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? K_b = 1.22°C/m, boiling point of pure ethanol = 78.5°C A)44.1 g/mol B)65.8 g/mol C)117 g/mol D)131.6 g/mol E)553 g/mol

Question

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First, we need to calculate the boiling point elevation of the solution compared to pure ethanol:

ΔT = i*K*m
where ΔT is the boiling point elevation, i is the van't Hoff factor (the number of particles into which DMG dissociates in solution, which we will assume to be 1), K is the molal boiling point constant of the solvent (ethanol), and m is the molality of the solution.

We can calculate m as follows:

m = moles of DMG / mass of solvent (in kg)

To calculate the moles of DMG, we need to use the given amount of DMG and its formula:

65.0 g DMG / (2*14.01 g/mol + 4*12.01 g/mol + 4*1.01 g/mol + 2*16.00 g/mol) = 0.319 mol DMG

Now we can calculate the molality:

m = 0.319 mol / 0.375 kg = 0.850 m

Finally, we can calculate the boiling point elevation:

ΔT = 1 * 1.22°C/m * 0.850 m = 1.04°C

The boiling point of the solution is therefore:

boiling point = 80.3°C + 1.04°C = 81.3°C

To calculate the molar mass of DMG, we can use the formula for the boiling point elevation of a nonvolatile solute:

ΔT = K*m*(1 - (1/moles of solute)*mass of solvent/(molar mass of solute))

Solving for the molar mass of DMG:

molar mass of DMG = mass of solute / moles of solute

mass of solute = 65.0 g
moles of solute = 0.319 mol
mass of solvent = 375 g
K = 1.22°C/m
ΔT = 1.04°C
boiling point of pure solvent = 78.5°C

Substituting into the formula and solving:

1.04 = 1.22*(0.850)*(1 - (1/0.319)*0.375/molar mass of DMG)
molar mass of DMG = 117 g/mol

Dimethylglyoxime, DMG, Is an Organic Compound Used to Test for Aqueous