A salt is a compound formed when the hydrogen ions (H⁺) from an acid are replaced by a metal ion or ammonium ion from a base during neutralisation.
What are the two types of ions present in salts?
Salts consist of positively charged ions (cations) from the base and negatively charged ions (anions) from the acid.
What is a soluble salt?
A soluble salt is a salt that dissolves in water to form an aqueous solution.
Give an example of an insoluble salt.
Silver chloride (AgCl) is an example of an insoluble salt.
What type of structure do salts usually have in their solid form?
Salts have a crystalline structure due to the orderly arrangement of ions in a lattice.
What determines the shape of salt crystals?
The specific arrangement and type of ions in the salt determine its crystal shape.
What is the shape of sodium chloride crystals?
Sodium chloride (NaCl) crystals have a cubic shape.
Name a salt used in agriculture and its purpose.
Ammonium nitrate (NH₄NO₃) is used as a fertiliser to provide essential nutrients for plant growth.
Which salt is commonly used as table salt?
Sodium chloride (NaCl).
What is sodium bicarbonate (NaHCO₃) used for in the food industry?
It is used as a raising agent in baking.
Which salt is used in making plaster of Paris?
Calcium sulfate hemihydrate (CaSO₄·½H₂O).
What is potassium permanganate (KMnO₄) used for in medicine?
It is used as an antiseptic for treating wounds.
Which salt is used in the manufacture of glass and detergents?
Sodium carbonate (Na₂CO₃).
State one general solubility rule for salts.
All nitrates (NO₃⁻) are soluble in water.
Which metal ions form insoluble chlorides?
Silver (Ag⁺), lead (Pb²⁺), and mercury (Hg²⁺).
How are insoluble salts prepared?
By precipitation, which involves mixing two soluble salt solutions to form an insoluble salt.
What is crystallisation?
Crystallisation is the process of forming solid salt crystals from a solution as the solvent evaporates.
What is a flame test used for?
A flame test is used to identify metal ions in salts based on the characteristic colour they produce when heated.
What is thermal decomposition of a salt?
Thermal decomposition is when a salt breaks down into simpler substances upon heating.
Which gas is produced when carbonates react with acids?
Carbon dioxide (CO₂).
Explanation Questions
Why do salts have a crystalline structure?
Salts have a crystalline structure due to the electrostatic attraction between oppositely charged ions, which arrange themselves in a repeating lattice.
Why are most sodium and potassium salts soluble in water?
Sodium and potassium ions interact strongly with water molecules, allowing their salts to dissolve easily.
How does ammonium nitrate help in plant growth?
It provides nitrogen, an essential nutrient for plant protein synthesis and growth.
Why are nitrates always soluble in water?
Nitrate ions (NO₃⁻) do not form strong ionic bonds with cations, making them highly soluble in water.
How does crystallisation help purify salts?
During crystallisation, only the pure salt forms crystals, leaving impurities in the solution.
Why does sodium chloride have a high melting point?
The strong electrostatic forces between sodium and chloride ions require a lot of energy to break.
Why does adding silver nitrate to sodium chloride solution form a precipitate?
Silver chloride (AgCl) is insoluble in water, so it precipitates out as a solid.
How does a flame test identify metal ions?
Different metal ions emit characteristic colours when heated in a flame due to electron excitation.
Why do carbonates react with acids to produce CO₂?
The carbonate ions (CO₃²⁻) react with hydrogen ions (H⁺) to form carbonic acid, which decomposes into CO₂ and water.
Why is precipitation used to prepare insoluble salts?
Precipitation ensures the desired insoluble salt forms directly in a solution, allowing easy separation.