Magnesium chloride dissolves in water to give a faintly acidic solution (pH = approximately 6). With a large excess of water, the temperature never gets high enough for that to happen - the ions just stay in solution. On the other hand, there is no point in learning a complicated bit of chemistry if all you need is a simplification. Chlorine and argon are omitted – chlorine because it is meaningless to talk about "chlorine chloride", and argon because it doesn't form a chloride. A solution of aluminium chloride of ordinary concentrations (around 1 mol dm-3, for example) will have a pH around 2 - 3. The rest of the chlorides don't conduct electricity either solid or molten because they don't have any ions or any mobile electrons. Leaving aside the aluminium chloride and phosphorus(V) chloride cases where the situation is quite complicated, the attractions in the others will be much weaker intermolecular forces such as van der Waals dispersion forces. The structure is an ionic lattice - although with a lot of covalent character. This statement - 9.2(e) - deals with the reactions of the chlorides of the elements in Period 3 with water. This page looks at the structures of the chlorides of the Period 3 elements (sodium to sulphur), their physical properties and their reactions with water. Chemguide: Support for CIE A level Chemistry, Learning outcome 9.2(e) and part of 9.2(f). Solid phosphorus(V) chloride doesn't conduct electricity because the ions aren't free to move. Sodium and magnesium chlorides are ionic and so will undergo electrolysis when they are molten. The others are simple covalent molecules. Silicon tetrachloride is a simple no-messing-about covalent chloride. It becomes 4-coordinated - each aluminium now being surrounded by 4 chlorines rather than 6. The other chlorides all react with water in a variety of ways described below for each individual chloride. © Jim Clark 2010 (last modified January 2018). Sodium chloride dissolves in water to produce sodium ions (Na + (aq)) and chloride ions (Cl-(aq)) but neither ion reacts with water (hydrolyses) so the aqueous solution is neutral (because water … Molten aluminium chloride (only possible at increased pressures) doesn't conduct electricity because there aren't any ions any more. You should obviously check your syllabus, but you also need to look at past papers and mark schemes so that you know what your examiners are actually asking. Reactions of Chlorides with Water. Remember that we are only dealing with the chlorides: NaCl, MgCl 2, AlCl 3 / Al 2 Cl 6, SiCl 4, and PCl 5. Look at the text book suggestions page to find some of the available books. Magnesium chloride is also ionic, but with a more complicated arrangement of the ions to allow for having twice as many chloride ions as magnesium ions. Aqueous solutions of period 3 chlorides change from neutral to acidic as you go across the period from left to right. Electricity is carried by the movement of the ions and their discharge at the electrodes. The aluminium chloride reacts with the water rather than just dissolving in it. Topic: Periodicity, Inorganic Chemistry, A Level Chemistry, Singapore. Unfortunately, phosphorus(V) chloride is structurally more complicated. Check out other A Level Chemistry Video Lessons here! Use the final (combined) equation listed under phosphorus(V) chloride, producing phosphoric(V) acid and HCl. The pH of these aqueous solutions are related to the polarising power of the metal cations. If you quoted somewhere in the region of pH 1 to 3, you would be about right. Before you go on, you should find and read the statements in your copy of the syllabus. Electronegativity increases as you go across the period and, by the time you get to aluminium, there isn't enough electronegativity difference between aluminium and chlorine for there to be a simple ionic bond. As the temperature increases a bit more, it increasingly breaks up into simple AlCl3 molecules. It isn't a substitute for reading the page. It will actually depend on the concentration of the solution formed, but learn the one that you will need in the exam.). These equilibria (whichever you choose to write) lie further to the right, and so the solution formed is more acidic - there are more hydroxonium ions in it. At room temperature, think of it as being ionic with a high degree of covalent character. The formation of the ions involves two molecules of PCl5. The liquid will have van der Waals dispersion forces and dipole-dipole attractions. Sodium and magnesium chlorides are simple ionic chlorides with giant ionic structures. In the liquid (where it exists - both of these sublime at ordinary pressures), they have converted into a covalent form, and so don't conduct either. In this case the electron cloud of water molecules will be distorted to a greater extent which weakens the O-H bonds in water. Remember that we are only dealing with the chlorides: NaCl, MgCl2, AlCl3 / Al2Cl6, SiCl4, and PCl5. Do consider signing up for my A Level H2 Chemistry Tuition classes at Bishan or online chemistry classes! You should be able to explain (including equations) the reactions involving aluminium, silicon and phosphorus(V) chlorides. In a large excess of water, the hydrogen chloride will, of course, dissolve to give a strongly acidic solution containing hydrochloric acid. However, it undergoes electrolysis when the ions become free on melting. To return to the list of learning outcomes in Section 9, To return to the list of all the CIE sections. It would also be useful to look at books written specifically for your actual syllabus. Finally we can put this all together to compare the polarising power and pH trends of the Period 3 metal chlorides. It is a liquid because there are only van der Waals dispersion forces and dipole-dipole attractions between the molecules. Phosphorus(V) chloride (phosphorus pentachloride), PCl5. There is much more about this later on this page. You get phosphorous acid, H3PO3, and fumes of hydrogen chloride (or a solution containing hydrochloric acid if lots of water is used). Sodium: The reaction is vigorous and the sodium melts and floats on the water. You may also find the last equation in a simplified form: Hydrogen ions in solution are hydroxonium ions. As an approximation, the simple ionic chlorides (sodium and magnesium chloride) just dissolve in water. In the magnesium case, the amount of distortion is quite small, and only a small proportion of the hydrogen atoms are removed by a base - in this case, by water molecules in the solution.