Chemistry equilibrium??? ksp?

[xuxiwen]

Write the Ksp expression for lead chromate (PbCrO4) and calculate its solubility in mol/L. Ksp=2.3 *10^-13

I don't really understand what Ksp is or how to do it??? please help thanks!

[Vanamonde]

Well guy, you're not the first person to confuse Kerbal Space Program with the solubility product constant, but maybe somebody here can answer the question for you anyway. :D

[K^2]

Lead chromate dissociates according to the following equilibrium equation.

PbCrO[sub]4[/sub] ⇌ Pb[sup]2+[/sup] + CrO[sub]4[/sub][sup]2-[/sup]

Any time you see dissociation of the form A[sub]p[/sub]B[sub]q[/sub] ⇌ pA + qB, you can write down K[sub]sp[/sub] = [A][sup]p[/sup][B][sup]q[/sup]. Because you just end up with one of each ion here, you have a very simple case p = q = 1.

K[sub]sp[/sub] = [Pb[sup]2+[/sup]][CrO[sub]4[/sub][sup]2-[/sup]]

Solubility is defined as number of moles of original compound A[sub]p[/sub]B[sub]q[/sub] that can dissolve in a liter of water. Therefore, by definition, solubility S = [A]/p = [B]/q.

Solving this together with the general expression for K[sub]sp[/sub] above, one may derive the general expression for solubility.

S = (K[sub]sp[/sub] / (p[sup]p[/sup] q[sup]q[/sup]) ) ^ (1/(p+q))

I hope you can substitute in the numbers and get the answer yourself. I would also strongly advise trying to solve this problem for other compounds, where p and q are not 1. If you can't do these, you should talk to you teacher/professor/TA, because otherwise, you'll be in serious trouble at the exam. Edited November 18, 2015 by K^2

[xuxiwen]

so confuse?????

[RainDreamer]

[URL]http://chemwiki.ucdavis.edu/Physical_Chemistry/Equilibria/Solubilty/Solubility_Product_Constant,_Ksp[/URL]

[QUOTE][COLOR=#333333][FONT=Arial]The solubility product constant, [/FONT][/COLOR][COLOR=#333333][FONT=Arial][FONT=MathJax_Math-italic]K[/FONT][FONT=MathJax_Math-italic]s[/FONT][FONT=MathJax_Math-italic]p[/FONT][/FONT][/COLOR][COLOR=#333333][FONT=Arial]​,[/FONT][/COLOR][COLOR=#333333][FONT=Arial] is the equilibrium constant for a solid substance dissolving in an aqueous solution. It represents the level at which a solute dissolves in solution. The more soluble a substance is, the higher the [/FONT][/COLOR][COLOR=#333333][FONT=Arial][FONT=MathJax_Math-italic]K[/FONT][FONT=MathJax_Math-italic]s[/FONT][FONT=MathJax_Math-italic]p[/FONT][/FONT][/COLOR][COLOR=#333333][FONT=Arial] value it has.[/FONT][/COLOR][/QUOTE]

I don't have any knowledge about chemistry, real far out of my field, but I supposed from what I read, sugar has much higher Ksp than plastic, for example. Edited November 19, 2015 by RainDreamer

[K^2]

[quote name='xuxiwen']so confuse?????[/QUOTE]
That doesn't tell any of us which parts you don't understand. Can you be more specific? Do you understand what notation [Pb[sup]2+[/sup]] means, for example? Do you know what dissociation means? If none of this rings a bell, you probably need to go back to either your textbook or get help from teacher/professor/TA for your class. If you can follow some of this, we might be able to help with the rest. But not without knowing where you get stuck.