Question

Number 3

2. Calculate AVmix, A Hmix, ASmix, and AG mix for mixing 2 moles of argon, 1 mole of helium, and 3 moles of hydrogen gas carried out under constant conditions of 1 atm and 298 K. Assume ideal behavior. Vem mol- 3. Shown is the graph of partial molar volumes (in cmº/mol or mL/mol) of water (A) and methanol (B) solutions at 25°C: a. From the graph, what are the molar volumes of pure water and pure methanol? b. Derive the densities of water and methanol from your answer in (a). C. Estimate the final volume of a solution formed by mixing 50 mL of methanol with 50 mL water. Justify the result based on the intermolecular forces present in the methanol-water solution. 1 O 0.2 0.4 0.6 0.8 1.0 XB

Answer 1

Q3 (a)

Molar volume of pure water = 18 ml /mol

Molar volume of methanol = 38ml /mol

(b )

1 mole of water has 18g mass

Molar mass of methanol = 12 +4 + 16= 32g/mol

Density of water = 18g/18ml = 1 g/ml

Density of methanol = 32g/38ml = 0.8421g/ml.

(c)

Mass of 50ml water = 50ml × 1g/ml = 50g

Mass of 50ml methanol = 50ml × 0.8421g/ml = 42.105g

Moles fraction of methanol = (42.105/32)/(42.105/32 + 50/18) = 0.32143

Final volume of solution = 17.8ml/mol × (50/18)mol + 38.8ml/mol × (42.105/32) = 49.778 ml + 51.0526 ml = 100.497ml

∆V_mix > 0 , that means solution shows positive deviation from the ideal behavior . That means the intermolecular forces of attraction between water and methanol is not that much stronger as intermolecular forces of attraction between water molecules .

Water-water interactions are stronger than water-methanol interactions . Hence positive deviation .