how would I find the mass of something from the molality.....
How many grams of water should be added to 25.0 g of NaCl to produce a 0.450 m solution?
CC--Definitions, definitions, definitions.
molality = moles/kg solvent
You want 0.45 m and you want 25.0 g NaCl.
How many moles is 25.0 g NaCl? That will be moles = grams/molar mass.
25.0/58.5 (the 58.5 is an estimate) = 0.43 moles. Now substitute that into the definition for molal.
0.45 m = 0.43 mols/kg
solve for kg. (I rounded the 0.43 moles also).
I got it its 950 g
To find the mass of something from its molality, you need to know the molality itself, the molar mass of the substance, and the mass of the solvent.
In this case, you want to find the mass of water that should be added to 25.0 g of NaCl to produce a 0.450 m solution.
First, we need to understand what molality (m) is. Molality is defined as the number of moles of solute per kilogram of solvent. In this case, the solute is NaCl, and the solvent is water.
To calculate the molality (m), use the formula:
m = moles of solute / mass of solvent (in kg)
We are given that the molality (m) is 0.450 m. This means that there are 0.450 moles of NaCl per kilogram of water.
Next, we need to find the moles of NaCl. To calculate the moles, use the formula:
moles = mass of NaCl / molar mass of NaCl
The molar mass of NaCl is the sum of the atomic masses of sodium (Na) and chlorine (Cl). The atomic mass of Na is 22.99 g/mol, and the atomic mass of Cl is 35.45 g/mol. Therefore, the molar mass of NaCl is 22.99 + 35.45 = 58.44 g/mol.
Now, we can calculate the moles of NaCl:
moles = 25.0 g / 58.44 g/mol
Once you have the moles of NaCl, you can determine the mass of water needed by rearranging the molality formula:
mass of solvent = moles of solute / molality
mass of solvent = (moles of NaCl) / (molality)
mass of solvent = (25.0 g / 58.44 g/mol) / 0.450 m
Finally, convert the mass of solvent to grams:
mass of water = (mass of solvent) x 1000 g/kg
This will give you the mass of water that should be added to 25.0 g of NaCl to produce a 0.450 m solution.