Question

NEED HELP ASAP!
Calculate the molality of C2H5OH in a water solution that is prepared by mixing 50.0 mL of C2H5OH with 138.2 mL of H2O at 20 degrees Celsius. The density of the C2H5OH is 0.789 g/mL at 20 degrees Celsius.
A. 0.00620
B. 8.4
C. 0.161
D. 6.20
E. none of these

Answer 1

1.- calculate the mass of C2H5OH with the density value and the volume given in the problem. density = mass/volume => mass = density x volume

2.-Then you can calculate the molecular mass of C2H5OH from the atomic mass of each element (from periodic table)

3.-Then you can calculate how many moles you have in that mass "moles = mass/molecular mass C2H5OH"

4.- consider the density of water as a 1g/ml. Convert the mL of water to g then to kg.

5.- To find the molality that is the number of moles of solute per 1000 g solvent you have to divide the number of moles calculate in step 3 by the mass of water in kg (step 4)