|MadSci Network: Chemistry|
I do not know how old you are or what level you are in shcool but to ask about hydrochloric acid dissolution into ions puts you at least in Jr. High School. There are two major types of chemical bonds: covalent and ionic. A covalent bond forms when the atoms involved have attractions for the bonding electron(s) that are about the same strength. The electron(s) end up being about equally shared between the atoms and a strong bond is formed. Compounds like these (sugar, oxygen, carbon dioxide, etc.) do not split into ions when they are dissolved in water. The second type of chemical bond is ionic. These bonds form between atoms that have more dissimlar attractions for the bonding electron(s). The more electronegative atom (the non-metal) will unequally take the bonding electrons. So long as the ionic compound is not dissolved in water the ions will probably stay together. Examples of ionic compounds are table salt, hydrogen chloride (HCl), etc. Your question asked why hydrochloric acid dissolves into H+ and Cl- ions when dissolved in water. Water is a covalent compound and therefore exhibits very strong bonds between the Hydrogen and Oxygen atoms. In addition, the water molecule is bent, that is, the atoms are not in a straight line, but make an angle of approximately 109 degrees. The Oxygen is still the negative part of the water molecule, so the electrons spend a little more time in orbit near the oxygen end of the molecule. This leaves the hydrogens with a slight deficiency of negative charge from the orbiting electrons. The molecule ends up with what is called a dipole. Part of the molecule has a partial negative charge while the other end has a partial positive charge. These dipoles on every water moleclue makes them very powerful agents for taking apart ionic compounds. Hydrochloric acid is no exception. The partial negative oxygen attracts and takes the H+ portion of HCl away while the partial positive Hydrogen end of the water molecule takes the Cl- ion away. Each of these ions are then surrounded by water molecules with their polar ends pointing toward each of these separated H+ and Cl- ions. This completely separates them from each other and at this point the ions are said to be dissolved. Hydrochloric acid is almost 100% dissociated into ions in water but other ionic bonded compounds may not be 100% separated. The more completely dissociated HCl is said to be a strong acid, at low concentrations, while carbonic acid H2CO3 (the acid formed when carbon dioxide CO2, is dissolved in water) is said to be a weak acid, because the hydrogens are only partly separated from their molecule. I hope this helps.
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