Acids with Reactive Metals (DP IB Chemistry) : Revision Note

Acids with Reactive Metals

Metals and acids

• The typical reaction of a metal and an acid can be summarised as

acid + metal  →  salt + hydrogen

• For example:

2HCl (aq)  +  Zn (s)  → ZnCl₂ (aq) + H₂ (g)

hydrochloric acid + zinc  →  zinc chloride* + hydrogen

H₂SO₄ (aq) + Fe (s) → FeSO₄ (aq) + H₂ (g)

sulfuric acid + iron → iron(II) sulfate* + hydrogen

*zinc chloride and iron(II) sulfate are salts

• A salt is an ionic compound formed when the hydrogen of an acid is replaced by a metal or another positive ion

• Clearly, the extent of the reaction depends on the reactivity of the metal and the strength of the acid

• Very reactive metals would react dangerously with acids and these reactions are not usually carried out

• Metals low in reactivity do not react at all

  • For instance, copper does not react with dilute acids

• Stronger acids will react more vigorously with metals than weak acids

• What signs of reaction would be expected to be different between the two?

  • Faster reaction seen as:

    • more effervescence

    • the metal dissolves faster

Ionic Equations

• The reactions of acids and metals can be written as ionic equations showing only the species that has changed in the reaction

• Zinc reacts with hydrochloric acid to give a salt and hydrogen

  • Zinc metal is being oxidised to a zin ion as shown in the table

Table to show the relative reducing power of metals

Mg	Strongest reducing agents – lose electrons most easily (readily oxidised)
Al
Zn
Fe
Pb
H
Cu
Ag	Weakest reducing agents – lose electrons least easily (not readily oxidised)