States of matter
Read our general notes on Risk Assessment
What does it mean when there is BOTH a chemical change and a physical change in a reaction?
At advanced level the distinction between physical and chemical changes is not useful. In an elementary course, dissolving is regarded as a physical change but you will learn in an advanced course that dissolving involves chemical bonding between solvent and solute molecules so it is certainly a chemical change on a molecular scale. The dissolved atoms, molecules or ions are at least chemically combined in some way with solute molecules and they may well be more radically changed. Hydrogen chloride molecules, for example, ionise when they dissolve in water.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 14 December 2006
