Neutralisation (OCR Gateway GCSE Chemistry)

• Metal oxides and metal hydroxides act as bases
• Bases have pH values above 7
• Many bases are insoluble in water but the ones that do dissolve in water are called alkalis
• Examples of alkalis are soluble metal hydroxides such as NaOH and Ca(OH)₂
• When bases react with acids, a neutralisation reaction occurs
• In all acid-base neutralisation reactions, salt and water are produced:

acid + base ⟶ salt + water

• This neutralisation reaction can be generalised to the H⁺ ions (from the acid) reacting with the OH^– ions (from the base) to produce water
• The overall ionic equation for this is: 

H⁺ + OH^– ⟶ H₂O

• 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

Acids and Metals Oxides or Hydroxides Summary Table

• 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

Acids & 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:

acid + base ⟶ salt + water + carbon dioxide

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

Acids & 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

Acid-Metal Reactions Table

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

• The name of a salt has two parts
• The first part comes from the metal, metal oxide, metal hydroxide or metal carbonate used in the reaction
• The second part comes from the acid
• The name of the salt can be determined by looking at the reactants
• For example hydrochloric acid always produces salts that end in chloride and contain the chloride ion, Cl^–
• Other examples:
  • Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride
  • Zinc oxide reacts with sulfuric acid to produce zinc sulfate
• You need to be able to predict all the products based on the reactants used, not just the salt
• For example:

magnesium carbonate + nitric acid        ⟶     magnesium nitrate + carbon dioxide + water 

copper oxide + sulfuric acid          ⟶       copper sulfate + water 

sodium + hydrochloric acid     ⟶    sodium chloride + hydrogen

Answer:

1. 1. Calcium chloride, water and carbon dioxide 
   2. Sodium sulfate and water 
   3. Magnesium nitrate and hydrogen

Answer: 

• • Zinc and sulfuric acid react to produce the salt, zinc sulfate and hydrogen gas 
  • The balanced equation is therefore: Zn  +   H₂SO₄     ⟶    ZnSO₄   +     H₂