Okay so I got:

delta temp (-1.5) = (2 ions) (x molality) (-1.86) ----> (-1.5) = -3.72 (x molalitry) ------> (-1.5) / (-3.72) = (x molality) -----> molality = .403 moles per kg

Is this correct? What's next?

This post was edited by chicano on Jun 29 2015 07:18pm

The question asks for mass percentage of KBr in the water

that molar amount of KBr has a mass
and you already know there is 1kg of water

I don't know what to do next. KBr has an atomic weight of 119.0023

Am I supposed to multiply .403 by 119.0023??

Yeah to get the mass, remember?

Mass = Molecular weight *moles

Okay so

(.403 moles per kg) x (119.0023 atomic mass of KBr) = 47.9579 grams

1000 grams in a kg.

Would this mean 4.79579% is the mass percent?

You will have to do of mixture entirely.

So in 1 kg of water, there is also 0.403 moles (45.9579 grams) of KBr (or so you calculated). That should be taken into account when determining the mass percent, not just that of the water.

This post was edited by cialda on Jun 30 2015 06:29am

OKay got that last one, here is another one but this one deals with electrons, wavelength, and such:


If you hit the surface of Copper with a photon of energy and find that the ejected electron has a wavelength of .8 nm, what is the frequency of the incoming photon in Megahertz?


What I know:
.8nm = 8 x 10 ^-10 meters
Copper has an ionization energy of 745 kj or 745,000 joules


I don't know where to go from here?

energy needed to eject an electron from the surface of copper = E = hv

so frequency = E/h = 1.132 MHz

Im not sure why u are given the wavelength of the electron, unless i have forgotten something

0.8*10^-10 = h/p where p = particle momentum (mass*velocity)

from p we can calculate the kinetic energy of the electron E=(p^2)/2

????????

This post was edited by ArnoldChlamydia on Jul 1 2015 04:54pm

Doubt it. Although the professor is quite the ahole when it comes to writing questions.

How sure are you of this answer?