Overview
This lecture covers neutralization reactions between acids and different types of bases: metal oxides, metal hydroxides, and metal carbonates. It also explains how to prepare soluble salts using insoluble bases, with step-by-step instructions for the process.
Reactions with Metal Oxides and Hydroxides
- When acids react with metal oxides or metal hydroxides, the products are always a salt and water.
- Example: Hydrochloric acid reacts with sodium oxide (a metal oxide) to form sodium chloride (salt) and water. The sodium ions (Na⁺) from the base combine with the chloride ions (Cl⁻) from the acid.
- Example: Sulfuric acid reacts with potassium hydroxide (a metal hydroxide) to produce potassium sulfate (K₂SO₄, the salt) and water. Two potassium ions (K⁺) combine with one sulfate ion (SO₄²⁻).
- The general pattern: the positive ion from the base combines with the negative ion from the acid to form the salt, and water is always produced.
- It is important to write the correct formula for the salt by matching the charges of the ions and to balance the chemical equation.
Reactions with Metal Carbonates
- Acids reacting with metal carbonates produce a salt, water, and carbon dioxide gas.
- Example: Nitric acid reacts with calcium carbonate to form calcium nitrate (the salt), water, and carbon dioxide. The calcium ion (Ca²⁺) from the carbonate combines with two nitrate ions (NO₃⁻) from the acid to form Ca(NO₃)₂.
- As with other reactions, ensure the charges are balanced when writing the salt formula, and balance the overall equation.
- The release of carbon dioxide gas is a distinguishing feature of these reactions.
Making Soluble Salts Using Insoluble Bases
- To prepare a soluble salt, react an acid with an insoluble base such as a metal oxide, hydroxide, or carbonate.
- Steps for the process:
- Place some dilute acid (e.g., hydrochloric acid) in a beaker and gently heat it using a Bunsen burner.
- Gradually add the insoluble base (e.g., copper oxide) in small amounts. The base will react and disappear as it forms the soluble salt and water.
- Continue adding the base until it no longer dissolves, indicating that all the acid has been neutralized and the base is now in excess.
- Filter the mixture using filter paper and a funnel to remove the excess, unreacted base. The filtrate contains the dissolved soluble salt (e.g., copper chloride).
- To obtain solid salt crystals, gently heat the filtered solution using a water bath or electric heater (not a Bunsen burner) to evaporate some of the water. Avoid overheating to prevent damaging the salt.
- Once crystals begin to form, stop heating and allow the solution to cool, which will produce more crystals.
- Filter out the crystals and dry them by dabbing with filter paper or leaving them in a warm place.
- This method allows you to make pure crystals of a soluble salt from an insoluble base and an acid.
Key Terms & Definitions
- Neutralization reaction: A chemical reaction where an acid and a base react to form a salt and water.
- Salt: An ionic compound formed from the positive ion of a base and the negative ion of an acid.
- Insoluble base: A base that does not dissolve in water, such as metal oxides, hydroxides, or carbonates.
- Soluble salt: A salt that dissolves in water to form an aqueous solution.
- Excess: The condition where more of a substance is present than can react, ensuring all of the other reactant is used up.
Action Items / Next Steps
- Practice writing and balancing chemical equations for reactions between acids and metal oxides, hydroxides, and carbonates.
- Review and memorize the steps for preparing soluble salts using insoluble bases.
- Ensure you can identify the correct ions to form the salt and balance the charges and equations.
- Familiarize yourself with the process of filtering, evaporating, and crystallizing salts from solution.