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Acids and bases: proton transfer
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Acids give away hydrogen ions (protons). Bases accept them. Neutralisation is the transfer of a proton.
Acids and alkalis in water
Acids in aqueous solution are a source of hydrogen ions, H+.
Alkalis in aqueous solution are a source of hydroxide ions, OH−.
Alkalis neutralise acids: H+ + OH− → H2O
Alkalis in aqueous solution are a source of hydroxide ions, OH−.
Alkalis neutralise acids: H+ + OH− → H2O
Proton donors and acceptors
A hydrogen ion, H+, is just a proton.
An acid is a proton donor. A base is a proton acceptor.
Example: ammonia accepts a proton: NH3 + H+ → NH4+, so ammonia is a base.
Hydroxide ions accept protons to form water, so hydroxides are bases.
An acid is a proton donor. A base is a proton acceptor.
Example: ammonia accepts a proton: NH3 + H+ → NH4+, so ammonia is a base.
Hydroxide ions accept protons to form water, so hydroxides are bases.
Bases and alkalis
Metal oxides, metal hydroxides and ammonia can act as bases.
An alkali is a base that is soluble in water, such as sodium hydroxide, potassium hydroxide and ammonia solution.
Copper(II) oxide is a base but not an alkali, because it is insoluble.
An alkali is a base that is soluble in water, such as sodium hydroxide, potassium hydroxide and ammonia solution.
Copper(II) oxide is a base but not an alkali, because it is insoluble.
In the reaction HCl + NH3 → NH4Cl, which substance is the acid and which is the base?
- HCl gives a proton (H+) to NH3.
- NH3 accepts the proton, forming NH4+.
Answer: HCl is the acid (proton donor); NH3 is the base (proton acceptor).
Acids are sources of H+ ions and are proton donors. Bases are proton acceptors: metal oxides, metal hydroxides and ammonia. Alkalis are soluble bases, sources of OH− ions. Neutralisation: H+ + OH− → H2O.
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