Which solution has the highest vapor pressure?

a.) 20.0 g of gluclose (C6H12O6) in 100.0 mL of water

b.) 20.0 g of sucrose (C12H22O11) in 100.0 mL of water

c.) 10.0 g of potassium acetate (KC2H3O2) in 100 mL of water

the highest vapor pressure is the solution (b) P = 23.552 torr

∴ sln (a) : P = 23.33 torr

∴ sln (c) : P = 23.370 torr

Explanation:

vapor pressure:

ΔP = - (P*a) (Xb, l) = P - P*a

∴ a: solvent (water)

∴ b: solute

assuming T=25°C:

∴ P*a (25°C) = 23.8 torr

molecular weight:

∴ Mw H2O = 18 g/mol

∴ Mw glucose: 180.156 g/mol

∴ Mw sucrose = 342.3 g/mol

∴ Mw potassium acetate = 98.15 g/mol

∴ mol H2O = (100 mL) (1 g/mL) (mol/18 g) = 5.55 mol H2O

a) moles glucose = (20.0 g) (mol/180.156 g) = 0.111 mol

⇒ Xb, l = (0.111 mol C6H12O6) / (5.55 + 0.111) = 0.0196

⇒ ΔP = - (23.8 torr) (0.0196) = - 0.466 torr = P - P*a

⇒ P = 23.8 torr - 0.466 torr = 23.33 torr

b) moles sucrose = (20 g) (mol/342.3 g) = 0.0584 mol

⇒Xb, l = (0.0584) / (5.55 + 0.0584) = 0.0104

⇒ ΔP = - (23.8 torr) (0.0104) = - 0.248 torr

⇒ P = 23.8 torr - 0.248 torr = 23.552 torr

c) moles KC2H3O2 = (10 g) (mol/98.15 g) = 0.102 mol

⇒ Xb, l = (0.102) / (5.55 + 0.102) = 0.0180

⇒ ΔP = - (23.8 torr) (0.0180) = - 0.429 torr

⇒ P = 23.8 torr - 0.429 torr = 23.370 torr