Molality (1 Viewer)

[lilchezza]

Can anyone by any chance help me with this;

Commercial 0.100M nitric acid is labelled as having a density of 1.005 g/mL. Take molar mass of nitric acid = 61 g/mol. The molality of the solution is:

a) 0.102 m
b) 0.101 m
c) 0.100 m
d) 0.0950 m
e) 0.103 m

 

[Rekkusu]

First thing to pick up is: Think of Density.

m = mass
d = density
v = volume

mass = density x volume

(1) d = m/v
(2) Next remember the numer of moles is equal to?

Next step...Molality = Moles of Solute / Solvent (i.e. Water) in Kg.

Now, commerical industries need to dilute the nitric acid to make the correct concentration (hint hint: water). Can you see the connection here?

I'm not sure if School of Chemistry still offers this but everyday at 1pm-2pm, a tutor is there to help people out.

 

[Tim035]

Off the top of my head, Molality= moles in 1kg of solution.

Now the solution has a density of 1.005g per ml. So 1kg of solution is going to be a tad under 1L, so the answer will be a tad under the molarity concentration. So without doing any calculations at all my guess would be- D.
But hey... what do I know.

Sort of throws you off how all the answers except D are above 0.1 m.
Is 'take the molar mass of HNO3 to be 61g" part of the question or did you add it in?