GCSE chemistry: reactions, bonding and lab tests
These pages cover seven topics from GCSE chemistry, with links back to KS3 where it applies. You can look up the reactivity series and the pH scale, balance an equation, draw a dot and cross diagram, check a flame colour or gas test, and work out an Rf value. Each page gives the answer first and then shows how AQA, Edexcel and OCR word it.
Chemistry hub
- Reactivity series: the order of metals for each exam board
- The pH scale: acids, alkalis and neutral solutions
- Flame test colours for the five metal ions
- Balancing equations: how to balance a chemical equation
- Ionic bonding and dot and cross diagrams
- Tests for gases: hydrogen, oxygen, carbon dioxide and chlorine
- Chromatography Rf value: how to calculate it
How the topics fit together
Several of these topics start with atoms and their electrons. When a metal meets a non-metal, electrons move from one atom to the other and ions form. That is ionic bonding. Some metals form positive ions more easily than others, so they react faster with water or acids. Ranking them gives the reactivity series.
Every reaction keeps the same atoms, just rearranged. A balanced equation shows this in symbols. Once you can write one, you can describe what happens when an acid meets a metal, or when an acid meets an alkali.
The last group of pages is about finding out what a substance is. A chemist can test a gas, hold a sample in a flame or run it up a strip of paper.
Metals, acids and alkalis
The reactivity series page puts each board's list of metals side by side. AQA names eight metals. Edexcel names ten metals plus carbon and hydrogen, and OCR Twenty First Century names ten metals plus hydrogen. OCR Gateway gives no fixed list at all.
The pH scale page has a scale from 0 to 14 that you can tap. It explains why each step down means ten times as many hydrogen ions, and how neutralisation makes a salt and water.
Bonding and equations
On the ionic bonding page you can build a dot and cross diagram and move electrons from a metal atom to a non-metal atom. It shows how the group number of an element gives the charge on its ion.
The page on balancing equations has a balancer. You type a number in front of each formula, and it counts the atoms on each side for you. Three worked examples take you through the method one line at a time.
Chemical tests and analysis
The page on tests for gases covers hydrogen, oxygen, carbon dioxide and chlorine. For each gas it gives the test and the result you should see.
Flame test colours lists the five metal ions with each board's colour word. AQA and Edexcel use different words for lithium and copper, and the page shows both. The chromatography page has an Rf calculator with three worked examples, including one where the units do not match.
Which specifications these pages follow
We checked each fact against the current specification from its board. That covers six GCSE courses and the KS3 programme:
- AQA GCSE Chemistry (8462) and Combined Science: Trilogy (8464)
- Edexcel GCSE Chemistry (1CH0) and Combined Science (1SC0)
- OCR Chemistry A, Gateway Science (J248)
- OCR Chemistry B, Twenty First Century Science (J258)
- The KS3 National Curriculum for science in England
Where the boards say different things, the pages name each board. The metal lists and the flame colour words are the clearest cases. Only AQA prints the Rf formula as a formula. OCR Gateway expects you to recall it, and every board asks you to use it.
Higher tier and separate chemistry
Some ideas only come up at Higher tier, and the pages flag them. On AQA, Edexcel and OCR Gateway, ionic equations are Higher tier. For AQA, strong and weak acids and the ten times rule for pH are Higher tier too.
Flame tests are for separate chemistry students only. AQA 8464 and Edexcel 1SC0 leave them out, and both OCR courses mark them as separate science. On AQA and Edexcel, the gas tests and Rf values appear in Combined Science as well.
KS3 covers the pH scale, acids and alkalis, the order of metals and carbon, and chromatography as a way to separate mixtures. Ionic bonding, flame colours and Rf values begin at GCSE.
Common mistakes
- Learning one board's list or colour word and using it in another board's exam.
- Treating a strong acid and a concentrated acid as the same. Strength is about splitting into ions.
- Balancing an equation by changing the small numbers inside a formula.
Start with Balance It, then try the game linked at the foot of each topic page.
Questions people ask
Which board am I on?
Ask your teacher. Each course has a code, such as 8462 for AQA GCSE Chemistry or J258 for OCR Twenty First Century, and the list above gives all six.
Do these pages work for Combined Science?
For AQA and Edexcel, yes, apart from flame tests. Their Combined Science courses include the reactivity series, pH, bonding, equations, gas tests and Rf values. Flame tests belong to GCSE Chemistry only.
Do I need to sign up or pay?
No. You can read every page and play every game on this site for free, and there is no account to make.