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Strong acids and bases will dissociate completely (acids into H3O+ and based into OH-). There are 7 main strong acids. Strong bases are comprised of Group 1 and 2 oxides/hydroxides (use the periodic table).
The strength of an acid or base is determined by its ability to dissociate in water. A strong acid would completely dissociate in the water, yielding a hydronium ion of the same concentration as the concentration of the acid itself. For example, HCl would dissociate completely into hydrogen and chlorine atoms, however, since the hydrogen atoms cannot be present in their free form in water, they will be picked up by water molecules, yielding hydronium ions which are H3O+. If there is 1 mole of HCl, it will completely dissociate into 1 mole of chloride and 1 mole of hydronium ions because it is a strong acid. If it was a weak acid, it would not completely dissociate, and there wouldn't be exactly 1 mole of hydronium ions, rather there would be less. The dissociation of a weak acid is incomplete and is shown by its K value. Strong acids have an almost infinite K value due to the fact that their reactant concentration which is in the denominator is almost zero as it has dissociated completely into its components. Because they have a large K value (Concentration of products/concentration of reactants), they are usually not shown. However, because weak acid have small K values, they are usually given in a question. The same goes for bases. Strong bases completely dissociate, yielding OH- ions of the same concentration as the base itself. So, the strength of an acid or a base depends on its dissociation into its components which determines the concentration of hydronium or hydroxide it will release into the solution. This dissociation can be determined looking at the electronegativities of the atoms hydrogen or hydroxide is bound to, or the bond length. For example, HF is a weaker acid than HCl because fluorine is more electronegative than chlorine and therefore it is harder for fluorine to release hydrogen into the solution than chlorine. The bond length between fluorine and hydrogen is also shorter due to the fact that fluorine has a smaller radius. Because smaller bonds are stronger than longer bonds, HF has more difficulty dissociating than HCl.
Weak acids and bases will incompletely dissociate/ionize. To represent this in a chemical reaction, you would write an equilibrium equation and use the concentrations of reactants and products to determine what percent ionized. equilibrium constant (K) = [products]/[reactants]
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