Mada za sehemu hiiCompounds Of MetalsMada 6
Chlorine can react with all metals to form chlorides. Most common metals are attacked by dilute hydrochloric acid to form chlorides. Examples are Mg, Ca, Al, Zn, and Fe.
Those elements (metals) which are not attacked by dilute carbonates or oxides of these metals react with dilute HCl (hydrochloric acid) to produce chlorides.
Metallic chlorides can be prepared by direct or indirect methods.
By direct method
Chloride can be prepared by direct action of chlorine on metals.
Iron(III) chloride can be prepared by passing Cl₂ over a heated metal. An iron wire is placed in a hard glass tube and a stream of dry Cl₂ passes over it. The reaction continues without further application of heat source and iron(III) chloride collects in a bottle as shown.
Soluble chlorides are usually prepared using dilute hydrochloric acid (HCl) and a suitable metal, metal oxide, hydroxide, or carbonate. The method depends on the reactivity of the metal involved.
| Metal | Method of Preparation | Example Equation |
|---|---|---|
| Potassium (K) | React potassium oxide, hydroxide, or carbonate with HCl | KOH + HCl → KCl + H₂O |
| Sodium (Na) | React sodium oxide, hydroxide, or carbonate with HCl | Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ |
| Calcium (Ca) | React calcium oxide or carbonate with HCl | CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ |
| Magnesium (Mg) | React magnesium metal, oxide, or carbonate with HCl | Mg + 2HCl → MgCl₂ + H₂ |
| Aluminium (Al) | React aluminium metal, oxide, or hydroxide with HCl | 2Al + 6HCl → 2AlCl₃ + 3H₂ |
| Zinc (Zn) | React zinc metal, oxide, or carbonate with HCl | ZnO + 2HCl → ZnCl₂ + H₂O |
| Iron (Fe) | React iron metal or oxide with HCl | Fe + 2HCl → FeCl₂ + H₂ |
Insoluble chlorides are usually prepared by a method called precipitation. This involves mixing two solutions that react to form an insoluble salt (precipitate) and a soluble salt.
General method (ionic precipitation)
This method involves mixing:
A soluble chloride (e.g., sodium chloride, NaCl)
with
A soluble salt of another metal that forms an insoluble chloride
Example
Lead(II) chloride (PbCl₂) is an insoluble salt and can be prepared by mixing:
Lead(II) nitrate (Pb(NO₃)₂)
Sodium chloride (NaCl)
Equation: Pb(NO₃)₂ (aq) + 2NaCl (aq) → PbCl₂ (s) + 2NaNO₃ (aq)
In this reaction:
PbCl₂ forms as a white precipitate (insoluble)
NaNO₃ remains dissolved in water (soluble)
Other examples
- Silver chloride AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)
- Mercury(I) chloride Hg₂(NO₃)₂ (aq) + 2NaCl (aq) → Hg₂Cl₂ (s) + 2NaNO₃ (aq)
- To identify a chloride in a liquid mixture, add silver nitrate (AgNO₃). A white precipitate forms.
- To identify a chloride from a solid mixture, add concentrated sulphuric acid. The gas that produces thick white fumes with ammonium solution is produced.
- Mix chloride with an oxidizing agent (MnO₂). A greenish-yellow gas is evolved.
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