Aqua regia (royal water) is a 3:1 mixture of concentrated HCl and HNO₃. It can dissolve noble metals gold and platinum by forming complex ions. Freshly prepared, it is a fuming yellow liquid. Used in etching and cleaning.
Explanation:
Chromium (minimum 10.5%) forms a thin, adherent, transparent oxide layer (Cr₂O₃) on the surface, preventing further oxidation. Nickel adds ductility and enhances corrosion resistance. Iron is the base; carbon is for hardness but not corrosion resistance.
Explanation:
Lead-acid batteries use dilute sulfuric acid (approx 35%). During discharge, H₂SO₄ concentration decreases, forming PbSO₄ on both electrodes.
Explanation:
PVC has polar C-Cl bonds; the chlorine atoms create dipole-dipole interactions between polymer chains, restricting chain movement and making the material rigid and strong. Adding plasticizers (e.g., phthalates) reduces intermolecular forces, making it flexible. Cross-links are in thermosets, PVC is thermoplastic. High molecular weight contributes but polarity is key.
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