Exam Preparation

[alexidior]

Hi,

I have a Chemistry exam in 2 weeks and was hoping to get some help with questions I'm going through from previous years exams that were were given without answers and I'm stuck on.

Comments

[smokeline]

Not sure about the first question, but as for the second question...

You are correct that vapor pressure decreases after the addition of a solute; in particular, it decreases based on the number of moles of a solute. Since all the masses of the alcohols are the same, you are adding fewer moles of the heavier alcohol. You should be able to use that idea to rank them.

[babyfood22]

For the first one, I would say that these are strong electrolytes, pretty much fully dissociated. This means you can approximate that they're additive, ie:

Conductivity = (nu_+ * lamda_+) + (nu_- * lamda_-)

That was awful. Sorry, no idea how to type in maths here. What I'm attempting to say is that lamda(CsF) = lamda(Cs) + lamda(F), and for all the others similarly. Therefore using this approximation, lamda(CsF) = lamda(CsNO3) - lamda(HNO3) + lamda(HF).

There's a different approximation for the limit of a weak electrolyte, in case you're interested. Ask your tutor/lecturer which you need to know or be able to derive - seriously, don't be scared to send them an email. Or just read up on it anyway if you think you have the time - more knowledge is never a bad thing when the exams are set right. Hope your exams go well!