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Chemistry110 views·Updated Jun 9, 2026·2 pagesUnderstanding Acids and Bases: Chemistry Revision Guide
Emilie@emi_cxxc
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Understanding Acids, Bases and the pH Scale
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.
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Neutralisation Reactions
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.
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Chemistry110 views·Updated Jun 9, 2026·2 pagesUnderstanding Acids and Bases: Chemistry Revision Guide
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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Understanding Acids, Bases and the pH Scale
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.
2
of 2Sign up to see the content. It's free!
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Neutralisation Reactions
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.
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Similar content
Most popular content: Acid-base Chemistry
9Most popular content in Chemistry
9Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google 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 SiOS 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 KlichAndroid 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.
AnnaiOS user