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Acids and bases flash cards

Flash cards on acids, bases and alkalis: the pH scale, indicators, neutralisation, the reactions of acids, naming salts, strong and weak acids, gas tests and titration.

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The cards, front and back

1
Front
What is an acid?
Back
A substance that releases hydrogen ions (H⁺) when it dissolves in water. In a wider definition, an acid is a proton donor.
2
Front
What is a base, and what is an alkali?
Back
A base is a substance that neutralises an acid to form a salt and water, such as a metal oxide or hydroxide. An alkali is a base that dissolves in water, releasing hydroxide ions (OH⁻).
3
Front
What does the pH scale measure?
Back
How acidic or alkaline a solution is, usually on a scale from 0 to 14. pH 7 is neutral, below 7 is acidic and above 7 is alkaline.
4
Front
How much does the hydrogen ion concentration change for each pH unit?
Back
By a factor of ten. A solution at pH 3 has ten times the concentration of H⁺ ions of a solution at pH 4.
5
Front
What colour is litmus in an acid and in an alkali?
Back
Red in an acid and blue in an alkali.
6
Front
What is universal indicator?
Back
A mixture of indicators that changes through a range of colours to show the approximate pH: red for strong acids, green at neutral, and blue to purple for strong alkalis.
7
Front
What colour are phenolphthalein and methyl orange in acid and alkali?
Back
Phenolphthalein is colourless in acid and pink in alkali. Methyl orange is red in acid and yellow in alkali.
8
Front
What is neutralisation?
Back
The reaction between an acid and a base that produces a salt and water. The ionic equation is H⁺ + OH⁻ → H₂O.
9
Front
Acid + metal → ?
Back
A salt and hydrogen. For example, magnesium + hydrochloric acid → magnesium chloride + hydrogen.
10
Front
Acid + metal oxide or metal hydroxide → ?
Back
A salt and water. For example, copper oxide + sulfuric acid → copper sulfate + water.
11
Front
Acid + metal carbonate → ?
Back
A salt, water and carbon dioxide. For example, calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide.
12
Front
Which salts do hydrochloric, sulfuric and nitric acids make?
Back
Hydrochloric acid makes chlorides, sulfuric acid makes sulfates and nitric acid makes nitrates.
13
Front
How do you test for hydrogen gas?
Back
Hold a lit splint at the mouth of the test tube. Hydrogen burns with a squeaky pop.
14
Front
How do you test for carbon dioxide?
Back
Bubble the gas through limewater (calcium hydroxide solution). Carbon dioxide turns it milky or cloudy.
15
Front
What is the difference between a strong acid and a weak acid?
Back
A strong acid fully ionises in water, such as hydrochloric acid. A weak acid only partly ionises, such as ethanoic acid.
16
Front
What is the difference between strong and concentrated?
Back
Strong or weak describes how fully the acid ionises. Concentrated or dilute describes how much acid is dissolved in a given volume of water.
17
Front
Name two common weak acids and where they are found.
Back
Ethanoic (acetic) acid in vinegar and citric acid in citrus fruits such as lemons.
18
Front
Name a common weak alkali.
Back
Ammonia solution, which is used in some household cleaners.
19
Front
What is a titration used for?
Back
To find the exact volume of one solution needed to react completely with a known volume of another, using an indicator to show the end point. It lets you work out an unknown concentration.
20
Front
How do you make a pure, dry sample of a soluble salt from an insoluble base?
Back
Add the base to warm acid until no more dissolves, filter off the excess, heat the solution to evaporate some water, then leave it to crystallise and dry the crystals.
21
Front
Give an everyday use of neutralisation.
Back
Farmers add lime (calcium oxide or hydroxide) to neutralise acidic soil, and antacid tablets neutralise excess stomach acid.

How to use this template

This deck covers acids, bases and alkalis for school chemistry: definitions, the pH scale and what each pH unit means, the colours of common indicators, neutralisation and its ionic equation, the reactions of acids with metals, oxides, hydroxides and carbonates, naming salts, strong and weak acids, gas tests, titration and making a soluble salt. It suits GCSE and IGCSE chemistry, Year 9 to Year 11 science, high school chemistry and a quick revision for AP or IB chemistry before the deeper work on pH calculations. Learn the general equations first, then the examples, using Learn mode, then Test mode with spaced repetition. Print it double-sided for a quick class quiz.

Tips

Learn the three general equations for acids as patterns, then practise writing word equations for new examples.
Name salts in two parts: the metal from the base or metal, then the ending from the acid (chloride, sulfate or nitrate).
Keep a small table of indicator colours and redraw it from memory until it is correct.
Use the words strong and concentrated carefully. Exams often test whether you know the difference.
For practical questions, describe each step with its purpose, such as filtering to remove excess solid.

Make it fit

Add pH calculations, buffers or Brønsted–Lowry pairs for higher-level courses.
Add the method and results table from a titration your class did.
Make reverse cards: put the products on the front and ask which reactants made them.
Split the deck into a definitions and indicators set and a reactions and salts set.

Updated October 28, 2026

The cards, front and back

How to use this template

Tips

Make it fit

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