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This subtopic covers the following learning objectives from the Cambridge IGCSE Chemistry 0620 syllabus:
Core: Name appropriate apparatus for the measurement of time, temperature, mass and volume, including:
Core: Suggest advantages and disadvantages of experimental methods and apparatus
Core: Describe a:
A solution is formed when a substance (solute) dissolves into another substance (solvent). Solutions are a type of mixture composed of two or more substances that are completely mixed to become one single phase.
When solid salt dissolves in liquid water, it produces a salt solution. The solid completely disappears into the liquid, forming a uniform mixture.
Solute: The solid substance that has dissolved in a liquid (the solvent) to form a solution. In a salt solution, the salt is the solute.
Solvent: The liquid that dissolves the solid solute to form a solution. Water is the most common solvent, but other liquids can also act as solvents. Liquids in organic chemistry that can act as solvents are called organic solvents (such as ethanol, propanone, and trichloroethane).
Solution: The mixture of one or more solutes dissolved in a solvent. For example, seawater is a solution of various salts dissolved in water.
🔑 Key Concept: In a solution, the solute particles are completely and uniformly dispersed among the solvent particles and cannot be seen individually.
The chemical world is very complex, owing to the vast range of pure substances available and the variety of ways in which these substances can mix with each other. Each mixture must be made from at least two parts, which may be solid, liquid, or gas.
Mixture: Two or more substances mixed together but not chemically combined – the substances can be separated by physical means.
In some mixtures, the states are completely mixed to become one single phase (solutions). In other types of mixture, the states remain separate, such as:
Suspension: A mixture containing small particles of an insoluble solid, or droplets of an insoluble liquid, spread (suspended) throughout a liquid. Suspensions often form after a precipitation reaction.
Soluble: A solute that dissolves in a particular solvent. For example, salt is soluble in water.
Insoluble: A substance that does not dissolve in a particular solvent. For example, sand is insoluble in water.
Miscible: If two liquids form a completely uniform mixture when added together, they are said to be miscible. Alcohol and water are completely miscible – alcohol mixes (dissolves) completely with water.
📌 Important: Water is the commonest solvent in use. Two-thirds of the Earth's surface is covered by a solution of various salts in water. Dissolved gases like oxygen and carbon dioxide are also present in seawater and are important for life to exist in the oceans.
While we most often think of a solution as being made of a solid dissolved in a liquid, solutions can exist in other forms:
Alloys: Mixtures of elements (usually metals) designed to have properties useful for a particular purpose, such as solder (an alloy of tin and lead) which has a low melting point.
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