Hard

• phosphate


  PO₄³⁻
• thiosulfate


  S₂O₃²⁻
• hydrogen phosphate


  HPO₄²⁻
• dichromate


  Cr₂O₇²⁻
• chromate


  CrO₄²⁻
• carbonate


  CO₃²⁻
• sulfate


  SO₄²⁻
• sulfite

  SO₃²⁻
• sulfide

  S²⁻
• dihydrogen phosphate


  H₂PO₄⁻
• acetate


  CH₃COO⁻
• permanganate


  MnO₄⁻
• hypochlorite


  OCl⁻
• chlorate


  ClO₃⁻
• hydrogen sulfate


  HSO₄⁻
• hydrogen sulfite

  HSO₃⁻
• hydrogen sulfide


  HS⁻
• hydrogen carbonate

  HCO₃⁻
• nitrate

  NO₃⁻
• nitrite


  NO₂⁻
• hydronium

  H₃O⁺