Department of Chemistry
UNIVERSITY OF CAPE TOWN
PRIVATE BAG
RONDEBOSCH 7701 SOUTH AFRICA
CEM1000W - TUTORIAL 11: 2019
Question 1
(i)
Which solute is more soluble in the given solvent? Explain your choice.
a. 1-Butanol (CH3CH2CH2CH2OH) or 1,4-butanediol (HOCH2CH2CH2CH2OH) in water
b. Chloroform (CHCℓ3) or carbon tetrachloride (CCℓ4) in water
(ii)
In which solvent is the solute most soluble? Explain your choice.
a. Sodium chloride in methanol (CH3OH) or in propanol (CH3CH2CH2OH)
b. Ethylene glycol (HOCH2CH2OH) in hexane (CH3CH2CH2CH2CH2CH3) or in water
Question 2
Water is added to a flask containing solid NH4Cl. As the salt dissolves, the solution becomes colder.
(i)
Is the dissolving of NH4Cl exothermic or endothermic?
(ii)
Is the magnitude of ∆Hlattice of NH4Cl larger or smaller than the combined ∆Hhydr of the ions? Explain.
(iii)
Given the answer to (ii), why does NH4Cl dissolve in water?
Question 3
After opening a 200 mL bottle of fizzy drink at standard temperature and pressure and letting it go
completely ‘flat’, 0.50 L of CO2 gas are released. Prior to opening the bottle, what was the pressure of CO2
inside the bottle? Henry’s law constant for CO2 in water is 3.3 × 10-2 mol∙L-1∙atm-1
Question 4
Salt when added to water can act as antifreeze by lowering the freezing point of the salt solution formed.
(i)
Calculate the mass of salt to be added to water to create a solution with freezing point -3.3 °C. Kb =
0.512 °C∙m-1 , Kf = 1.86 °C∙m-1, water density = 0.997 g∙ml-1, the volume of pure solvent is 0.997 L
and assume it remains unchanged on addition of salt.
(ii)
Ethylene glycol is a much more commonly used antifreeze than salt implying that salt is not fit for
purpose, why might this be the case? Explain.
Question 5
Complete the following table and calculate the decrease in the freezing point of water when 1 mol glycerol
(CH2OH-CHOH-CH2OH), NaCl or Na2CO3 is dissolved in 1.00 kg of water. (Kf for water is 1.858 °C m-1)
Moles compound
Glycerol
NaCl
Na2CO3
1.00
1.00
1.00
Moles solute particles
Molality (mol kg-1)
∆Tf
Freezing point of
water in solution
Which solution would have the highest boiling point? ___________
Question 6
The osmotic pressure of human blood is 7.65 atm at 37 °C. What mass of glucose, C6H12O6, is required to
make 1.00 L of aqueous solution for intravenous feeding if the solution must have the same osmotic
pressure as blood at body temperature, 37 °C?
Question 7
(i) What specific fact about a physical property of a solution must be true to call it a colligative property?
(ii) At 21°C a solution of 18.26 g of a non-volatile, nonpolar compound in 33.25 g of liquid ethyl bromide,
C2H5Br had a vapour pressure of 336.0 torr. The vapour pressure of pure ethyl bromide at this temperature
is 400.0 torr. Calculate: the mole fractions of solute and solvent, the number of moles of solute present and
the molecular mass of the solute.
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Minimal Formula sheet
q = n Csubstance,phase ΔT
q = n ΔHphase change
View Molecules in 3D
http://bit.ly/2YeUFqV