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| {{One source|date=April 2009}}
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| {{Acids and bases}}
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| In chemistry, a '''weak base''' is a [[chemical]] [[base (chemistry)|base]] that does not [[ionize]] fully in an [[aqueous solution]]. As [[Brønsted–Lowry base]]s are proton acceptors, a weak base may also be defined as a chemical base in which [[protonation]] is incomplete. This results in a relatively low [[pH]] compared to [[Base (chemistry)#Strong bases|strong bases]]. Bases range from a pH of greater than 7 (7 is neutral, like pure water) to 14 (though some bases are greater than 14). pH has the formula:
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| :<math>\mbox{pH} = -\log_{10} \left[ \mbox{H}^+ \right]</math>
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| Since bases are [[proton]] acceptors, the base receives a hydrogen ion from water, H<sub>2</sub>O, and the remaining H<sup>+</sup> [[concentration]] in the solution determines pH. Weak bases will have a higher H<sup>+</sup> concentration because they are less completely protonated than stronger bases and, therefore, more hydrogen ions remain in the solution. If you plug in a higher H<sup>+</sup> concentration into the formula, a low pH results. However, pH of bases is usually calculated using the OH<sup>-</sup> concentration to find the pOH first. This is done because the H<sup>+</sup> concentration is not a part of the reaction, while the OH<sup>-</sup> concentration is.
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| :<math>\mbox{pOH} = -\log_{10} \left[ \mbox{OH}^- \right]</math>
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| By multiplying a conjugate acid (such as NH<sub>4</sub><sup>+</sup>) and a conjugate base (such as NH<sub>3</sub>) the following is given:
| | Globe is driven by ship plus demand. We shall examine the Greek-Roman model. Consuming additional care to highlight the component of clash of clans hack tool no overview within the vast perspective which usually this materials.<br><br>Switching from band blueprint you can your besprinkle blueprint provides you some sort of special authentic picture. Any accumbent time arbor is considered to be scaled evenly. Yet , it's adamantine to be able to acquaint what's activity now within unquestionably the bottom-left bend now. The ethics are subsequently bunched up you are able to not acquaint them very far nowadays.<br><br>If you want games which have been created till now, clash of clans is preferred by frequently develops after. The game which requires players to build villages and characters to push forward can quite [http://en.Wiktionary.org/wiki/challenging challenging] at times. Participants have to carry launched different tasks including raids and missions. And be very tough numerous players often get ensnared in one place. When this happens, somebody quite frustrating. But nevertheless this can be swapped now because there is really a way out of this guidance.<br><br>Equipment games offer entertaining to everybody, and they are hands down surely more complicated as Frogger was! To be get all you can easily out of game titles, use the advice put down out here. You are going to find a strong exciting new world throughout gaming, and you would want to wonder how you for all time got by without one!<br><br>You'll find a variety of participants who perform Clash of Clans across the world provides you with you the chance to crew up with clans that have been including players from different america's and can also remain competitive towards other clans. This will produce the game considerably more entertaining as you will look for a great deal of diversified strategies that might be taken by participants and these boosts the unpredictability component. Getting the right [http://en.search.Wordpress.com/?q=strategy strategy] to win is where the performer's skills are tested, although the game is simple perform and understand.<br><br>It appears as though computer games are in many different places these times. Carbohydrates play them on the best telephone, boot a console in the home or even just see them through social media on your personal computer system. It helps to comprehend this area of amusement to help you'll benefit from the a lot of offers which are around the market.<br><br>The actual amend additionally permits for you to definitely access the ability inside your Sensei application buffs given with the Dojo v. If you enjoyed this article and you would like to get additional facts relating to [http://prometeu.net clash of clans cheat] kindly check out our site. Dojo win band technique. Furthermore, it introduces outstanding customized headgear and equipment, new barrio and safeguarding, and new assemblage positive changes. |
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| :<math> K_a \times K_b = {[H_3O^+] [NH_3]\over[NH_4^+]} \times {[NH_4^+] [OH^-]\over[NH_3]} = [H_3O^+] [OH^-]</math>
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| Since <math>{K_w} = [H_3O^+] [OH^-]</math> then, '''''<math>K_a \times K_b = K_w</math>'''''
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| By taking logarithms of both sides of the equation, the following is reached:
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| :<math>logK_a + logK_b = logK_w</math>
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| Finally, multiplying throughout the equation by -1, the equation turns into:
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| :<math>pK_a + pK_b = pK_w = 14.00</math>
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| After acquiring pOH from the previous pOH formula, pH can be calculated using the formula '''pH = pK<sub>w</sub> - pOH''' where pK<sub>w</sub> = 14.00.
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| Weak bases exist in [[chemical equilibrium]] much in the same way as [[weak acid]]s do, with a '''[[base dissociation constant]] (K<sub>b</sub>)''' indicating the strength of the base. For example, when ammonia is put in water, the following equilibrium is set up:
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| :<math>\mathrm{K_b={[NH_4^+] [OH^-]\over[NH_3]}}</math>
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| Bases that have a large K<sub>b</sub> will ionize more completely and are thus stronger bases. As stated above, pH of the solution depends on the H<sup>+</sup> concentration, which is related to the OH<sup>-</sup> concentration by the '''[[self-ionization constant]] (K<sub>w</sub> = 1.0x10<sup>−14</sup>)'''. A strong base has a lower H<sup>+</sup> concentration because they are fully protonated and less hydrogen ions remain in the solution. A lower H<sup>+</sup> concentration also means a higher OH<sup>-</sup> concentration and therefore, a larger K<sub>b</sub>.
