GCSE Chemistry revision

State symbols

How bonding and structure are related to the properties of substances

AQA 4.2.2.2 Foundation & Higher

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State symbols are shorthand notations added in brackets after a chemical formula to show which physical state a substance is in during a reaction.
The four state symbols are: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous (dissolved in water).
A substance is described as aqueous (aq) when it is an ionic compound dissolved in water, meaning it is neither a pure solid nor a pure liquid.

1. What Are State Symbols? AQA

State symbols are shorthand notations added in brackets after a chemical formula to show which physical state a substance is in during a reaction.
The four state symbols are: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous (dissolved in water).
A substance is described as aqueous (aq) when it is an ionic compound dissolved in water, meaning it is neither a pure solid nor a pure liquid.

In the reaction of sodium with water, sodium is written as Na_(s) because it is a solid metal at room temperature.
Water is written as H₂O_(l) because it is a liquid at room temperature.
Sodium hydroxide is written as NaOH_(aq) because it dissolves into the water, making it an aqueous solution.
Hydrogen gas is released during the reaction and is written as H₂_(g).

2. State Symbols in Action: Sodium and Water AQA

In the reaction of sodium with water, sodium is written as Na_(s) because it is a solid metal at room temperature.
Water is written as H₂O_(l) because it is a liquid at room temperature.
Sodium hydroxide is written as NaOH_(aq) because it dissolves into the water, making it an aqueous solution.
Hydrogen gas is released during the reaction and is written as H₂_(g).

The melting point is the temperature at which a substance changes from solid to liquid, and the boiling point is the temperature at which it changes from liquid to gas.
Below the melting point, a substance is a solid; between the melting and boiling points, it is a liquid; above the boiling point, it is a gas.
Using a number line to plot melting and boiling points is a helpful way to visualise which state a substance is in at any given temperature.

3. Melting Points and Boiling Points AQA

The melting point is the temperature at which a substance changes from solid to liquid, and the boiling point is the temperature at which it changes from liquid to gas.
Below the melting point, a substance is a solid; between the melting and boiling points, it is a liquid; above the boiling point, it is a gas.
Using a number line to plot melting and boiling points is a helpful way to visualise which state a substance is in at any given temperature.

At 800°C, water (melting point 0°C, boiling point 100°C) is a gas because 800°C is well above its boiling point.
At 800°C, copper (melting point 1083°C) is a solid because 800°C has not yet reached its melting point.
At 800°C, magnesium (melting point 650°C, boiling point 1107°C) is a liquid because 800°C falls between its melting and boiling points.
In GCSE exams, you may be given a data table of melting and boiling points and asked to predict the state of a substance at a specified temperature.

4. Predicting States at a Given Temperature AQA

At 800°C, water (melting point 0°C, boiling point 100°C) is a gas because 800°C is well above its boiling point.
At 800°C, copper (melting point 1083°C) is a solid because 800°C has not yet reached its melting point.
At 800°C, magnesium (melting point 650°C, boiling point 1107°C) is a liquid because 800°C falls between its melting and boiling points.
In GCSE exams, you may be given a data table of melting and boiling points and asked to predict the state of a substance at a specified temperature.