<p>How can Ba(OH)2, CaOH, Sr(OH)2, and Mg(OH)2 be strong bases if they do not dissolve all the way? </p>
<p>Strong bases completely dissociate. How can something completely dissociate if it doesn’t completely dissolve?</p>
<p>the dissociation process is affected by the solubility of the compound. each alkaline earth metal has something called a transcongrex vector which determines how they dissolve in pyrogenic and/ or superfluous liquids. even though the compounds you listed have dissimilar dissolving characterstics, their transcongrex vector number is the same;therefore, making them all strong bases.</p>
<p>^^ i ran a google search for “transcongrex” and cannot get a single hit. i’m suspicious. did you pull that out of a hat?</p>
<p>thats what my teacher has taught us so far</p>
<p>mayb its her name for a different concept</p>
<p>i took ap chem and never heard that word. can you give me a pg. # in a textbook which contains this word. you sound convincing but my searches are null.</p>
<p>or maybe your teacher is lying 
when i took ap chem at the end of the year the teacher tried scaring us by telling us that he taught us everything wrong. off course he was joking.</p>
<p>See, if something doesn’t fully dissolve, then how can it’s ions be assumed to be fully dissociated? If you have a strong base that’s x molar, you can say the molarity of the OH- is x.</p>
<p>This doesn’t seem logical to me as all the ions aren’t dissociated. I’ll remember these compounds are strong bases, but I would just like to know why.</p>
<p>In our AP Chem class, Ba, Ca, and Sr bases are strong (fully ionize). Mg is considered weak, but one of the stronger ones of the weak(i.e. high Kb value).</p>
<p>The hydroxides of the alkaline earth metals are slightly insoluble, so not all of it dissolves. The part that does dissolve, however, dissociates completely, which is why they’re considered strong bases.</p>
<p>The slight insolubility of these compounds does affect the OH concentration, but for the purposes of high school and general chemistry, the difference is not enough to matter.</p>
<p>Besides, solubility is arbitrary. If it’s as little as you imply it is, it wouldn’t even affect your significant figures.</p>
<p>The question of strong versus weak isn’t black and white, its a continuum. Even “completely soluble” bases like sodium hydroxide are not infinitely soluble - all salts have some limit to their solubility. “Strong bases” are those bases that, at reasonable concentrations, dissolve completely. “Reasonable concentrations” for acids and bases are often considered to be on the order of 0.1M. If you calculate the molar solubility of Ba(OH)2 from its Ksp, it’s slightly over 0.1M. If you calculate the molar solubility of Ca(OH)2 from its Ksp, it’s slightly under 0.1M. In other words, at any concentration up to around 0.1M, they <em>do</em> completely dissolve. It isn’t until concentrations are greater than 0.1 M that they dissolve (dissociate) less than 100%.
From a practical standpoint, if they ask you the pH of a Ca(OH)2 solution, treat it as a solubility problem if they provide you the Ksp and find the exact [OH-] with an icebox. Treat it as a strong base if they don’t provide a Ksp and assume it all dissociates.</p>