Question

How many grams of water are needed to dissolve 27.8g of NH4NO3 (80.0 g/mol) in order to prepare a 0.452 m (molal) solution?

27.8g / 80g/mol X 0.452 = 0.157

Is this correct?

Answer 1

I think you algebra is off somewhere. Moles is correct but not kg solvent.
27.8 g/80 = ? moles.
m = ?moles/kg solvent
Solve for kg solvent.
You can check yourself to see if it is right. 27.8/80 = about 0.35
0.35/0.157 = about 2.2m which isn't 0.452.

Answer 2

the answer choices that were given are:

a)769g
b)36.2g
c)972g
d)34.8g
e)157g

Answer 3

I can assure you that 157 g is not right.
C'mon Hannah, do the math.
27.8/80 = ?mols
m = moles/kg solvent so
kg solvent = moles/m and that isn't 0.157 kg.

Answer 4

27.8/80=0.3475 but I don't understand what to do next.

Answer 5

You have 27.8 g NH4NO3.
mol NH4NO3 = 27.8/80 = 0.3475
You want a molality of 0.452
m = 0.452 = moles/kg solvent
0.452 = 0.3475/kg solvent
Solve for kg solvent.
Then since the answers are given in grams, you will need to convert kg solvent to g solvent.

Answer 6

Ok thank you