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18 Jan 2026
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Understanding Acids and Bases - National 4 Chemistry
A
Alex
@mastermind12362
1 / 5
Understanding the pH Scale
The pH scale is like a measuring stick for how acidic or alkaline something is, running from 0 to 14. Think of it as a chemistry thermometer that tells you whether something will be sour (acidic) or bitter (alkaline).
Acids have a pH less than 7 - the lower the number, the more acidic it is. Alkalis (also called bases) have a pH greater than 7, and pure water sits right in the middle at exactly 7, which we call neutral.
Here's a clever trick to remember which oxides make acids or alkalis: soluble metal oxides create alkaline solutions when dissolved in water, whilst soluble non-metal oxides produce acidic solutions. If an oxide doesn't dissolve (it's insoluble), it won't change the water's pH at all.
Quick Tip: Use your data booklet to check if an oxide is from a metal or non-metal, then check its solubility - this tells you exactly what it'll do to pH!
Acids and Alkalis in Daily Life
You encounter acids and alkalis every single day without realising it! Your fizzy drinks, fruit juices, and even the vinegar in your kitchen are all acidic substances that would score below 7 on the pH scale.
In chemistry labs, the main acids you'll work with include sulfuric acid, nitric acid, and hydrochloric acid. Meanwhile, common lab alkalis include sodium hydroxide, ammonia, and potassium hydroxide.
Around your house, alkalis pop up in oven cleaners, baking soda (great for making cakes rise!), and drain unblockers. These alkaline substances are brilliant at breaking down grease and grime, which is why they're so useful for cleaning.
Real-world Connection: Next time you're cooking or cleaning, check the labels - you'll spot acids and alkalis everywhere!
Dilution and Neutralisation Reactions
When you add water to an acid, something interesting happens - the pH gradually increases towards 7, making it less acidic. Similarly, diluting an alkali with water makes its pH drop towards 7, reducing its alkalinity.
Neutralisation is one of the most important reactions in chemistry. It happens when an acid reacts with a base, and the pH moves towards 7 (neutral). You see this in real life when people take antacids for heartburn or when farmers add lime to acidic soil.
The basic equations you need to know are: Acid + alkali → salt + water and Acid + metal oxide → salt + water. Notice how water always forms during neutralisation - that's your key clue that neutralisation has occurred.
To name salts, take the metal from the base and combine it with the acid's ending. For example, hydrochloric acid becomes 'chloride', sulfuric acid becomes 'sulfate', and nitric acid becomes 'nitrate'.
Exam Smart: Remember that neutralisation always produces water - this fact often appears in test questions!
Special Cases and Carbon Dioxide Formation
When acids react with metal carbonates, you get a bonus product alongside the usual salt and water - carbon dioxide gas! This creates a fizzing reaction that's quite dramatic to watch.
For example: hydrochloric acid + calcium carbonate → calcium chloride + water + carbon dioxide. You can test for carbon dioxide by bubbling it through lime water, which turns from clear to milky white.
Metal oxides, metal hydroxides, and metal carbonates are all types of bases that can neutralise acids. The key difference is that soluble bases dissolve in water to form alkalis, whilst insoluble ones don't affect the water's pH.
This neutralisation process is incredibly useful in everyday situations - from treating acidic soil in gardens to neutralising excess stomach acid when you've got indigestion.
Lab Tip: The lime water test for carbon dioxide is a classic experiment - the milky appearance is unmistakable!
Acid Rain and Environmental Impact
Acid rain forms when acidic gases from burning fossil fuels dissolve in water droplets in the atmosphere. The three main culprits are all non-metal oxides: sulfur dioxide, nitrogen dioxide, and carbon dioxide.
Sulfur dioxide comes from burning fossil fuels containing sulfur impurities. Nitrogen dioxide forms in car engines when spark plugs provide enough energy to make nitrogen and oxygen react (this also happens naturally during lightning storms!).
Carbon dioxide isn't just from burning fossil fuels - cement manufacturing for buildings contributes loads too. When it dissolves in oceans, it causes ocean acidification, which damages shellfish and coral reefs.
The environmental damage from acid rain includes harming plants and wildlife, eroding limestone buildings, and causing iron structures to rust faster. Understanding these reactions helps explain why reducing fossil fuel use is so important for our environment.
Environmental Connection: Every time you see weathered stone buildings or rusty metal, you're witnessing acid rain's effects firsthand!
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Acids, Bases & Neutralization
Explore the fundamentals of acids and bases, including the pH scale, neutralization reactions, and salt formation. This summary covers key concepts such as proton donors and acceptors, the role of universal indicators, and specific reactions involving metal oxides and hydroxides. Ideal for students studying chemistry.
