CaCO3

CaCO3 = calcium carbonate. Key quick notes for exams: - Formula and molar mass - CaCO3 - Molar mass ≈ 100.09 g/mol - Structure and forms - Carbonate ion: CO3^2− is planar and trigonal (sp2). - Calcium ions: Ca^2+ lattice with carbonate groups. - Polymorphs/minerals: calcite (trigonal/rhombohedral, the most common), aragonite (orthorhombic, less stable at room temp), and a less common vaterite form. - Important properties - Very low solubility in water. - Common minerals: limestone (rock), marble (metamorphosed limestone), chalk. - Reactivity with acids: effervesces with HCl and other acids. - Solubility and equilibria - Dissolution: CaCO3(s) ⇌ Ca^2+(aq) + CO3^2−(aq) - Ksp at 25°C: about 3.3 × 10^−9 - In pure water, an approximate solubility would suggest [Ca^2+] ≈ [CO3^2−] ≈ sqrt(Ksp) ≈ 5–6 × 10^−5 M, but actual dissolution is affected by carbonate speciation (CO3^2− ↔ HCO3^− ↔ H2CO3/CO2) and CO2 in solution. - Reactions you should know - With acids: CaCO3 + 2 H^+ → Ca^2+ + CO2 + H2O (effervescence) - With strong acids in water: same net reaction as above; dissolves readily. - With CO2 in water: CaCO3 + CO2 + H2O ⇌ Ca(HCO3)2 (calcium bicarbonate) — this is the dissolution mechanism in natural waters and weathering; Ca(HCO3)2 is soluble. - Thermal decomposition (calcination): CaCO3(s) → CaO(s) + CO2(g) at high temperature (~900–1000°C); endothermic; used to make lime. - Basic lab/industrial uses: formation of CaO for cement/lime, neutralization of acidity (soil, flue gas), filler in paints/paper, antacid (calcium carbonate tablets). - Occurrence and uses - Abundant in rocks (limestone, marble), shells, teeth of marine organisms. - Major industrial uses: cement and concrete (as limestone and as a source of CaO after calcination), dietary/calcium supplement, agricultural lime to neutralize soil acidity, filler/piller in various products. - Quick exam-style practice - Write the balanced equation for CaCO3 reacting with hydrochloric acid. - CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) - What happens when CaCO3 is heated? - It thermally decomposes to CaO and CO2: CaCO3(s) → CaO(s) + CO2(g) - If a bottle contains only CaCO3 and water with air containing CO2, what species primarily forms in solution? - Calcium bicarbonate, Ca(HCO3)2, via CaCO3 + CO2 + H2O ⇌ Ca(HCO3)2 (soluble) - The solubility product (Ksp) indicates what about CaCO3’s solubility? - Very low solubility; at 25°C Ksp ≈ 3.3 × 10^−9. In pure water, approximate solubility would put [Ca^2+] around 10^−5 M in the absence of CO2, but actual solubility is higher in the presence of CO2 due to bicarbonate formation. If you want, I can tailor this to a specific topic (mineralogy, inorganic chemistry, environmental geochemistry, or industrial applications) or provide more practice questions and worked solutions. What would you like to focus on?