Confusing Equations from TPR

[sanguinee]

---

Members don't see this ad.

So I was doing some drills on TPR and came across two equations that I haven't seen before/ don't really know where they would be applied.

Didn't find anything on this equation, it was relations to salts:
ΔTb = kbim). All of the salts have an i = 2 except for Na2CO3 (i = 3).

And I don't really understand what this equation is for:
difference in pressure between two points in a static fluid is given by the expression pfluidgy,
where y is the vertical distance between the two points


Any help would be very much appreciated!

 

[NextStepTutor_2]

These are both useful equations! The first one relates to colligative properties, specifically boiling point elevation. Basically, whenever you add a nonvolatile solute to a solvent, the boiling point of that solvent will increase proportionally to the number of solute particles added. ΔTb refers to the increase in boiling point, kb is a constant (they'll give this to you), "i" refers to the number of particles per molecule of solute, and "m" is molality. A similar equation is ΔTb = kfim, which gives you a similar colligative property, freezing point depression.

The second equation is even more commonly used on the exam. For example, they might ask you to find the pressure in a tank of water 10 m below its surface. The pressure at the surface is simply atmospheric P, while the pressure at 10 m is P (atm) + p(fluid)*g*y. This means that pressure is directly proportional to both fluid density and depth. (They could also ask less mathematical and more conceptual questions, such as "if you double the depth, how does pressure change," etc.)

 

[NextStepTutor_2]

Oh, and back to your point about the value of i for specific salts - the reason why i = 3 for Na2CO3 is simply that sodium carbonate dissociates into 3 particles in water (2 Na+ and 1 CO3 2-). NaCl, on the other hand, would have i = 2 because it just dissociates into one Na+ cation and one Cl- anion. These are both ionic compounds, so they dissociate in water! They could also ask you to evaluate boiling point elevation for a molecule like glucose, which is covalent and thus doesn't break apart at all in water. So for glucose, i = 1.