Learn Unit I: Chemical Substances - Nature and Behaviour with Free Lessons & Tips

Physical properties of carbon compounds or covalent compounds: Some physical properties of carbon compounds or covalent compounds include:

• Low melting and boiling points
• Often exist as gases, liquids, or solids at room temperature
• Non-conductive of electricity in the solid state
• Often have low solubility in water
• May exhibit a wide range of colors, odors, and textures

• Cinnabar and Extraction of Metal:

  • Cinnabar is mercury sulfide (HgS), a naturally occurring ore of mercury.
  • Metal is extracted from cinnabar through the process of roasting, followed by reduction with carbon or hydrogen.
  • During roasting, cinnabar is heated in the presence of oxygen to form mercury oxide (HgO), which is then reduced to elemental mercury (Hg) using carbon or hydrogen as reducing agents.
  • Overall reaction:
    • 2HgS(s) + 3O2(g) → 2HgO(s) + 2SO2(g)
    • 2HgO(s) + C(s) → 2Hg(l) + CO2(g)

• Identification of Metal A and Amphoteric Oxide B:

  • Metal A used in the thermite process is iron (Fe).
  • Oxide B is iron(III) oxide (Fe2O3), which is amphoteric in nature.
  • Reactions of oxide B with HCl and NaOH:
    • With HCl: Fe2O3(s) + 6HCl(aq) → 2FeCl3(aq) + 3H2O(l)
    • With NaOH: Fe2O3(s) + 6NaOH(aq) → 2Na3Fe(OH)6

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• A milkman adds a small amount of baking soda to fresh milk to shift the pH of fresh milk from 6 to slightly alkaline because alkaline conditions inhibit the growth of bacteria and help to preserve the freshness of milk. Baking soda (sodium bicarbonate) acts as a buffer, helping to maintain the pH of milk and prolong its shelf life.

• Acids do not show acidic behavior in the absence of water because the characteristic properties of acids, such as the donation of hydrogen ions (H+) and the ability to react with bases, depend on the presence of water molecules to facilitate proton transfer reactions. In the absence of water, acids cannot ionize and exhibit their acidic properties.

• Rainwater conducts electricity because it contains dissolved ions and gases from the atmosphere, such as carbon dioxide (CO2), oxygen (O2), and nitrogen oxides (NOx), which act as electrolytes and facilitate the flow of electric current. Distilled water, on the other hand, does not conduct electricity because it lacks dissolved ions and gases, making it a poor conductor of electricity.