WCLN Ionization of Water Chemistry

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Shows how water ionizes to form hydronium and hydroxide ions • Gives the ionization equation for water • Defines Kw and shows the Kw expression • Defines neutral, acidic, and basic solutions • http://www.BCLearningNetwork.com. • 0:00water is usually thought of as a • 0:05nonconductor however very sensitive • 0:07devices can detect some conductivity and • 0:10water no matter how period is even very • 0:14pure distilled water contains some ions • 0:16why is this so in any sample of pure • 0:20water almost all of the water molecules • 0:22remain as neutral water molecules and • 0:24don't react chemically with each other • 0:27however about two out of every five • 0:29hundred and fifty six million water • 0:31molecules will react chemically with • 0:34each other will show two of them here • 0:36but they're bonding and non-bonding • 0:38electrons • 0:40the purple one will act as an acid and • 0:43the blue one will act as a base • 0:46the hydrogen atom breaks away from the • 0:49water on the left and leaves it shared • 0:51electron behind • 0:53because it has lost an electron requires • 0:56a positive charge becoming an H+ ion or • 0:59proton • 1:01because the o.h is gained an electron it • 1:04requires a negative charge and it's • 1:06called the hydroxide ion • 1:09with the formula or h minus the proton • 1:12moves to a nonbonding electron pair on • 1:15the other water molecule will change its • 1:18color to blue • 1:19the positive charge is now distributed • 1:21over the whole iron instead of just • 1:24being on the H that it came with • 1:26this is now a hydronium ion with the • 1:29formula h3o plus • 1:33the process can be summarized by an • 1:35equation when a proton is transferred • 1:38from one water molecule to another the • 1:41water on the Left gains a proton to • 1:43become a hydronium ion and the water on • 1:46the right loses a proton to become a • 1:48hydroxide ion • 1:50however when a hydronium ion in water • 1:52encounters a hydroxide ion the reverse • 1:55reaction can also occur where a proton • 1:58is transferred from the hydronium ion to • 2:01the hydroxide • 2:03forming two molecules of water because • 2:06both the forward and reverse reactions • 2:08continuously occur this is an • 2:11equilibrium so we use a double arrow • 2:13here instead of writing these two • 2:16separate water molecules we can combine • 2:18them to show them simply as two water • 2:21molecules • 2:23remove this arrow over a bit this • 2:26equation is very important equation to • 2:28know it's called the ionization of water • 2:31equation • 2:32sometimes it's called the self • 2:34ionization of water because water acts • 2:37as both the acid and the base in • 2:40chemistry 12 we refer to it simply as • 2:43the ionization of water • 2:45at a normal room temperature of 25 • 2:47degrees the reactant liquid water is • 2:50highly favorite to illustrate this we • 2:53show there's more reactants and products • 2:56the relative sizes of the letters here • 2:58are very qualitative and nowhere near to • 3:01scale the concentration of hydronium and • 3:04hydroxide ions are only about two • 3:06billions that of water • 3:09the KQ expression for this reaction is • 3:11equal to the concentration of hydronium • 3:13times the concentration of hydroxide • 3:16because the water is a liquid it is not • 3:19included in the KQ expression • 3:22because this equilibrium constant is • 3:24specifically concerned with water we • 3:27change the symbol from KQ to kW kW is • 3:32called the ionization constant of water • 3:35the value for KW his • 3:38temperature-dependent at 25 degrees the • 3:41value is 1 times 10 to the negative 14 • 3:43is very important to remember the value • 3:47of K W is 1 times 10 to the negative 14 • 3:50only at 25 degrees celsius and no other • 3:54temperature • 3:56but KW is always equal to the • 3:58concentration of hydronium times the • 4:00concentration of hydroxide at any • 4:03temperature for which water is in the • 4:05liquid state because all equal solutions • 4:08contain water and all water ionizers to • 4:11form some hydronium and hydroxide ions • 4:14we know that all aqueous solutions • 4:17contain some hydronium and some • 4:19hydroxide ions by definition for any • 4:22aqueous solution if the concentration of • 4:25hydronium is equal to the concentration • 4:27of hydroxide the solution is set to be • 4:30neutral and if the concentration of • 4:32hydronium is greater than the • 4:34concentration of hydroxide the solution • 4:37is set to be acidic and if the • 4:39concentration of hydronium is less than • 4:41the concentration of hydroxide solution • 4:44is set to be basic these are the • 4:47definitions will use for neutral acidic • 4:50and basic solutions you must make sure • 4:52that you know these

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