PbBr2---> Pb + 2Br
Ksp=[Pb][2Br]^2
6.60× 10^–6=[x][2x]^2
Solving for x
6.60× 10^–6=4x^3
6.60× 10^–6/4=x^3
(6.60× 10^–6/4)^1/3=x
B.)
PbBr2---> Pb + 2Br
Ksp=[Pb][2Br]^2
6.60× 10^–6=[x][0.500M]^2
Solve for x,
6.60× 10^–6/[(0.500M)^2]=x
C.)
PbBr2---> Pb + 2Br
Ksp=[Pb][2Br]^2
6.60× 10^–6=[0.500M][2x]^2
Solve for x,
6.60× 10^–6/[(0.500M)^2]=x
6.60× 10^–6/(0.500M)=4x^2
sqrt*{[6.60× 10^–6/(0.500M)]/4}=x
The Ksp of PbBr2 is 6.60× 10^–6.
What is the molar solubility of PbBr2 in pure water?
What is the molar solubility of PbBr2 in 0.500 M KBr solution?
What is the molar solubility of PbBr2 in a 0.500 M Pb(NO3)2 solution?
4 answers
I don't disagree with any of the answers. Technically, and I realize this is nit-picking, I disagree with the set up. As an example,
PbBr2 ==> Pb^2+ + 2Br^-
But Ksp says "the product of the molar solubility of the ions, each raised to the power indicated in the balanced equation, is a constant". I would write that as Ksp = (Pb^2+)(Br^-)^2. It isn't twice the bromide ion x lead ion, it is THE bromide x lead ion. Yes, Pb ion is x and Br is 2x but 2x is THE bromide ion, not twice the bromide, but it is twice the PbBr2 that dissolves which is why it's 2x to begin with.
PbBr2 ==> Pb^2+ + 2Br^-
But Ksp says "the product of the molar solubility of the ions, each raised to the power indicated in the balanced equation, is a constant". I would write that as Ksp = (Pb^2+)(Br^-)^2. It isn't twice the bromide ion x lead ion, it is THE bromide x lead ion. Yes, Pb ion is x and Br is 2x but 2x is THE bromide ion, not twice the bromide, but it is twice the PbBr2 that dissolves which is why it's 2x to begin with.
I understand. That is why I worked on a problem and developed a headache when I couldn't figure out why the answer doubled compared to the answer that I calculated. If I set up the way that you mentioned then I would not have ran into that problem, and I can prevent others from performing the same mistake. Thank you for the advice. Also, I do not consider it nit-picking. I always thought it was nick-picking. We learn something new everyday.
I lent my sleeping bag to a co-worker once, when I used it the next night I woke up suddenly, feeling something crawling in my crotch. I spent the next 2 hours picking the critters off. then I went cross eyed picking nits. I got them all. Unpicked nits can grow into a HUGE problem. Never think you are being to thorough, especially in chemistry!!
1 answer