_____________________ is a carbonate of lead and it forms the base of lead Paints.
🔬 Understanding the Chemistry of Paint Bases
The question asks to identify a specific chemical compound: a "carbonate of lead." This chemical identity is the key to distinguishing between different types of paint bases, especially the traditional ones.
Base: The primary solid pigment in a paint that provides opacity (hiding power) and forms the main body of the paint film. Different bases have different chemical compositions.
⚖️ Detailed Analysis of the Options
Let's examine the chemical nature of each option.
(c) White lead
Chemical Composition: Basic lead carbonate, with the approximate formula 2PbCO₃·Pb(OH)₂.
Why it's correct: As its chemical name shows, white lead is fundamentally a carbonate of lead. It was historically the most important white pigment and base for oil paints due to its excellent opacity and the durable, flexible film it helped create, especially on wood.
(a) Lithopone
Chemical Composition: A mixture of barium sulfate (BaSO₄) and zinc sulfide (ZnS).
Why it's incorrect: Lithopone contains no lead and is not a carbonate. It is a white pigment but has lower hiding power than white lead or titanium white.
(b) Titanium white
Chemical Composition: Titanium dioxide (TiO₂).
Why it's incorrect: This is an oxide of titanium, not a carbonate of lead. It is the most widely used white pigment today due to its superior opacity and non-toxic nature.
(d) Red lead
Chemical Composition: Lead tetraoxide (Pb₃O₄).
Why it's incorrect: Red lead is an oxide of lead, not a carbonate. Its primary use is as a reddish-orange, anti-corrosive primer for steel, not as a white base for general paints.
💡 Study Tips for Paint Bases
- Associate the Chemistry:
- White lead = Lead Carbonate
- Red lead = Lead Oxide (for rust)
- Titanium white = Titanium dioxide (modern choice)
- Carbonate vs. Oxide: This is the key chemical distinction in the question. White lead is the carbonate; red lead is the oxide.
- White vs. Red Application: Remember their primary uses. White lead was for general painting (especially wood). Red lead is for priming steel.