State any two uses of sodium, magnesium, copper, zinc, aluminium, iron, gold, and silver. Distinguish between hard and soft water and state 3 advantages of each.

Here are the answers to your questions.

4. State any two uses of the following metals.

• i. Sodium:
  • Used in street lamps (sodium vapor lamps).
  • Used as a coolant in nuclear reactors.
• ii. Magnesium:
  • Used in flares and fireworks.
  • Used in lightweight alloys for aircraft.
• iii. Copper:
  • Used in electrical wiring.
  • Used in plumbing pipes.
• iv. Zinc:
  • Used for galvanizing steel to prevent rust.
  • Used in batteries (e.g., dry cells).
• v. Aluminium:
  • Used in aircraft construction.
  • Used for making beverage cans.
• vi. Iron:
  • Used in construction (e.g., steel beams).
  • Used for making tools and machinery.
• vii. Gold:
  • Used in jewelry.
  • Used in dentistry and electronics.
• viii. Silver:
  • Used in jewelry and coinage.
  • Used in photography and electrical contacts.

5. (a) Distinguish between hard and soft water.

• Hard water contains dissolved mineral ions, primarily calcium ($\text{Ca}^{2+}$) and magnesium ($\text{Mg}^{2+}$) ions, and does not readily form lather with soap.
• Soft water contains very few or no dissolved mineral ions and readily forms lather with soap.

5. (b) State 3 advantages of soft water and 3 advantages of hard water.

• Advantages of soft water:
  • Forms lather easily with soap, reducing soap consumption.
  • Does not form scale in pipes and boilers, preventing blockages.
  • Better for washing clothes and dishes as it cleans more effectively.
• Advantages of hard water:
  • Contains essential minerals like calcium and magnesium, beneficial for human health.
  • Has a pleasant taste due to dissolved minerals.
  • Suitable for brewing beer and tanning leather.

5. (c) State 2 disadvantages of soft water and 2 disadvantages of hard water.

• Disadvantages of soft water:
  • Lacks beneficial minerals like calcium and magnesium.
  • Can be corrosive to lead pipes, dissolving lead into the water.
• Disadvantages of hard water:
  • Wastes soap as it does not readily form lather.
  • Forms scale (limescale) in kettles, pipes, and boilers, reducing efficiency.

5. (d) Explain any 3 ways of removing water hardness.

• 1. Boiling: This method removes temporary hardness. Boiling causes the soluble bicarbonates of calcium and magnesium to decompose into insoluble carbonates, which then precipitate out. $$\text{Ca(HCO}_3)_2\text{(aq)} \xrightarrow{\text{heat}} \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$$
• 2. Adding washing soda (sodium carbonate): Washing soda reacts with calcium and magnesium ions to form insoluble carbonates, which precipitate out of the water. This method removes both temporary and permanent hardness. $$\text{Ca}^{2+}\text{(aq)} + \text{Na}_2\text{CO}_3\text{(aq)} \longrightarrow \text{CaCO}_3\text{(s)} + 2\text{Na}^{+}\text{(aq)}$$
• 3. Ion exchange method: Hard water is passed through a column containing ion-exchange resins. These resins exchange their sodium ions for the calcium and magnesium ions present in the hard water, effectively softening it. $$2\text{RNa(s)} + \text{Ca}^{2+}\text{(aq)} \longrightarrow \text{R}_2\text{Ca(s)} + 2\text{Na}^{+}\text{(aq)}$$