Question

1. 20 mL of a 10 mg/L chloroform solution in water is placed in a 40 mL vial and sealed. After equilibrium is reached, the vial is opened and the chloroform concentration in the water is found to be 8.90 mg/L

a. Use material balance to find the Henry's constant, Hc. (dimensionless)

b. What is the concentration in the gas phase in the vial?

Answer 1

mass of chloroform in aqueous phase=10mg/L *20 *10^-3 L=200 *10^-3 mg=200*10-3 mg*10^-3g/mg=200*10^-6 g

moles of chloroform in aqueous phase=mass/molar mass=200*10^-6 g/119.38 g/mol=1.68*10^-6 moles

Now , at equilibrium mass of chloroform in aqueous phase=8.9mg/L *20 *10^-3 L=178 *10^-3 mg=178*10-3 mg*10^-3g/mg=178*10^-6 g

moles of chloroform in aqueous phase=mass/molar mass=178*10^-6 g/119.38 g/mol=1.49*10^-6 moles

moles that escaped into gas phase =initial moles-equilibrium moles=1.68*10^-6 moles-1.49*10^-6 moles=0.19 *10^-6 moles

1)Hc=ca/cg=1.49*10^-6 moles/ 0.19 *10^-6 moles=7.842                                    ca=concentration in aqueous phase,cg=conc in gas phase of the species

b)concentration in the gas phase in the vial=moles/volume=0.19 *10^-6 moles /20 ml=0.0095* 10^-6 moles/ml

                                                                                          =(0.0095* 10^-6 moles * 119.38 g/mol) /ml

                                                                                         =1.13*10^-6 g/ (1 ml * 10^-3 L/ml)

                                                                                          =1.13*10^-6 g*10^3/L

                                                                                        =1.13*10^-3 g/L

                                                                                         1.13 mg/L