11

(Original post by

Ohh okay, so is one always a metal ion?

Sorry for all the questions!

**Ooo'Yeah**)Ohh okay, so is one always a metal ion?

Sorry for all the questions!

Tends to be in ionic compounds.

But it doesn't really matter - the atom which has lost electrons is the positive cation, the atom which has gained electrons is the negative anion.

0

reply

Report

#12

Thank you very, very much! You have cleared up what I have been trying to figure out all week

0

reply

Report

#13

**Cat**ions are

**pussy**tive.

Therefore they will go to the cathode.

Knowing that cations are postive, you know that the anions are negative, and therefore the anode is postive.

2

reply

Report

#14

Right... im stuck also.. i understand all you've said.. but what i dont get is how to like make up your own half equations... for example... "Silver Nitrate was electrolyzed for 40 minutes using a current of 0.2 amps."

a. Write the half equation for the reaction at the negative electrode (cathode)

b. Write the half equation for the reaction at the positive electrode (anode)

ALSO... can someone explain to me about coulombs and faradays please.. i dont understand that AT ALL ..thank you all xx

a. Write the half equation for the reaction at the negative electrode (cathode)

b. Write the half equation for the reaction at the positive electrode (anode)

ALSO... can someone explain to me about coulombs and faradays please.. i dont understand that AT ALL ..thank you all xx

1

reply

Report

#15

(Original post by

Right... im stuck also.. i understand all you've said.. but what i dont get is how to like make up your own half equations... for example... "Silver Nitrate was electrolyzed for 40 minutes using a current of 0.2 amps."

a. Write the half equation for the reaction at the negative electrode (cathode)

b. Write the half equation for the reaction at the positive electrode (anode)

ALSO... can someone explain to me about coulombs and faradays please.. i dont understand that AT ALL ..thank you all xx

**OllieM**)Right... im stuck also.. i understand all you've said.. but what i dont get is how to like make up your own half equations... for example... "Silver Nitrate was electrolyzed for 40 minutes using a current of 0.2 amps."

a. Write the half equation for the reaction at the negative electrode (cathode)

b. Write the half equation for the reaction at the positive electrode (anode)

ALSO... can someone explain to me about coulombs and faradays please.. i dont understand that AT ALL ..thank you all xx

Silver nitrate solution = silver ions, nitrate ions, hydrogen ions and hydroxide ions (these last two from the water)

Ag

^{+}, H

^{+}, NO

_{3}

^{-}, OH

^{-}

There is competition between the two positive ions at the cathode:

Ag

^{+}, H

^{+}

The most reactive ION gets to gain the electrons. In this case it is the silver ion:

Ag

^{+}+ 1e --> Ag(s)

At the anode

-------------

Competition between NO

_{3}

^{-}and OH

^{-}to release electrons. The OH- wins.

4OH

^{-}- 4e --> 2H

_{2}O + O

_{2}

----------------------------------------------------------

You are probably asking at this point how I know which ion gets to react at each electrode. This is something that you must learn.

At cathode: The more unreactive element gets released (it has the more reactive ion). Ions of elements higher up the reactivity series than hydrogen are not released, hydrogen is instead.

At anode: The order of ion reactivity is halide > hydroxide > all others

Therefore in ordinary solutions containing halide ions the halogen is released (unless it's fluorine, which can't get released as it oxidises water). In very dilute halide ion concentrations the hydroxide ions are oxidised and oxygen is released (see the equation above and learn it).

In solutions with all other negative ions hydroxide ions are released (that's why you are better off learning the equation)

---------------------------------------------------------------

The actual amount of a substance released depends on the number of moles of electrons:

Ag+ + 1e --> Ag

This equation tells me that 1 mole of electrons (1e) releases 1 mole of silver.

Moles of electrons = 96348 Coulombs of charge and 1 Coulomb = 1 amp of current per second.

Hence Coulombs = Current x time

Moles of electrons (Faradays) = Coulombs /96485

0

reply

Report

#16

Actually... can you help me with this also...

" Find the mass of zinc liberated if 6 amps flows for 20 minutes during the electrolysis of zinc chloride, ZnCl2." (the 2 is small tho haha)

Thank you very muuuch... x

" Find the mass of zinc liberated if 6 amps flows for 20 minutes during the electrolysis of zinc chloride, ZnCl2." (the 2 is small tho haha)

Thank you very muuuch... x

0

reply

Report

#17

(Original post by

Actually... can you help me with this also...

" Find the mass of zinc liberated if 6 amps flows for 20 minutes during the electrolysis of zinc chloride, ZnCl2." (the 2 is small tho haha)

Thank you very muuuch... x

**OllieM**)Actually... can you help me with this also...

" Find the mass of zinc liberated if 6 amps flows for 20 minutes during the electrolysis of zinc chloride, ZnCl2." (the 2 is small tho haha)

Thank you very muuuch... x

2. The number of moles of electrons = charge /96485

The equation is Zn

^{2+}+ 2e --> Zn(s)

3. So 2 moles of electrons makes 1 mole of zinc...

see if you can figure it out from this.

0

reply

Report

#18

OK... so it would be...

Charge = amps x time (seconds)

Charge = 6 x 1200 = 7200

Number of Electron moles = (7200/96485)

= 0.075 (2s.f)

What do i do now?? thanks btw

Charge = amps x time (seconds)

Charge = 6 x 1200 = 7200

Number of Electron moles = (7200/96485)

= 0.075 (2s.f)

What do i do now?? thanks btw

0

reply

Report

#19

(Original post by

OK... so it would be...

Charge = amps x time (seconds)

Charge = 6 x 1200 = 7200

Number of Electron moles = (7200/96485)

= 0.075 (2s.f)

What do i do now?? thanks btw

**OllieM**)OK... so it would be...

Charge = amps x time (seconds)

Charge = 6 x 1200 = 7200

Number of Electron moles = (7200/96485)

= 0.075 (2s.f)

What do i do now?? thanks btw

Zn

^{2+}+ 2e --> Zn(s)

Therefore as you have 0.0746 molesof electrons you can only form 0.0746/2 moles of zinc.

Mass of zinc = moles x relative atomic mass

0

reply

Report

#20

At this point im still a bit confuse. So half equation is basically writing an equation for 1 side of the electrodes. But why is it like this 2Cl---> Cl2+2e- instead of Cl2+2e- ----> 2cl. At this loint im really confused by that

0

reply

X

### Quick Reply

Back

to top

to top