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Britain & the wider world: 1745 -1901
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16 Dec 2025
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Electrolysis might sound complex, but it's essentially about moving electrons... Show more
Ever wondered how atoms become charged? It's all about electron transfer, and once you get the pattern, it becomes straightforward.
When metals like lithium (Li⁺) or magnesium (Mg²⁺) have positive charges, they need to gain electrons to become neutral atoms again. The number tells you exactly how many electrons they need - Li⁺ gains one electron, whilst Mg²⁺ gains two electrons.
Non-metals work the opposite way. Chloride ions (Cl⁻) and oxide ions (O²⁻) have negative charges because they have extra electrons. To become neutral atoms, they must lose electrons - chloride loses one, oxide loses two.
Quick Tip: The number in the charge always tells you exactly how many electrons are gained or lost!
During electrolysis, positive ions head to the negative electrode (cathode) where they pick up the electrons they need. It's like opposite charges attracting - the aluminium ions (Al³⁺) grab three electrons to become aluminium metal.
Writing half equations becomes easy when you remember two key rules: balance the atoms and balance the charge.
Don't forget that many non-metals exist as diatomic molecules - Cl₂, Br₂, I₂, O₂, and H₂. This means you'll often need to double up your ions to make the equation work properly.
At the cathode (negative electrode), positive ions gain electrons. For example: Mg²⁺ + 2e⁻ → Mg. The electrons always appear on the left side because they're being added to the ion.
Remember: Cathode = positive ions gaining electrons, Anode = negative ions losing electrons!
At the anode (positive electrode), negative ions lose electrons. For chloride: 2Cl⁻ → Cl₂ + 2e⁻. Notice how we need two chloride ions to make one chlorine molecule, and the electrons appear on the right because they're being removed.
OIL RIG is your best friend for remembering electron movement: Oxidation Is Loss, Reduction Is Gain (of electrons).
Every half equation shows either oxidation or reduction happening. At the cathode, ions like Ca²⁺ + 2e⁻ → Ca show reduction because electrons are gained. At the anode, reactions like 2Br⁻ → Br₂ + 2e⁻ show oxidation because electrons are lost.
Balancing becomes straightforward once you know the pattern. Count the charges on both sides - they must be equal. If Ca²⁺ needs to become Ca, it needs exactly 2 electrons to balance the 2+ charge.
Pro Tip: Always check your balanced equation - the total charge on the left must equal the total charge on the right!
The challenge questions test whether you truly understand the process. For potassium oxide electrolysis, K⁺ ions go to the cathode (gaining 1 electron each), whilst O²⁻ ions head to the anode (losing electrons to form oxygen gas).
Now you can tackle any electrolysis problem by breaking it down into simple steps.
For calcium oxide electrolysis, start by identifying what happens where. Calcium ions (Ca²⁺) are positive, so they're attracted to the negative cathode. There, each ion gains exactly two electrons to become a neutral calcium atom.
Writing the half equations becomes systematic. At the cathode: Ca²⁺ + 2e⁻ → Ca. At the anode, oxide ions lose electrons: 2O²⁻ → O₂ + 4e⁻. Notice how we need two oxide ions to make one oxygen molecule.
Success Strategy: Always identify the charges first, then work out how many electrons are needed to balance!
Finally, identify oxidation and reduction using OIL RIG. The oxide ions lose electrons (oxidation), whilst the calcium ions gain electrons (reduction). Every electrolysis involves both processes happening simultaneously at different electrodes.
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Quotes from every main character
English LiteratureApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Electrolysis might sound complex, but it's essentially about moving electrons around to break down compounds. You'll master half equations by understanding which particles gain or lose electrons and how to balance these reactions properly.
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Ever wondered how atoms become charged? It's all about electron transfer, and once you get the pattern, it becomes straightforward.
When metals like lithium (Li⁺) or magnesium (Mg²⁺) have positive charges, they need to gain electrons to become neutral atoms again. The number tells you exactly how many electrons they need - Li⁺ gains one electron, whilst Mg²⁺ gains two electrons.
Non-metals work the opposite way. Chloride ions (Cl⁻) and oxide ions (O²⁻) have negative charges because they have extra electrons. To become neutral atoms, they must lose electrons - chloride loses one, oxide loses two.
Quick Tip: The number in the charge always tells you exactly how many electrons are gained or lost!
During electrolysis, positive ions head to the negative electrode (cathode) where they pick up the electrons they need. It's like opposite charges attracting - the aluminium ions (Al³⁺) grab three electrons to become aluminium metal.
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Improve your grades
Join milions of students
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Writing half equations becomes easy when you remember two key rules: balance the atoms and balance the charge.
Don't forget that many non-metals exist as diatomic molecules - Cl₂, Br₂, I₂, O₂, and H₂. This means you'll often need to double up your ions to make the equation work properly.
At the cathode (negative electrode), positive ions gain electrons. For example: Mg²⁺ + 2e⁻ → Mg. The electrons always appear on the left side because they're being added to the ion.
Remember: Cathode = positive ions gaining electrons, Anode = negative ions losing electrons!
At the anode (positive electrode), negative ions lose electrons. For chloride: 2Cl⁻ → Cl₂ + 2e⁻. Notice how we need two chloride ions to make one chlorine molecule, and the electrons appear on the right because they're being removed.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
OIL RIG is your best friend for remembering electron movement: Oxidation Is Loss, Reduction Is Gain (of electrons).
Every half equation shows either oxidation or reduction happening. At the cathode, ions like Ca²⁺ + 2e⁻ → Ca show reduction because electrons are gained. At the anode, reactions like 2Br⁻ → Br₂ + 2e⁻ show oxidation because electrons are lost.
Balancing becomes straightforward once you know the pattern. Count the charges on both sides - they must be equal. If Ca²⁺ needs to become Ca, it needs exactly 2 electrons to balance the 2+ charge.
Pro Tip: Always check your balanced equation - the total charge on the left must equal the total charge on the right!
The challenge questions test whether you truly understand the process. For potassium oxide electrolysis, K⁺ ions go to the cathode (gaining 1 electron each), whilst O²⁻ ions head to the anode (losing electrons to form oxygen gas).
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Now you can tackle any electrolysis problem by breaking it down into simple steps.
For calcium oxide electrolysis, start by identifying what happens where. Calcium ions (Ca²⁺) are positive, so they're attracted to the negative cathode. There, each ion gains exactly two electrons to become a neutral calcium atom.
Writing the half equations becomes systematic. At the cathode: Ca²⁺ + 2e⁻ → Ca. At the anode, oxide ions lose electrons: 2O²⁻ → O₂ + 4e⁻. Notice how we need two oxide ions to make one oxygen molecule.
Success Strategy: Always identify the charges first, then work out how many electrons are needed to balance!
Finally, identify oxidation and reduction using OIL RIG. The oxide ions lose electrons (oxidation), whilst the calcium ions gain electrons (reduction). Every electrolysis involves both processes happening simultaneously at different electrodes.
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Quotes from every main character
English LiteratureApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Sociology