Concept explainers
Dimethylglyoxime [DMG, (CH3CNOH)2] is used as a reagent to precipitate nickel ion. Assume that 53.0 g of DMC has been dissolved in 525 g of ethanol (C2H5OH).
s
The red, insoluble compound formed between nickel(II)ion and dimethylglyoxime (DMG) is precipitated when DMG is added to a bask solution of Ni2+ (aq).
- (a) What is the mole fraction of DMG?
- (b) What is the molality of the solution?
- (c) What is the vapor pressure of the ethanol over the solution at ethanol’s normal boiling point of 78.4 °C?
- (d) What is the boiling point of the solution? (DMG does not produce ions in solution.) (Kbp for ethanol = +1.22 °C/m)
(a)
Interpretation: Mole fraction of DMG has to be calculated.
Concept introduction:
Raoult’s law: In a solution, vapor pressure of solvent is proportional to its mole fraction.
where,
Mole fraction: Amount of that component divided by the total amount of all of the components of the mixture
Answer to Problem 57GQ
Mole fraction of DMG is
Explanation of Solution
Given,
The number of moles of any substance can be determined using the equation
Number of moles of dimethylglyoxime is,
Number of moles of ethanol is,
Mole fraction of DMG is calculated
Mole fraction of DMG is
(b)
Interpretation: Molality of the solution has to be determined.
Concept introduction:
Raoult’s law: In a solution, vapor pressure of solvent is proportional to its mole fraction.
where,
Mole fraction: Amount of that component divided by the total amount of all of the components of the mixture
Answer to Problem 57GQ
Molality of the solution is
Explanation of Solution
Given,
The number of moles of any substance can be determined using the equation
Number of moles of dimethylglyoxime is,
Molality of the solution is calculated
Molality of the solution is
(c)
Interpretation: Mole fraction of DMG and molality of the solution are to be determined. Vapour pressure of ethanol over the solution and Boiling point of the solution are to be calculated.
Concept introduction:
Raoult’s law: In a solution, vapor pressure of solvent is proportional to its mole fraction.
where,
Mole fraction: Amount of that component divided by the total amount of all of the components of the mixture
Answer to Problem 57GQ
Vapor pressure of ethanol over the solution is
Explanation of Solution
(c)
Given,
The number of moles of any substance can be determined using the equation
Number of moles of dimethylglyoxime is,
Number of moles of ethanol is,
Mole fraction of ethanol is
Vapour pressure of ethanol over the solution is calculated
Vapour pressure of ethanol over the solution is
(d)
Interpretation: Mole fraction of DMG and molality of the solution are to be determined. Vapour pressure of ethanol over the solution and Boiling point of the solution are to be calculated.
Concept introduction:
Raoult’s law: In a solution, vapor pressure of solvent is proportional to its mole fraction.
where,
Mole fraction: Amount of that component divided by the total amount of all of the components of the mixture
Answer to Problem 57GQ
Boiling point of the solution is
Explanation of Solution
(d)
Given,
Number of moles of dimethylglyoxime is,
Molality of the solution is calculated
Molality of the solution is
Elevation in boiling point of the solution is calculated
Therefore,
Boiling point of the solution is
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