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Chemistry
11 Dec 2025
61
2 pages
Emilie @emi_cxxc
Ever wondered why lemon juice makes your face scrunch up or why soap feels slippery? It's all about... Show more
The pH scale is your roadmap for measuring how acidic or alkaline any solution is. Think of it like a number line from 0 to 14 that tells you exactly what you're dealing with.
Acids have a pH less than 7 and form H⁺ ions when dissolved in water. The more hydrogen ions floating around, the more acidic your solution becomes - and here's the tricky bit - as hydrogen ion concentration increases, the pH number actually decreases!
Bases become alkaline when they're soluble in water, giving you a pH greater than 7 (8-14). These form OH⁻ ions (hydroxide ions) in water, and unlike acids, more hydroxide ions means a higher pH number.
Quick Tip Remember that acids and bases are opposites - acids release H⁺ ions whilst alkalis release OH⁻ ions. When they meet, they neutralise each other!
You can measure pH using indicators - special dyes that change colour at different pH levels. Universal indicator gives you the full rainbow, whilst litmus paper simply goes red for acids and blue for alkalis. Methyl orange and phenolphthalein are other handy indicators you'll use in practical work.
Neutralisation happens when an acid meets a base - it's like a chemical peace treaty! This reaction always produces salt and water, making it one of the most predictable reactions in chemistry.
The basic equation is simple Acid + Base → Salt + Water. For example, hydrochloric acid plus sodium hydroxide gives you sodium chloride (table salt) and water HCl + NaOH → NaCl + H₂O.
At the molecular level, neutralisation is really about hydrogen and hydroxide ions combining. The ionic equation H⁺ + OH⁻ → H₂O shows exactly what's happening - those opposite ions are joining forces to make water.
Key Insight Perfect neutralisation occurs at pH 7, where the concentration of H⁺ ions exactly equals the concentration of OH⁻ ions - it's the perfect chemical balance!
When neutralisation is complete, you'll always end up with a neutral solution (pH 7). This is incredibly useful in real life - from treating acid indigestion with alkaline remedies to treating acidic soil with lime in agriculture.
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.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the pH scale and the behavior of strong acids in aqueous solutions. This summary covers key concepts such as complete dissociation, pH calculations for strong monobasic acids, and the relationship between pH and hydrogen ion concentration. Ideal for OCR A A-Level Chemistry students looking to grasp the fundamentals of acids and bases.
ChemistryExplore the essential techniques of acid-base titrations, including key definitions, step-by-step methods, and calculations for determining unknown concentrations and molar masses. This summary also covers measurement uncertainties and how to effectively record results. Ideal for chemistry students preparing for practical assessments.
ChemistryExplore a comprehensive set of exam questions focused on weak acids and bases, including topics such as acid-base titrations, buffer solutions, and the acid dissociation constant (Ka). This resource is ideal for students preparing for chemistry exams, providing practice on key concepts like pH calculations, neutralization reactions, and the behavior of carboxylic acids.
ChemistryExplore the fundamentals of acid-base chemistry, including conjugate acid-base pairs, the acid dissociation constant (Ka), and the relationship between pKa and pH. This summary covers key calculations for weak acids and strong bases, essential for A-Level Chemistry students. Understand how to determine pH and the significance of Kw in aqueous solutions.
ChemistryExplore essential formulas for calculating pH, including the Henderson-Hasselbalch equation, Ka, and pKa. This summary covers strong and weak acids, buffers, and the ICEE method for pH determination, tailored for A-Level Chemistry students.
ChemistryExplore key concepts in acids, bases, and buffers through detailed practice questions and model answers. This resource covers acid-base titrations, pKa values, conjugate acid-base pairs, and the Henderson-Hasselbalch equation, providing essential calculations and explanations for mastering the topic.
ChemistryApp 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
Emilie
@emi_cxxc
Ever wondered why lemon juice makes your face scrunch up or why soap feels slippery? It's all about acids and bases! Understanding the pH scale and how these substances behave is crucial for your chemistry studies and explains loads of... Show more
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Join milions of students
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The pH scale is your roadmap for measuring how acidic or alkaline any solution is. Think of it like a number line from 0 to 14 that tells you exactly what you're dealing with.
Acids have a pH less than 7 and form H⁺ ions when dissolved in water. The more hydrogen ions floating around, the more acidic your solution becomes - and here's the tricky bit - as hydrogen ion concentration increases, the pH number actually decreases!
Bases become alkaline when they're soluble in water, giving you a pH greater than 7 (8-14). These form OH⁻ ions (hydroxide ions) in water, and unlike acids, more hydroxide ions means a higher pH number.
Quick Tip: Remember that acids and bases are opposites - acids release H⁺ ions whilst alkalis release OH⁻ ions. When they meet, they neutralise each other!
You can measure pH using indicators - special dyes that change colour at different pH levels. Universal indicator gives you the full rainbow, whilst litmus paper simply goes red for acids and blue for alkalis. Methyl orange and phenolphthalein are other handy indicators you'll use in practical work.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Neutralisation happens when an acid meets a base - it's like a chemical peace treaty! This reaction always produces salt and water, making it one of the most predictable reactions in chemistry.
The basic equation is simple: Acid + Base → Salt + Water. For example, hydrochloric acid plus sodium hydroxide gives you sodium chloride (table salt) and water: HCl + NaOH → NaCl + H₂O.
At the molecular level, neutralisation is really about hydrogen and hydroxide ions combining. The ionic equation H⁺ + OH⁻ → H₂O shows exactly what's happening - those opposite ions are joining forces to make water.
Key Insight: Perfect neutralisation occurs at pH 7, where the concentration of H⁺ ions exactly equals the concentration of OH⁻ ions - it's the perfect chemical balance!
When neutralisation is complete, you'll always end up with a neutral solution (pH 7). This is incredibly useful in real life - from treating acid indigestion with alkaline remedies to treating acidic soil with lime in agriculture.
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.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the pH scale and the behavior of strong acids in aqueous solutions. This summary covers key concepts such as complete dissociation, pH calculations for strong monobasic acids, and the relationship between pH and hydrogen ion concentration. Ideal for OCR A A-Level Chemistry students looking to grasp the fundamentals of acids and bases.
ChemistryExplore the essential techniques of acid-base titrations, including key definitions, step-by-step methods, and calculations for determining unknown concentrations and molar masses. This summary also covers measurement uncertainties and how to effectively record results. Ideal for chemistry students preparing for practical assessments.
ChemistryExplore a comprehensive set of exam questions focused on weak acids and bases, including topics such as acid-base titrations, buffer solutions, and the acid dissociation constant (Ka). This resource is ideal for students preparing for chemistry exams, providing practice on key concepts like pH calculations, neutralization reactions, and the behavior of carboxylic acids.
ChemistryExplore the fundamentals of acid-base chemistry, including conjugate acid-base pairs, the acid dissociation constant (Ka), and the relationship between pKa and pH. This summary covers key calculations for weak acids and strong bases, essential for A-Level Chemistry students. Understand how to determine pH and the significance of Kw in aqueous solutions.
ChemistryExplore essential formulas for calculating pH, including the Henderson-Hasselbalch equation, Ka, and pKa. This summary covers strong and weak acids, buffers, and the ICEE method for pH determination, tailored for A-Level Chemistry students.
ChemistryExplore key concepts in acids, bases, and buffers through detailed practice questions and model answers. This resource covers acid-base titrations, pKa values, conjugate acid-base pairs, and the Henderson-Hasselbalch equation, providing essential calculations and explanations for mastering the topic.
ChemistryApp 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