Dimethylglyoxime, DMG, is an organic compound used to test for aqueous nickel(II) ions. A solution prepared by dissolving 65.0 g of DMG in 375 g of ethanol boils at 80.3°C. What is the molar mass of DMG? Kb = 1.22°C/m, boiling point of pure ethanol = 78.5°C

117.5 g/mol.

Explanation:

ΔTb = Kb · bB

where,

ΔTb = the boiling point elevation = Tb (solution) - Tb (pure solvent).

Kb = the ebullioscopic constant

bB = the molality of the solution

ΔTb = 80.3 - 78.5

= 1.8 °C

1.8 = 1.22 x bB

= 1.475 mol/kg

Molality is the number of moles of the solute divided by the mass of the solvent.

Number of moles solute = 1.475 * 0.375

= 0.55 mol

Molar mass = mass/number of moles

= 65.0/0.55

= 117.5 g/mol.

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