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Slightly soluble compounds - definition

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Definition of Slightly Soluble

A substance is classified as slightly soluble when it dissolves in a solvent, but only to a limited extent. It is considered slightly soluble if one part of the solute dissolves in 100 to 1,000 parts of the solvent. These substances form a solution with some dissolved material but often leave behind undissolved particles.

Characteristics of Slightly Soluble Substances

  • Limited dissolution in a solvent.
  • May result in a cloudy solution due to undissolved particles.
  • Precipitates when solubility limits are exceeded.
  • Solubility is influenced by temperature, pH, and the presence of other chemicals.

Examples of Slightly Soluble Compounds

1. Everyday Slightly Soluble Compounds

  • Calcium hydroxide (Ca(OH)2) – Used in limewater, dissolves only slightly in water.
  • Magnesium hydroxide (Mg(OH)2) – Active ingredient in antacids like milk of magnesia.
  • Silver chloride (AgCl) – Forms a white precipitate, slightly soluble in water.
  • Barium sulfate (BaSO4) – Used in medical imaging, very low solubility.
  • Calcium carbonate (CaCO3) – Found in limestone and chalk, slightly soluble in water.

2. Slightly Soluble Pharmaceuticals

  • Paracetamol (C8H9NO2) – Limited solubility affects its absorption in the body.
  • Aspirin (C9H8O4) – Dissolves slowly in water but more readily in stomach acid.
  • Ibuprofen (C13H18O2) – Poorly water-soluble, affecting its dissolution rate.

3. Slightly Soluble Minerals

  • Hydroxyapatite (Ca10(PO4)6(OH)2) – Main component of bones and teeth.
  • Lead(II) sulfate (PbSO4) – Forms in lead-acid batteries, affecting performance.
  • Iron(III) hydroxide (Fe(OH)3) – Used in water purification.

Factors Influencing the Solubility of Slightly Soluble Substances

1. Temperature

For some substances, increasing temperature enhances solubility, but for others, like calcium carbonate, solubility decreases with rising temperature.

2. pH of the Solution

Acidic conditions can increase the solubility of certain compounds. For example, CaCO3 dissolves in acidic solutions due to the formation of soluble bicarbonate ions.

3. Presence of Complexing Agents

Certain slightly soluble salts dissolve more in the presence of ligands that form soluble complexes. Example: AgCl dissolves in NH3 due to complex ion formation.

4. Pressure (For Gases in Liquids)

Pressure has little effect on solids but significantly affects gases dissolved in liquids.

Applications of Slightly Soluble Compounds

1. Medicine and Pharmaceuticals

  • Slow-dissolving drugs enable controlled drug release.
  • Barium sulfate (BaSO4) is used in medical imaging due to its low solubility.
  • Hydroxyapatite in teeth and bones ensures durability due to its controlled solubility.

2. Water Treatment and Environmental Science

  • Iron hydroxides help remove heavy metals from water.
  • Calcium carbonate maintains pH balance in natural water bodies.

3. Industrial and Chemical Applications

  • Cement and concrete production rely on slightly soluble calcium compounds.
  • Lead sulfate formation in batteries affects efficiency.

4. Geological and Biological Significance

  • Mineral deposits such as limestone contain slightly soluble compounds.
  • Calcium carbonate influences ocean chemistry and carbon cycling.

Conclusion

Slightly soluble substances play essential roles in nature, industry, and medicine. Their controlled solubility is crucial for applications ranging from drug formulation to water treatment. Understanding their behavior helps optimize various processes in science and engineering.