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Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
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2d religious conflict and the church in england, c1529-c1570
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1c the tudors: england, 1485-1603
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Lilia Steadman
10/12/2025
Chemistry
Electrochemistry chemistry higher edexcel GCSE summary page
329
•
10 Dec 2025
•
Lilia Steadman
@liliasteadman_
Electrolysis is a fascinating chemical process that splits ionic compounds... Show more
Electrolysis is the process that breaks down ionic substances (called electrolytes) using an electric current. Think of it as using electricity to force chemical reactions that wouldn't normally happen on their own.
The setup involves two electrodes - the cathode (negative) and anode (positive). During electrolysis, positively charged ions (cations) are attracted to the negative cathode, whilst negatively charged ions (anions) head to the positive anode.
Here's the key bit: at the cathode, cations gain electrons (this is called reduction). At the anode, anions lose electrons (called oxidation). Remember this pattern - it's crucial for understanding what products you'll get from any electrolysis reaction.
💡 Quick Tip: Metal ions are always cations, and non-metal ions are anions - except hydrogen, which is a non-metal cation!
When you electrolyse molten ionic compounds, the process is quite straightforward because there's no water to complicate things. Take molten lead bromide (PbBr₂) as an example.
The lead ions (Pb²⁺) move to the cathode where they gain electrons to form pure lead metal. Meanwhile, bromide ions (Br⁻) travel to the anode where they lose electrons and form bromine gas.
Half equations tell you exactly what happens at each electrode. They're like mini-stories showing how ions gain or lose electrons to become discharged (turned into neutral substances).
💡 Remember: In molten electrolysis, you'll always get the metal at the cathode and the non-metal at the anode.
Things get more interesting when you electrolyse solutions because water produces its own ions (H⁺ and OH⁻) that compete with the original compound's ions.
At the cathode, if the metal is more reactive than hydrogen, you'll get hydrogen gas bubbling off instead of the metal. Only less reactive metals (like copper) will actually form at the cathode.
At the anode, halide ions (like Cl⁻ or Br⁻) will form halogen gases if present. If there are no halide ions, you'll get oxygen gas and water instead.
💡 Key Example: Electrolysing sodium chloride solution gives you hydrogen gas at the cathode and chlorine gas at the anode - not sodium metal!
Electrochemical cells work like the reverse of electrolysis - they use chemical reactions to generate electricity rather than using electricity to force reactions. They consist of two half-cells connected by a salt bridge.
Hydrogen fuel cells are particularly clever. They combine hydrogen and oxygen to produce water, electricity, and nothing else harmful. The hydrogen molecules split into ions and electrons, with electrons flowing through an external circuit to create current.
These fuel cells are brilliant because they're renewable and don't produce greenhouse gases. However, they're still expensive to make and often require fossil fuels to produce the hydrogen in the first place.
💡 Future Energy: Fuel cells could power cars and homes cleanly, but the technology needs to become more cost-effective first.
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.
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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
Lilia Steadman
@liliasteadman_
Electrolysis is a fascinating chemical process that splits ionic compounds using electricity - and it's everywhere from metal refining to the batteries in your phone! Understanding how ions move and react at electrodes will help you master one of chemistry's... Show more
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Electrolysis is the process that breaks down ionic substances (called electrolytes) using an electric current. Think of it as using electricity to force chemical reactions that wouldn't normally happen on their own.
The setup involves two electrodes - the cathode (negative) and anode (positive). During electrolysis, positively charged ions (cations) are attracted to the negative cathode, whilst negatively charged ions (anions) head to the positive anode.
Here's the key bit: at the cathode, cations gain electrons (this is called reduction). At the anode, anions lose electrons (called oxidation). Remember this pattern - it's crucial for understanding what products you'll get from any electrolysis reaction.
💡 Quick Tip: Metal ions are always cations, and non-metal ions are anions - except hydrogen, which is a non-metal cation!
When you electrolyse molten ionic compounds, the process is quite straightforward because there's no water to complicate things. Take molten lead bromide (PbBr₂) as an example.
The lead ions (Pb²⁺) move to the cathode where they gain electrons to form pure lead metal. Meanwhile, bromide ions (Br⁻) travel to the anode where they lose electrons and form bromine gas.
Half equations tell you exactly what happens at each electrode. They're like mini-stories showing how ions gain or lose electrons to become discharged (turned into neutral substances).
💡 Remember: In molten electrolysis, you'll always get the metal at the cathode and the non-metal at the anode.
Things get more interesting when you electrolyse solutions because water produces its own ions (H⁺ and OH⁻) that compete with the original compound's ions.
At the cathode, if the metal is more reactive than hydrogen, you'll get hydrogen gas bubbling off instead of the metal. Only less reactive metals (like copper) will actually form at the cathode.
At the anode, halide ions (like Cl⁻ or Br⁻) will form halogen gases if present. If there are no halide ions, you'll get oxygen gas and water instead.
💡 Key Example: Electrolysing sodium chloride solution gives you hydrogen gas at the cathode and chlorine gas at the anode - not sodium metal!
Electrochemical cells work like the reverse of electrolysis - they use chemical reactions to generate electricity rather than using electricity to force reactions. They consist of two half-cells connected by a salt bridge.
Hydrogen fuel cells are particularly clever. They combine hydrogen and oxygen to produce water, electricity, and nothing else harmful. The hydrogen molecules split into ions and electrons, with electrons flowing through an external circuit to create current.
These fuel cells are brilliant because they're renewable and don't produce greenhouse gases. However, they're still expensive to make and often require fossil fuels to produce the hydrogen in the first place.
💡 Future Energy: Fuel cells could power cars and homes cleanly, but the technology needs to become more cost-effective first.
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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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