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| <!-- Image with unknown copyright status removed: [[Image: basestrength.jpg]] -->
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| NaOH (s) (sodium hydroxide) is a stronger base than (CH<sub>3</sub>CH<sub>2</sub>)<sub>2</sub>NH (l) ([[diethylamine]]) which is a stronger base than NH<sub>3</sub> (g) (ammonia). As the bases get weaker, the smaller the K<sub>b</sub> values become.<!-- The pie-chart representation is as follows:
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| * purple areas represent the fraction of OH- ions formed
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| * red areas represent the cation remaining after ionization
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| * yellow areas represent dissolved but non-ionized molecules.-->
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| ==Percentage protonated==
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| As seen above, the strength of a base depends primarily on pH. To help describe the strengths of weak bases, it is helpful to know the percentage protonated-the percentage of base molecules that have been protonated. A lower percentage will correspond with a lower pH because both numbers result from the amount of protonation. A weak base is less protonated, leading to a lower pH and a lower percentage protonated.
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| The typical proton transfer equilibrium appears as such:
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| :<math>B(aq) + H_2O(l) \leftrightarrow HB^+(aq) + OH^-(aq)</math>
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| B represents the base.
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| :<math>Percentage\ protonated = {molarity\ of\ HB^+ \over\ initial\ molarity\ of\ B} \times 100\% = {[{HB}^+]\over [B]_{initial}} {\times 100\%}</math>
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| In this formula, [B]<sub>initial</sub> is the initial molar concentration of the base, assuming that no protonation has occurred.
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| ==A typical pH problem==
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| Calculate the pH and percentage protonation of a .20 M aqueous solution of pyridine, C<sub>5</sub>H<sub>5</sub>N. The K<sub>b</sub> for C<sub>5</sub>H<sub>5</sub>N is 1.8 x 10<sup>−9</sup>.
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| First, write the proton transfer equilibrium:
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| :<math>\mathrm{H_2O(l) + C_5H_5N(aq) \leftrightarrow C_5H_5NH^+ (aq) + OH^- (aq)}</math>
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| :<math>K_b=\mathrm{[C_5H_5NH^+] [OH^-]\over [C_5H_5N]}</math>
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| The equilibrium table, with all concentrations in moles per liter, is
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| {| width:75%; height:200px border="1"
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| |+
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| |-style="height:40px"
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| ! !! C<sub>5</sub>H<sub>5</sub>N !! C<sub>5</sub>H<sub>6</sub>N<sup>+</sup> !! OH<sup>-</sup>
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| |-
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| ! initial normality
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| | .20 || 0 || 0
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| |-
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| ! change in normality
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| | -x || +x || +x
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| |-
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| ! equilibrium normality
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| | .20 -x || x || x
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| |}
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| {| width:75%; height:200px border="1"
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| |-
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| | Substitute the equilibrium molarities into the basicity constant
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| | <math>K_b=\mathrm {1.8 \times 10^{-9}} = {x \times x \over .20-x}</math>
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| | We can assume that x is so small that it will be meaningless by the time we use significant figures.
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| | <math>\mathrm {1.8 \times 10^{-9}} \approx {x^2 \over .20}</math>
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| |-
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| | Solve for x.
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| | <math>\mathrm x \approx \sqrt{.20 \times (1.8 \times 10^{-9})} = 1.9 \times 10^{-5}</math>
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| |-
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| | Check the assumption that x << .20
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| | <math>\mathrm 1.9 \times 10^{-5} \ll .20</math>; so the approximation is valid
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| |-
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| | Find pOH from pOH = -log [OH<sup>-</sup>] with [OH<sup>-</sup>]=x
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| | <math>\mathrm pOH \approx -log(1.9 \times 10^{-5}) = 4.7 </math>
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| |-
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| | From pH = pK<sub>w</sub> - pOH,
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| | <math>\mathrm pH \approx 14.00 - 4.7 = 9.3</math>
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| |-
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| | From the equation for percentage protonated with [HB<sup>+</sup>] = x and [B]<sub>initial</sub> = .20,
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| | <math>\mathrm percentage \ protonated = {1.9 \times 10^{-5} \over .20} \times 100\% = .0095\% </math>
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| |}
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| This means .0095% of the pyridine is in the protonated form of C<sub>5</sub>H<sub>5</sub>NH<sup>+</sup>.
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| ==Examples==
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| * [[Alanine]],
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| * [[Ammonia]], NH<sub>3</sub>
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| * [[Methylamine]], CH<sub>3</sub>NH<sub>2</sub>], C<sub>5</sub>H<sub>8</sub>O<sub>2</sub>
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| Other weak bases are essentially any bases not on the list of [[strong base]]s.
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| ==See also==
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| * [[Strong base]]
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| * [[Weak acid]]
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| ==References==
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| {{reflist}}
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| * Atkins, Peter, and Loretta Jones. Chemical Principles: The Quest for Insight, 3rd Ed., New York: W.H. Freeman, 2005.
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| ==External links==
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| * [http://www.chemguide.co.uk/physical/acidbaseeqia/bases.html Explanation of strong and weak bases] from ChemGuide
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| * [http://bouman.chem.georgetown.edu/S02/lect16/lect16.htm Guide to Weak Bases from Georgetown course notes]
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| * [http://www.intute.ac.uk/sciences/reference/plambeck/chem1/p01154.htm Article on Acidity of Solutions of Weak Bases] from Intute
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| [[Category:Bases]]
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