GCSE · Chemistry · AQA · Spec 8462

State symbols

Copper sulfate solution looks like a liquid. You could pour it. So why would a chemist never label it (l)?

Sort it first

Which badge does each substance wear?

In an equation, every formula wears a small bracketed badge saying what state it is in. Pick a substance, then put it under the badge you think it wears. Guess if you have to — the reason appears as soon as you commit.

Still to sort

(s) solid (0)

The substance is a solid.

Where the line is: (s) means solid — it does not stand for 'solution'. A solution gets (aq).

(l) liquid (0)

The substance itself is a liquid.

Where the line is: A solution is runny, but it is not (l). (l) is for a substance that is itself a liquid.

(g) gas (0)

The substance is a gas.

(aq) aqueous (0)

The substance is dissolved in water — an aqueous solution.

Where the line is: (s), (l) and (g) are the three states of matter. (aq) is the extra one: it tells you the substance is dissolved in water.

9 of 9 still to sort.

Most of these come from two real equations — you will meet both of them properly in a moment.

Watch out: (aq) and (l) are the pair that catch people out. Dissolved in water gets (aq). A substance that is itself a liquid gets (l).

Where the badges go

Anatomy of an equation with state symbols

Showing 2 layers: Formulae, State symbols

Layers

Explore

tap a part ↓

Now each formula wears its state symbol, straight after it: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s).

Switch the state symbols off and on, then tap each part to see what it is doing.

The trap

What does (aq) really mean?

Copper sulfate solution is written CuSO₄(aq). Water formed in a reaction is usually written H₂O(l). You could pour either of them — so why do they get different badges?

Which idea is closest to what you think right now?

(aq) just means it's a liquid.(aq) means the substance is water.(aq) means the substance is dissolved in water.(aq) and (l) mean the same thing, so either will do.

How sure are you?

I'm sureI think soI'm guessing

(aq) just means it's a liquid.

This is a common misconception

Tempting — a solution is runny. But liquid already has its own symbol, (l). (aq) says something more specific: the substance is dissolved in water. Copper sulfate solution is copper sulfate dissolved in water, so it is (aq).

(aq) means the substance is water.

This is a common misconception

Close — water is involved — but it's the other way round. The water is what the substance is dissolved in. Water itself, formed in a reaction, is usually labelled (l), because in its standard state water is a liquid.

(aq) means the substance is dissolved in water.

This matches the evidence

Exactly. (aq) marks an aqueous solution: the substance is there dissolved in water. That's why an acid, normally used as a solution in water, takes (aq) and not (l).

(aq) and (l) mean the same thing, so either will do.

This is a common misconception

They don't. (l) says the substance itself is a liquid; (aq) says it is dissolved in water. Swap them and your equation describes the wrong state.

Dissolved in water → (aq). The substance itself a liquid → (l). Water formed in a reaction → usually (l).

Your turn to write it

Add the state symbols

Calcium carbonate decomposes into calcium oxide and carbon dioxide. Add the state symbols to the equation.

CaCO₃ → CaO + CO₂The symbol equation with no state symbols yet. You sorted all three of these substances at the top of the page.
missing step

Which line is step 2?

(s)CaCO₃CaCO₃(s)CaCO₃(aq)

Spot the slip

Where does this answer go wrong?

Add state symbols to the equation for iron reacting with copper sulfate solution: Fe + CuSO₄ → FeSO₄ + Cu

A student's answer — which line goes wrong?

Iron is a solid, so: Fe(s)
Copper sulfate solution is a runny liquid, so: CuSO₄(l)
Iron sulfate ends up in the same solution, so it gets the same symbol: FeSO₄(l)
Copper is formed as a solid, so: Cu(s)
Final answer: Fe(s) + CuSO₄(l) → FeSO₄(l) + Cu(s)

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The tiny bracketed badges that tell you whether each substance in an equation is a solid, a liquid, a gas — or dissolved in water.

What you need to know

A state symbol is a short bracketed label showing the physical state of each reactant and each product in a chemical equation.
There are four: (s) solid, (l) liquid, (g) gas and (aq) aqueous solution — dissolved in water.
Each state symbol goes straight after the formula of the substance it describes.
State symbols are written as part of symbol equations — the equations that use chemical formulae.

The big picture

A state symbol is a short bracketed label showing the physical state of each reactant and each product in a chemical equation: (s) solid, (l) liquid, (g) gas and (aq) for an aqueous solution — dissolved in water. Each one goes straight after its formula in a symbol equation, as in CaCO₃(s) → CaO(s) + CO₂(g). The hard part is telling (aq) from (l). Copper sulfate solution is (aq), and so is an acid, which is normally used as a solution in water. Water formed in a reaction is usually (l).

Key points

1(s), (l) and (g) are the three states of matter. (aq) is different: it tells you the substance is dissolved in water.

2Acids are normally used as solutions in water, so an acid takes (aq), not (l).

3Water formed in a reaction is usually labelled (l), because in its standard state water is a liquid.

4Two equations to know by heart: CaCO₃(s) → CaO(s) + CO₂(g) and Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s).

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Worked example

Problem

An imaginary reaction (the letters stand in for real formulae): solid A is added to a solution of B in water. They react to form C, which stays dissolved in the water, and D, which is given off as a gas. Write A + B → C + D with state symbols.

⚠ Watch out

Writing (l) for a solution. Copper sulfate solution is runny, but the copper sulfate is dissolved in water, so it is CuSO₄(aq), not CuSO₄(l). Keep (l) for a substance that is itself a liquid — such as water formed in a reaction, which is usually (l).

🧠

Memory hook

Dissolved IN water? (aq). IS the water? (l). Runny is not the test.

✓

Check yourself

Cover the page. Write the four state symbols and what each means. Then explain why an acid used in a reaction is normally (aq), but water formed in a reaction is usually (l).

Flashcards

(12)

What is a state symbol?

A short bracketed label showing which physical state a reactant or product is in, in a chemical equation.

What does (s) stand for?

Solid. (It does not stand for 'solution'.)

What does (l) stand for?

Liquid — the substance itself is a liquid.

What does (g) stand for?

Gas.

What does (aq) stand for?

An aqueous solution: the substance is dissolved in water.

Where does a state symbol go in an equation?

Straight after the formula of the substance it describes.

Which kind of equation carries state symbols?

Symbol equations — the equations written with chemical formulae.

Which state symbol does an acid normally take, and why?

(aq), because acids are normally used as solutions in water.

Which state symbol does water formed in a reaction usually take, and why?

(l), because in its standard state water is a liquid.

Write the decomposition of calcium carbonate with state symbols.

CaCO₃(s) → CaO(s) + CO₂(g)

In Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s), which substances are (aq), and why?

Copper sulfate and iron sulfate — they are the two compounds in solution in water.

What is the difference between (l) and (aq)?

(l): the substance itself is a liquid. (aq): the substance is dissolved in water.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Which badge does each substance wear?

What does (aq) really mean?

Add the state symbols

Where does this answer go wrong?

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