Question 11.11: USING BOILING-POINT ELEVATION TO CALCULATE THE MOLALITY OF A...

USING BOILING-POINT ELEVATION TO CALCULATE THE MOLALITY OF A SOLUTION

What is the molality of an aqueous glucose solution if the boiling point of the solution at 1 atm pressure is 101.27 °C? The molal boiling-point-elevation constant for water is given in Table 11.4.

TABLE 11.4 Molal Boiling-Point-Elevation Constants ( $K_{b}$ ) and Molal Freezing-Point-Depression Constants ( $K_{f}$ ) for Some Common Substances

Substance

K_{b}

[(°C · kg)/mol]

K_{f}

[(°C · kg)/mol]

Benzene (

C_{6}H_{6}

) 2.64 5.07
Camphor (

C_{10}H_{16}O

) 5.95 37.8
Chloroform (

CHCl_{3}

) 3.63 4.70
Diethyl ether (

C_{4}H_{10}O

) 2.02 1.79
Ethyl alcohol (

C_{2}H_{6}O

) 1.22 1.99
Water (

H_{2}O

) 0.51 1.86

STRATEGY
Rearrange the equation for molal boiling-point elevation to solve for m:

ΔT_{b}  =  K_{b}  ·  m               so                m  =  \frac{ΔT_{b}}{K_{b}}

where $K_{b}$ = 0.51 (°C · kg)/mol and $ΔT_{b}$ = 101.27 °C – 100.00 °C = 1.27 °C.

The blue check mark means that this solution has been answered and checked by an expert. This guarantees that the final answer is accurate.
Learn more on how we answer questions.

Related Answered Questions

Question: 11.14

USING OSMOTIC PRESSURE TO CALCULATE THE MOLECULAR MASS OF A SOLUTE A solution prepared by dissolving 20.0 mg of insulin in water and diluting to a volume of 5.00 mL gives an osmotic pressure of 12.5 mm Hg at 300 K. What is the molecular mass of insulin? STRATEGY To determine molecular mass, we need ...

Verified Answer:

Since

\Pi

= MRT, the...

Question: 11.9

CALCULATING VAPOR-PRESSURE LOWERING How many grams of sucrose must be added to 320 g of water to lower the vapor pressure by 1.5 mm Hg at 25°C? The vapor pressure of water at 25 °C is 23.8 mm Hg, and the molar mass of sucrose is 342.3 g/mol. STRATEGY According to Raoult’s law, Psoln = Psolv × Xsolv ...

Verified Answer:

First, calculate the vapor pressure of the solutio...

Question: 11.12

CALCULATING THE OSMOTIC PRESSURE OF A SOLUTION The total concentration of dissolved particles inside red blood cells and in the surrounding plasma is approximately 0.30 M, and the membrane surrounding the cells is semipermeable. What would the maximum osmotic pressure in atmospheres inside the ...

Verified Answer:

\Pi

=

\left(0.30 \frac{mol}...

Question: 11.13

USING OSMOTIC PRESSURE TO CALCULATE THE MOLARITY OF A SOLUTION A solution of an unknown substance in water at 293 K gives rise to an osmotic pressure of 5.66 atm. What is the molarity of the solution? STRATEGY We are given values for Π and T , and we need to solve for M in the equation Π = MRT. ...

Verified Answer:

M =

\frac{5.66 atm}{\left(0.082 06 \frac{...

Question: 11.7

USING HENRY’S LAW TO CALCULATE GAS SOLUBILITY The Henry’s-law constant of methyl bromide (CH3Br), a gas used as a soil fumigating agent, is k = 0.159 mol/(L · atm) at 25 °C. What is the solubility in mol/L of methyl bromide in water at 25 °C and a partial pressure of 125 mm Hg? STRATEGY According ...

Verified Answer:

k = 0.159 mol/(L · atm) P = 125 mm Hg ×

\fr...

Question: 11.8

CALCULATING THE VAPOR PRESSURE OF A SOLUTION What is the vapor pressure in mm Hg of a solution made by dissolving 18.3 g of NaCl in 500.0 g of H2O at 70 °C, assuming a van’t Hoff factor of 1.9? The vapor pressure of pure water at 70 °C is 233.7 mm Hg. STRATEGY According to Raoult’s law, the vapor ...

Verified Answer:

First, use molar mass to calculate the number of m...

Question: 11.10

INTERPRETING VAPOR PRESSURE CURVES The following diagram shows a close-up view of part of the vapor-pressure curves for two pure liquids and a mixture of the two. Which curves represent pure liquids, and which represents the mixture? ...

Verified Answer:

The vapor pressure of a mixture of two volatile li...

Question: 11.6

USING DENSITY TO CONVERT MOLARITY TO OTHER MEASURES OF CONCENTRATION A 0.750 M solution of H2SO4 in water has a density of 1.046 g/mL at 20 °C. What is the concentration of this solution in (a) mole fraction, (b) mass percent, and (c) molality? The molar mass of H2SO4 is 98.1 g/mol. ...

Verified Answer:

(a) Let’s pick an arbitrary amount of the solution...

Question: 11.5

USING DENSITY TO CONVERT FROM MOLALITY TO MOLARITY Ethylene glycol, C2H4(OH)2, is a colorless liquid used as automobile antifreeze. If the density at 20 °C of a 4.028 m solution of ethylene glycol in water is 1.0241 g/mL, what is the molarity of the solution? The molar mass of ethylene glycol is ...

Verified Answer:

The mass of the solution is the sum of the masses ...

Question: 11.4

CALCULATING THE MOLALITY OF A SOLUTION What is the molality of a solution made by dissolving 1.45 g of table sugar (sucrose, C12H22O11) in 30.0 mL of water? The molar mass of sucrose is 342.3 g/mol. STRATEGY Molality is the number of moles of solute per kilogram of solvent. Thus, we need to find ...

Verified Answer:

The number of moles of sucrose is 1.45 g sucrose ×...