Presentation on theme: "Hydrogen chloride. Learning objectives After reviewing this presentation learner will be able to Tell the properties of Hydrogen chloride Describe the."— Presentation transcript:
Learning objectives After reviewing this presentation learner will be able to Tell the properties of Hydrogen chloride Describe the preparatory methods of Hydrogen chloride Explain the chemical properties of Hydrogen chloride
Hydrogen chloride The compound hydrogen chloride has the formula HCl. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. The formula HCl is often used to refer, somewhat misleadingly, to hydrochloric acid, an aqueous solution that can be derived from hydrogen chloride.
Properties of Hydrogen chloride Hydrogen chloride is composed of diatomic molecules, each consisting of a hydrogen atom H and a chlorine atom Cl connected by a covalent single bond. Since the chlorine atom is much more electronegative than the hydrogen atom, the covalent bond between the two atoms is quite polar. Consequently, the molecule has a large dipole moment with a negative partial charge δ – at the chlorine atom and a positive partial charge δ + at the hydrogen atom.
H 2 O and HCl combine to form hydronium cations, H 3 O + and chloride anions,Cl – through a reversible chemical reaction: HCl + H 2 O → H 3 O + + Cl – The resulting solution is called hydrochloric acid and is a strong acid. Hydrogen chloride can dissolve in certain other solvents such as methanol, protonate molecules or ions, and serve as an acid-catalyst for chemical reactions where anhydrous (water-free) conditions are desired. HCl + CH 3 OH → CH 3 O + H 2 + Cl –
Preparation of HCl Direct synthesis Brine (mixture of sodium chloride and water) solution is electrolyzed producing chlorine (Cl 2 ), sodium hydroxide, and hydrogen (H 2 ). The pure chlorine gas can be combined with hydrogen to produce hydrogen chloride. Cl 2 (g) + H 2 (g) → 2 HCl(g)
Preparation of HCl Laboratory method i) It is prepared industrially by the combustion of Hydrogen, H 2, in Chlorine, Cl 2. H 2 + Cl 2 2 HCl ii) Hydrogen Chloride may be prepared in the laboratory by heating Concentrated Sulphuric Acid, with Sodium Chloride. NaCl + H 2 SO 4 → NaHSO 4 + HCl This reaction occurs at room temperature. Provided there is salt remaining in the generator and it is heated above 200 degrees Celsius, the reaction proceeds to NaCl + NaHSO 4 → HCl + Na 2 SO 4
Preparation of HCl iii) The chlorides of non-metals (e.g. Phosphorus trichloride, PCl 3 ) are covalent compounds. These chlorides fume in air and are readily hydrolysed to yield either an acid or an acidic oxide. For example, Phosphorus trioxide, reacts with the Moisture, in air to form Phosphorous Acid, and Hydrogen Chloride. PCl 3 + 3H 2 O H 3 PO 3 + 3HCl Phosphorus pentachloride, is hydrolysed by hot water, to give Orthophosphorus Acid, (i.e. Phosphoric(V)Acid) and Hydrogen Chloride. PCl 5 + 4H 2 O H 3 PO 4 + 5HCl Phosphorus pentachloride, is also hydrolysed by cold Water, to give Phosphorus oxychloride. PCl 5 + H 2 O → POCl HCl
Reactions of HCl i ) Reaction with ethyne: Ethyne, reacts with Hydrogen Chloride, very slowly. HC=CH + HCl H 2 C=CCl Ethyne H 2 C=CCl + HCl H 3 C-CCl 2 1,1 dichloroethane ii) Reaction with ethanol Ethanol, reacts with Hydrogen Chloride, to form Ethyl chloride, (i.e. chloroethane) and water. A dehydrating agent (e.g. Zinc Chloride) is used. ZnCl 2 C 2 H 5 OH + HCl C 2 H 5 Cl + H 2 Ethanol Ethyl chloride
Reactions of HCl iii ) Reaction with Potassium permanganate: Chlorine, may also be prepared by dropping cold concentrated Hydrochloric Acid, on Potassium permanganate. 2KMnO HCl 2MnCl 2 + 2KCl + 8H 2 O + 5Cl 2 iv) Reaction with Manganese dioxide The most common laboratory method for preparation of chlorine, is to heat 100 gm. of Manganese dioxide, with 300 ml. of concentrated Hydrochloric Acid. MnO HCl MnCl H 2 O + Cl 2