Reactions of Acids (Edexcel GCSE Chemistry: Combined Science)

Reactions of acids with metals

• Only metals above hydrogen in the reactivity series will react with dilute acids
• The more reactive the metal then the more vigorous the reaction will be
• Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids
• When acids react with metals they form a salt and hydrogen gas:
• The general equation is:

metal + acid ⟶ salt + hydrogen

• Some examples of metal-acid reactions and their equations are given below:

Acid-Metals Reactions Table

• In general, we can summarise the reaction of a metal that forms a +2 ion as follows:

Acids-Metals Summary Table

Reaction of acids with oxides & hydroxides

• When an acid reacts with an oxide or hydroxide, a neutralisation reaction occurs
• Metal oxides and metal hydroxides act as bases
• In all acid-base neutralisation reactions, a salt and water are produced:

acid + base ⟶ salt + water

• The identity of the salt produced depends on the acid used and the positive ions in the base
• Hydrochloric acid produces chlorides, sulfuric acid produces sulfate salts and nitric acid produces nitrates
• The following are some specific examples of reactions  between acids and metal oxides / hydroxides:

2HCl + CuO ⟶ CuCl₂ + H₂O

H₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O

HNO₃ + KOH ⟶ KNO₃ + H₂O

• In general, we can summarise the reaction of metals and bases as follows:

Acids and Metals Oxides or Hydroxides Summary Table

Reactions of Acids with Metal Carbonates

• Acids will react with metal carbonates to form the corresponding metal salt, carbon dioxide and water
• These reactions are easily distinguishable from acid – metal oxide/hydroxide reactions due to the presence of effervescence caused by the carbon dioxide gas

Acids & Metal Carbonates Reactions Table

• The following are some specific examples of reactions  between acids and metal carbonates:

2HCl + Na₂CO₃ ⟶ 2NaCl + H₂O + CO₂

H₂SO₄ + CaCO₃⟶ CaSO₄ + H₂O + CO₂

Neutralisation

• The chemistry of neutralisation reactions can be explained using ionic equations
• Ionic equations are used to show only the particles that chemically participate in a reaction
• The other ions present are not involved and are called spectator ions
• For example the neutralisation reaction between hydrochloric acid and sodium hydroxide:

HCl + NaOH ⟶ NaCl + H₂O

• If we write out all of the ions present in the equation we get:

H⁺  +  Cl^- + Na⁺  +  OH^- ⟶ Na⁺  +  Cl^- + H₂O

• The spectator ions are thus Na⁺ and Cl^–.
• Removing these from the previous equation leaves the overall net ionic equation:

H⁺  +  OH^- ⟶ H₂O

• The H⁺ ions come from the acid and the OH^– ions come from the base, both combine to form the product water molecules
• This ionic equation is the same for all acid-base neutralisation

Hazards

Hazard symbols you may see in relation to acids

• The hazards associated with acids depend on the type and concentration of the acid
• Most dilute acids either require no hazard symbol or they are an irritant, so require the symbol to show they are harmful to health
  • Eye protection should be worn when handling
• Moderately concentrated acids are often corrosive
  • In addition to eye protection, gloves should also be worn
• Some concentrated acids, e.g. nitric acid, are oxidising which can cause or intensify a fire in contact with combustible materials
  • Eye protection and gloves are necessary when handling concentrated acids and the use of a fume cupboard is often required