Chem Help Anyone?

I have a test tomorrow on this and he told that 2 of these types of questions are on it for sure and they are worth a lot and I am confused beyond all reason


1. A solution of 0.827g of an unknown non-electrolyte compound in 2.500 g of water has a freezing point of -10.18C. Calculate the molar-mass (g/mol) of the compound. HINT find molality, then solve for moles

2. A compound called pyrene has the empirical forumula C8H5. When 4.04 g of pyrene is dissolved into 10.00g of benzene, the boiling point of the solution is 85.1C. Calculate the molar-mass of pyrene nad determine its molecular formula. The molal-boiling point constant of Benzene is 2.53C/m and its normal boiling point is 80.1C

The answer to 1. is 10mph and the answer to 2. is False.

Do you still need help with these?

It's late so you're probably already offline - but I'll post this anyway. If you get this before your class, PM me and I'll send you the answer for the second question. D

My symbols aren't coming through when I paste this in from Word, so email me if you want a clearer version.

[id1b0545ffb]1. A solution of 0.827g of an unknown non-electrolyte compound in 2.500 g of water has a freezing point of -10.18C. Calculate the molar-mass (g/mol) of the compound. HINT find molality, then solve for moles [/id1b0545ffb]

Ok, as it says first find molality

Molality = (Delta)Tb/Kb
(Delta)Tb = change in freezing point, 10.18C
Kb is constant, for H20=0.52c/[id1b0545ffb]m[/id1b0545ffb]
= 10.18C/0.52 C/[id1b0545ffb]m[/id1b0545ffb]
= 19.577 [id1b0545ffb]m[/id1b0545ffb]

So, the solution contains 19.577 mol of solute per kilogram of solvent. Per the given info, the solution was prepared from 0.827g of solute and 2.5g of solvent. The number of grams of solute in a kilogram of solvent is therefore

Grams solute/Kilograms solvent = (0.827g solute X / 2.5g H20)(1000g H20 / 1kg X)
= (.3308)(1000)
= 330.8 g solution/kg H20

Since a kilogram of the solvent contains 330.8 g of solute, and the (Delta)T=19.577m (from 1st part of equation)
Molar-mass = 330.8 g / 19.577 [id1b0545ffb]m[/id1b0545ffb]
Molar-mass= 16.897 g/m

I think that's right - I just tossed it together so let me know if you don't think so.
YES, I'm a science nerd - tutored chem to pay for college. shock

[quote4274329907="syriandoode"]I have a test tomorrow on this and he told that 2 of these types of questions are on it for sure and they are worth a lot and I am confused beyond all reason


1. A solution of 0.827g of an unknown non-electrolyte compound in 2.500 g of water has a freezing point of -10.18C. Calculate the molar-mass (g/mol) of the compound. [b4274329907]HINT find molality, then solve for moles[/b4274329907]

2. A compound called pyrene has the empirical forumula C8H5. When 4.04 g of pyrene is dissolved into 10.00g of benzene, the boiling point of the solution is 85.1C. Calculate the molar-mass of pyrene nad determine its molecular formula. The molal-boiling point constant of Benzene is 2.53C/m and its normal boiling point is 80.1C[/quote4274329907]
http//www.ksr.ku.edu/libres/Mammals_of_Kansas/images/mole.JPG[" alt=""/img4274329907]
[img="4274329907]http//www.bugsandweeds.co.uk/animals/mole.jpg[" alt=""/img4274329907]

Or...

http//www.capitalcosmetic.com/images/bna/face/2/p-bef-face-mole-2.jpg[" alt=""/img365264d54c]

The teacher will probably accept either. shrug

Wow. I. Hate. Moles. I sucked at that two years ago when I took chemistry. P

I am in chemistry right now worst decsion ever seeing as how i am going to be a computer engineer and dont need chemistry really /

I think it's fun. I'm taking AP chemistry next year. I'm thinking of going into pharmacy or engineering.