2 Learning objectives After reviewing this presentation learner will be able toTell the properties of Hydrogen chlorideDescribe the preparatory methods of Hydrogen chlorideExplain the chemical properties of Hydrogen chloride
3 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.
4 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 singlebond.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.
5 H2O and HCl combine to form hydronium cations, H3O+ and chloride anions ,Cl– through a reversible chemical reaction:HCl + H2O → H3O+ + 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 + CH3OH → CH3O+H2 + Cl–
6 Preparation of HCl Direct synthesis Brine (mixture of sodium chloride and water) solution is electrolyzed producing chlorine (Cl2), sodium hydroxide, and hydrogen (H2).The pure chlorine gas can be combined with hydrogen to produce hydrogen chloride.Cl2(g) + H2(g) → 2 HCl(g)
7 Preparation of HCl Laboratory method i) It is prepared industrially by the combustion of Hydrogen, H2, in Chlorine, Cl2.H2 + Cl HClii) Hydrogen Chloride may be prepared in the laboratory by heating Concentrated Sulphuric Acid, with Sodium Chloride.NaCl + H2SO4 → NaHSO4 + HClThis reaction occurs at room temperature. Provided there is salt remaining in the generator and it is heated above 200 degrees Celsius, the reaction proceeds toNaCl + NaHSO4 → HCl + Na2SO4
8 Preparation of HCliii) The chlorides of non-metals (e.g. Phosphorus trichloride, PCl3) 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.PCl3 + 3H2O H3PO3 + 3HClPhosphorus pentachloride, is hydrolysed by hot water, to give Orthophosphorus Acid, (i.e. Phosphoric(V)Acid) and Hydrogen Chloride. PCl5 + 4H2O H3PO4 + 5HClPhosphorus pentachloride, is also hydrolysed by cold Water, to give Phosphorus oxychloride.PCl5 + H2O → POCl3 + 2 HCl
9 Reactions of HCl i) Reaction with ethyne: Ethyne, reacts with Hydrogen Chloride, very slowly.HC=CH + HCl H2C=CClEthyneH2C=CCl + HCl H3C-CCl21,1 dichloroethaneii) Reaction with ethanolEthanol, reacts with Hydrogen Chloride, to form Ethylchloride, (i.e. chloroethane) and water. A dehydratingagent (e.g. Zinc Chloride) is used.ZnCl2C2H5OH + HCl C2H5Cl + H2Ethanol Ethyl chloride
10 Reactions of HCl iii) Reaction with Potassium permanganate: Chlorine, may also be prepared by dropping cold concentrated Hydrochloric Acid, on Potassium permanganate.2KMnO4 + 16HCl MnCl2 + 2KCl + 8H2O + 5Cl2iv) Reaction with Manganese dioxideThe most common laboratory method for preparation ofchlorine, is to heat 100 gm. of Manganese dioxide, with300 ml. of concentrated Hydrochloric Acid.MnO2 + 4 HCl MnCl2 + 2 H2O + Cl2