Chemistry!?

Question

What will be the freezing point depression if 42.0 g of ibuprofen (C13H18O2) is dissolved in 975 g of naphthalene? Kf for naphthalene is 7.00˚C/m

What is the boiling point elevation of 200. g of water when 11.4 g of ammonia (NH3) is dissolved in it? The Kb of water is .52˚C/m.

When 2.04 g of a substance were dissolved in 7.84 g of solvent, the freezing point decreased by 3.5˚C. The Kf for the solvent is 2.8˚C/m. What is the molar mass of the substance?

A solution is prepared using 18.0 g of an unknown substance in 150.0 g water. The boiling point was elevated .34˚C from that of pure water. The Kb for water is .52˚C/m. Calculate the molar mass of that substance.

What mass of ethylene glycol (C2H6O2, molar mass 62.1 g/mol) must be added to 10.0 kg water to produce a solution that freezes at-10.0°C? Kf for water is 1.86C/m.

What is the molar mass of 10 g of an unknown substance that raises the boiling point of .250 kg of water .75˚C? The Kb for water is .52˚C/m.

Answer 1

First, let me probably sound rude and say that this isn't the best way to get help here. It looks like you just want someone else to do your homework for you.

If you have specific questions, I'd be more than happy to help. So, for all of these problems, you'll be using a single equation that should be in your notes or book that is something like:

DT = km where DT is the change in the freezing or boiling point of a solution, k is either kb or kf and m is the molality of the solution. Molality is defined as moles of solute per kilogram of solvent. So, convert your mass of solute into moles and divide by the mass of the solvent in kilograms to calculate your molality. Then, multiply that value by the k for the solvent. Finally either add that to or subtract that from the normal boiling or freezing point of the solvent and you're good.

Now, you can work these problems in various directions, finding the mass which will lower the freezing point....

Just work with them a while...If you have a specific question, ask...