Chemistry10
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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
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Best app on earth! no words because it’s too good
Thomas R
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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 Knowunity AI. 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 Knowunity AI. 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
Understanding Acids and Bases - National 4 Chemistry
A
Alex
@mastermind12362
Ever wonder why lemon juice tastes sour or why baking soda fizzes when it touches vinegar? It's all about acids and bases! The pH scale helps us measure how acidic or alkaline substances are, and understanding this concept explains loads... Show more
Understanding the pH Scale
The pH scale is like a measuring stick for how acidic or alkaline something is, running from 0 to 14. Think of it as a chemistry thermometer that tells you whether something will be sour (acidic) or bitter (alkaline).
Acids have a pH less than 7 - the lower the number, the more acidic it is. Alkalis (also called bases) have a pH greater than 7, and pure water sits right in the middle at exactly 7, which we call neutral.
Here's a clever trick to remember which oxides make acids or alkalis: soluble metal oxides create alkaline solutions when dissolved in water, whilst soluble non-metal oxides produce acidic solutions. If an oxide doesn't dissolve (it's insoluble), it won't change the water's pH at all.
Quick Tip: Use your data booklet to check if an oxide is from a metal or non-metal, then check its solubility - this tells you exactly what it'll do to pH!
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Acids and Alkalis in Daily Life
You encounter acids and alkalis every single day without realising it! Your fizzy drinks, fruit juices, and even the vinegar in your kitchen are all acidic substances that would score below 7 on the pH scale.
In chemistry labs, the main acids you'll work with include sulfuric acid, nitric acid, and hydrochloric acid. Meanwhile, common lab alkalis include sodium hydroxide, ammonia, and potassium hydroxide.
Around your house, alkalis pop up in oven cleaners, baking soda (great for making cakes rise!), and drain unblockers. These alkaline substances are brilliant at breaking down grease and grime, which is why they're so useful for cleaning.
Real-world Connection: Next time you're cooking or cleaning, check the labels - you'll spot acids and alkalis everywhere!
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Dilution and Neutralisation Reactions
When you add water to an acid, something interesting happens - the pH gradually increases towards 7, making it less acidic. Similarly, diluting an alkali with water makes its pH drop towards 7, reducing its alkalinity.
Neutralisation is one of the most important reactions in chemistry. It happens when an acid reacts with a base, and the pH moves towards 7 (neutral). You see this in real life when people take antacids for heartburn or when farmers add lime to acidic soil.
The basic equations you need to know are: Acid + alkali → salt + water and Acid + metal oxide → salt + water. Notice how water always forms during neutralisation - that's your key clue that neutralisation has occurred.
To name salts, take the metal from the base and combine it with the acid's ending. For example, hydrochloric acid becomes 'chloride', sulfuric acid becomes 'sulfate', and nitric acid becomes 'nitrate'.
Exam Smart: Remember that neutralisation always produces water - this fact often appears in test questions!
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Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Special Cases and Carbon Dioxide Formation
When acids react with metal carbonates, you get a bonus product alongside the usual salt and water - carbon dioxide gas! This creates a fizzing reaction that's quite dramatic to watch.
For example: hydrochloric acid + calcium carbonate → calcium chloride + water + carbon dioxide. You can test for carbon dioxide by bubbling it through lime water, which turns from clear to milky white.
Metal oxides, metal hydroxides, and metal carbonates are all types of bases that can neutralise acids. The key difference is that soluble bases dissolve in water to form alkalis, whilst insoluble ones don't affect the water's pH.
This neutralisation process is incredibly useful in everyday situations - from treating acidic soil in gardens to neutralising excess stomach acid when you've got indigestion.
Lab Tip: The lime water test for carbon dioxide is a classic experiment - the milky appearance is unmistakable!
Sign up to see the contentIt's free!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Acid Rain and Environmental Impact
Acid rain forms when acidic gases from burning fossil fuels dissolve in water droplets in the atmosphere. The three main culprits are all non-metal oxides: sulfur dioxide, nitrogen dioxide, and carbon dioxide.
Sulfur dioxide comes from burning fossil fuels containing sulfur impurities. Nitrogen dioxide forms in car engines when spark plugs provide enough energy to make nitrogen and oxygen react (this also happens naturally during lightning storms!).
Carbon dioxide isn't just from burning fossil fuels - cement manufacturing for buildings contributes loads too. When it dissolves in oceans, it causes ocean acidification, which damages shellfish and coral reefs.
The environmental damage from acid rain includes harming plants and wildlife, eroding limestone buildings, and causing iron structures to rust faster. Understanding these reactions helps explain why reducing fossil fuel use is so important for our environment.
Environmental Connection: Every time you see weathered stone buildings or rusty metal, you're witnessing acid rain's effects firsthand!
We thought you’d never ask...
What is the Knowunity AI companion?
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.
Where can I download the Knowunity app?
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Is Knowunity really free of charge?
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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 Knowunity AI. 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 Knowunity AI. 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