Answer:
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.
In the given case, the molar mass of Dimethylglyoxime is - 117.48 g / mol
Given:
Kb = 1.22°C/m
boiling point of pure ethanol = 78.5°C
solution of DMG in ethanol boils = 80.3°C
Solution:
We know that Colligative Property problems can be solved by the following equation:
dTb = Kb × m
Where
Tb = elevation in boiling point
= boiling point of solution - boiling point of pure ethanol
= 80.3 - 78.5
= 1.8 degree Celsius
and, Kb = elevation in boiling point constant
= 1.22 degree C / m
=> m = molality of the solution
= [tex]\frac{( mass\ / Molar\ mass )}{weight\ of\ the\ solvent\ in\ Kg}[/tex]
= [tex]\frac{65 / M }{0.375}[/tex]
By using the above values
1.8 = [tex]1.22 \times \frac{65 / M }{0.375}[/tex]
M = 117.48 g/mol
Thus, In the given case, the molar mass of Dimethylglyoxime is - 117.48 g / mol
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