You know molality = # mols/kg solvent. Rearrange that to # mols = molality x kg solvent. Call that equation 1.
You know # mols = grams/molar mass. Call that equation 2.
Now set # mols in equation 1 = # mols in equation 2 and substitute.
molality x kg solvent = g/molar mass OR
molality x kg solvent x molar mass = grams.
You have molality desired, kg solvent, and molar mass. Solve for grams.
Post your work if you get stuck.
kg solvent x molality x molar mass = grams.
____?____g of glucose C6H12O6 must be dissolved in 400 g of water to give a solution that is 0.258 m(molality).
3 answers
Here is variation of the method offered by DrBob:
0.258m means 0.258 moles / kg of water. Based on that we can set up and solve for x:
**0.258 mol/1 kg = x / 0.400 kg
[Note: 400g = 0.400 kg]
**Solving for x gives us the moles of glucose to be used.
**Calculate the molar mass of C6H12O6 and multiply it by the value of "x" to get the grams of glucose to be added to the 400g of water.
0.258m means 0.258 moles / kg of water. Based on that we can set up and solve for x:
**0.258 mol/1 kg = x / 0.400 kg
[Note: 400g = 0.400 kg]
**Solving for x gives us the moles of glucose to be used.
**Calculate the molar mass of C6H12O6 and multiply it by the value of "x" to get the grams of glucose to be added to the 400g of water.
thanks i got it
1 answer