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Redox reactions of acids with metals

Chemical changes • Reactions of acids

Key concepts

What you'll likely be quizzed about

  • Redox refers to reactions involving the transfer of electrons between species.
  • One species undergoes oxidation by losing electrons, while another gains those electrons through reduction.
  • Charge conservation dictates that the total number of electrons lost equals the total number gained.
  • Oxidation and reduction can be identified either by changes in oxidation numbers or through half-equations demonstrating the explicit movement of electrons.
  • For example, when a metal transforms into a cation while hydrogen ions are reduced to hydrogen atoms (and then to H2), a redox reaction takes place.

Flashcards

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How does charge conservation affect writing half-equations?

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Half-equations must balance both atoms and charge; electrons are added to balance charge differences between reactants and products.

Key notes

Important points to keep in mind

Redox equals electron transfer: oxidation = loss, reduction = gain.

Metal atoms start with oxidation number 0 and increase when oxidised.

Hydrogen in acids starts at +1 and decreases to 0 when reduced to H2.

Write half-equations to show electrons explicitly and to identify oxidised/reduced species.

Balance electrons between half-equations before combining.

Spectator ions do not change oxidation state and can be omitted from ionic equations.

Metals below hydrogen in the reactivity series usually do not produce hydrogen gas with dilute acids.

Concentrated oxidising acids can have different redox pathways and may not yield H2.

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