Question

Which of the following ideal aqueous solutions will show maximum boiling point.
(1) 0.5 M NaCl showing 50% dissociations
(2) 0.3 M K2Fe[Fe(3N)6]
(3) 1 M Glucose solution
(4) 1 mole of AgCl is mixed with 0.5 l of H2O

well i think answer should be 4. but it is 2. plz explain.

Answer 1

the amount that a solution changes its boiling point will be determined by the TOTAL number of solute particles that get dissolved in the solution. I'm going to use different numbers, but the point is the same.

If you have 1 mole of NaCl dissolving in 1L of water, you'd think you have 1 mole of solute, but since NaCl dissociates in water, you really have 2 moles of IONS:\[NaCl(aq) \rightarrow Na^{+1}(aq) + Cl^{-1}(aq)\]Each unit of NaCl creates 2 ions when it dissolves (and dissociates).

If you have 1 mole of CaCl2 dissolved in 1L of water, you might also think that you have just 1 mole of solute, but in reality we have more like THREE:
\[CaCl_2(aq) \rightarrow Ca^{+2}(aq) + 2Cl^{-1}(aq)\] Each unit of CaCl2 creates 3 ions.

So the total number of solute particles present in a solution will depend on what the substance is, and how many pieces it can dissociate into.

Now let's look at the exact solutions you have:
0.5MNaCl dissolves into 1.0M of ions, but it's only 50% dissociated

0.3M K2Fe[Fe(3n)6] disocates into THREE ions taking that concentration and tripling it

1.0M glucose doesn't dissociate at all, so you still have 1.0M solute

AgCl isn't soluble in water to any large extent, so the number of actual ions in that solution is incredibly small. The largest product of concentration and total ions is choice (b)

Answer 2

well i think there are 4 ions in 2. and how do i know agcl isnt soluble in water to a large extent? isnt it an ionic compound? that would make it as completely dissociated.

Answer 3

ionic compounds containing silver are almost never soluble. That's a property of silver compounds that we usually have to learn, or be informed of

Answer 4

hmm. got it. but there are 4 ions in 2 right?

Answer 5

@JFraser ?

Answer 6

the Fe[Fe(N3)6] is really 1 complex ion, with a -2 charge, but essentially, yes. You'll get either 3 or 4 ions out of that molecule