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?
the answer choices that were given are:
a)769g
b)36.2g
c)972g
d)34.8g
e)157g
27.8/80=0.3475 but I don't understand what to do next.
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.
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.
Ok thank you
To find out if your calculation is correct, let's break it down step by step:
Firstly, we need to calculate the number of moles of NH4NO3 required to prepare the solution. To do this, we divide the given mass (27.8g) by the molar mass of NH4NO3 (80g/mol):
27.8g / 80g/mol = 0.3475 mol
Next, we use the molality formula to determine the amount of water needed. The molality formula is:
molality (m) = moles of solute / mass of solvent (in kilograms)
Since we're given the molality (0.452 m) and we need to find the mass of the solvent (water), we rearrange the formula:
mass of solvent (in kilograms) = moles of solute / molality
mass of solvent = (0.3475 mol) / (0.452 mol/kg)
mass of solvent = 0.768 kg
Finally, to convert the mass of the solvent from kilograms to grams, we multiply by 1000:
mass of solvent = 0.768 kg * 1000 = 768g
Therefore, the correct amount of water needed to dissolve 27.8g of NH4NO3 to prepare a 0.452 m solution is 768 grams, not 0.157 grams.
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.