Calculate the molar solubility of PbCrO4 in: (a) Pure Water (d) 1.0 x 10^-3 M K2CrO4

Video transcript

Hello. In this problem we are asked what are the liabilities of copper to oxalate in pure water? And in a 2.5 times 10 demise three molar sodium oxalate solution. We'll begin by considering just pure water. So write our equation then that describes the equilibrium between our solid proper to oxalate and its ions. And we'll set up a nice tables. We have initial change in equilibrium so we'll ignore our solid since it won't appear in our equilibrium constant expression. Initially we have no copper ions or oxalate and ions to changes in its plus X plus X. The equilibrium then is the initial and the change so we have X. And X. So our celebrity product constant then is equal to the concentration of our copper ions times the oxalate and this is equal to X times X. So we have X squared. Then it's equal to 4.43 Times 10 -10. So extend is equal to the square root of this. So x. works out then to two 10 times 10 to -5 smaller. So this is then the more solid ability of copper to oxalate in pure water. Next we'll consider then the miller sorry ability of property oxalate in a solution of sodium oxalate, sodium oxalate is a soluble salt. So it will associate completely then to form it's irons in a quick solution We're told that the concentration of the sodium oxalate is 2.5 Times to the -3 levels per leader. Given that in the reaction we have one mole of sodium oxalate produced one mole of oxalate irons. That means that the concentration of sodium oxalate will be equal to the concentration of our oxalate anons. We'll set up the ice table again, beginning with our equation for opportunity in equilibrium with the lions and we have initial change in equilibrium. So again, we'll ignore the solid initially have no copper ions, but now we do have oxalate antigens due to the presence of our sodium oxalate solution. And so this is what we refer to as the common iron effect. So the change then is plus X plus X, equilibrium, then is initial plus a change. This is X. And then 2.5 times 10 to the minus three plus X. Since we're dealing with a fairly insoluble salt, the scalability product constant is the order of 10 to the minus 10. X is going to be small relative to the 2.5 times 10 minus three. So we'll just approximate this. Then it's 2.5 times 10 to the minus three and drop our X. Our scalability product constant. Then we have the concentration of our copper lines times out of our oxalate and turns and this works out to X 10 times 2.5 times 10 to the minus three. This is equal to 4.43 times 10 to the minus russell Kerekes. That works out then to 1.8 Percent of -7 Moller. This is then the scalability of cop to oxalate In a solution of sodium oxalate. We found that the scalability decreased in the presence of a common iron. Thanks for watching. Hope this helped.