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The extent to which the vapor pressure of a solvent is lowered and the boiling point is elevated depends on the total number of solute particles present in a given amount of solvent, not on the mass or size or chemical identities of the particles. A 1 m aqueous solution of sucrose (342 g/mol) and a 1 m aqueous solution of ethylene glycol (62 g/mol) will exhibit the same boiling point because each solution has one mole of solute particles (molecules) per kilogram of solvent.

Calculating the boiling point of a solution

What is the boiling point of a 0.33 m solution of a nonvolatile solute in benzene?

Solution

Use the equation relating boiling point elevation to solute molality to solve this problem in two steps.

This is a diagram with three boxes connected with two arrows pointing to the right. The first box is labeled, “Molality of solution,” followed by an arrow labeled, “1,” pointing to a second box labeled, “Change in boiling point,” followed by an arrow labeled, “2,” pointing to a third box labeled, “New boiling point.”
  1. Calculate the change in boiling point.
    Δ T b = K b m = 2.53 ° C m −1 × 0.33 m = 0.83 ° C
  2. Add the boiling point elevation to the pure solvent’s boiling point.
    Boiling temperature = 80.1 ° C + 0.83 ° C = 80.9 ° C

Check your learning

What is the boiling point of the antifreeze described in [link] ?

Answer:

109.2 °C

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The boiling point of an iodine solution

Find the boiling point of a solution of 92.1 g of iodine, I 2 , in 800.0 g of chloroform, CHCl 3 , assuming that the iodine is nonvolatile and that the solution is ideal.

Solution

We can solve this problem using four steps.

This is a diagram with five boxes oriented horizontally and linked together with arrows numbered 1 to 4 pointing from each box in succession to the next one to the right. The first box is labeled, “Mass of iodine.” Arrow 1 points from this box to a second box labeled, “Moles of iodine.” Arrow 2 points from this box to to a third box labeled, “Molality of solution.” Arrow labeled 3 points from this box to a fourth box labeled, “Change in boiling point.” Arrow 4 points to a fifth box labeled, “New boiling point.”
  1. Convert from grams to moles of I 2 using the molar mass of I 2 in the unit conversion factor.
    Result: 0.363 mol
  2. Determine the molality of the solution from the number of moles of solute and the mass of solvent, in kilograms.
    Result: 0.454 m
  3. Use the direct proportionality between the change in boiling point and molal concentration to determine how much the boiling point changes.
    Result: 1.65 °C
  4. Determine the new boiling point from the boiling point of the pure solvent and the change.
    Result: 62.91 °C
    Check each result as a self-assessment.

Check your learning

What is the boiling point of a solution of 1.0 g of glycerin, C 3 H 5 (OH) 3 , in 47.8 g of water? Assume an ideal solution.

Answer:

100.12 °C

Got questions? Get instant answers now!

Distillation of solutions

Distillation is a technique for separating the components of mixtures that is widely applied in both in the laboratory and in industrial settings. It is used to refine petroleum, to isolate fermentation products, and to purify water. This separation technique involves the controlled heating of a sample mixture to selectively vaporize, condense, and collect one or more components of interest. A typical apparatus for laboratory-scale distillations is shown in [link] .

Figure a contains a photograph of a common laboratory distillation unit. Figure b provides a diagram labeling typical components of a laboratory distillation unit, including a stirrer/heat plate with heat and stirrer speed control, a heating bath of oil or sand, stirring means such as boiling chips, a still pot, a still head, a thermometer for boiling point temperature reading, a condenser with a cool water inlet and outlet, a still receiver with a vacuum or gas inlet, a receiving flask for holding distillate, and a cooling bath.
A typical laboratory distillation unit is shown in (a) a photograph and (b) a schematic diagram of the components. (credit a: modification of work by “Rifleman82”/Wikimedia commons; credit b: modification of work by “Slashme”/Wikimedia Commons)

Oil refineries use large-scale fractional distillation to separate the components of crude oil. The crude oil is heated to high temperatures at the base of a tall fractionating column , vaporizing many of the components that rise within the column. As vaporized components reach adequately cool zones during their ascent, they condense and are collected. The collected liquids are simpler mixtures of hydrocarbons and other petroleum compounds that are of appropriate composition for various applications (e.g., diesel fuel, kerosene, gasoline), as depicted in [link] .

Questions & Answers

what is a solution
Joy Reply
A liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).
Gabby
what is an acid and base
Joy
acids are substances that ionize (break off) in an aqueous solution to produce hydrogen (H+) ions. pH level less than 7  bases produce hydroxide (OH-) ions in solution. pH level greater than 7
Gabby
An acid is a substances when dissolve in water to produce hydrogen ion as the only positive ion or proton. while base is a substances when dissolve in water to produce hydroxide ion .
Lawal
acid is a substance that produce hydrogen ion as only positive ion when dissolve in water
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the relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers.
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A radioactive subtance has a half life of 20hrs what fraction of the original radioactive nuclear will remain in 80hrs
Onyewuchi Reply
1/16th
Ian
general properties of transition metal
Abdullahi Reply
form stable complexes Have high melting and boiling points Contain large charge/radius ratio Form compounds which are often paramagnetic Are hard and possess high densities Form compounds with profound catalytic activity Show variable oxidation states form coloured ions and compounds.
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A coordinate covalent bond, also known as a dative bond or coordinate bond is a kind of 2-center, 2-electron covalent bond in which the two electrons derive from the same atom.
dharshika
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In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry. It is published in the Nomenclature of Organic Chemistry
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law of definite proportion
Victor Reply
Law of Definite Proportion states that all pure samples of the same chemical compound contains the same elements in proportion by mass
Eunice
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It is that branch of Science which deals with the study of composition, structure and properties of matter .... Ok
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The branch of natural science that deals with the constitution of substances and the changes that they undergo as a consequence of alterations in the constitution of their molecules
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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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