8.1.3 Characteristic Reactions of Acids

Metals and acids

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

acid + metal  →  salt + hydrogen

• For example:

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

hydrochloric acid + zinc    →  zinc chloride + hydrogen

• Clearly, the extent of 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

  • More exothermic

Metals and oxides

• The reaction of an acid with a metal oxide forms two products:

acid + metal oxide →  salt + water

• For example:

2HCl (aq)  +      CaO (s)     →        CaCl₂ (aq)      +    H₂O (l)

  hydrochloric acid + calcium oxide →  calcium chloride + water

Metals and hydroxides

• The reaction with a metal hydroxide and an acid follows the same pattern as an oxide:

acid + metal hydroxide →  salt + water

• A suitable example might be:

 H₂SO₄ (aq) +  Mg(OH)₂ (s)  →     MgSO₄ (aq)  +    2H₂O (l)

 sulfuric acid  + magnesium hydroxide →  magnesium sulfate + water

Metals and carbonates

• The reaction between a metal carbonate and an acid produces three products:

acid + metal carbonate → salt + water + carbon dioxide

• For example:

    2HNO₃ (aq) + CuCO₃ (s)   →    Cu(NO₃)₂ (aq) + H₂O (l) + CO₂ (g)

nitric acid + copper carbonate → copper nitrate + water + carbon dioxide

Metals and hydrogencarbonates

• The reaction between a metal hydrogencarbonate and an acid is the same as the carbonate reaction with a slight difference in stoichiometry:

acid + metal hydrogencarbonate → salt + water + carbon dioxide

• An example of this would be:

HCl (aq)   +     NaHCO₃ (s)     →    NaCl (aq) + H₂O (l) + CO₂ (g)

• The acids and bases needed to make different salts can be deduced using the principles covered in the previous section
• The table below summarises these reactions

Making Salts Table

• Note that although some metals can be used to make salts, they are not classified as bases as water is not a product of the reaction

Answer:

The correct option is D.

• • Metal oxides when reacting with acids produce a salt and water as the only products