University of Puerto Rico
Rio Piedras Campus
Natural Sciences Faculty
Department of Chemistry
CRES program
General Chemistry 3002
Review Test 1
I. Intermolecular forces
Definitions:
a.
b.
c.
d.
Intermolecular forces: are nonbonding forces. Forces between particles.
Cohesive forces: intermolecular forces that occur within a liquid.
Adhesive forces: intermolecular forces that occur between the liquid and the tube.
Viscosity: Resistance to flow
Tipos de Fuerzas Intermoleculares:
a. London: Are present in all substances.
b. Dipole-dipole induced: are present in mixtures. It has to be a mixture between a
polar molecule and another with only London forces.
c. Ion-dipole induced: are present in mixtures. It has to be a mixture between an ionic
compound and another compound whose only intermolecular force is the London
force.
d. Dipole-Dipole: occur between molecules having an intrinsic dipole moment, that
generally can relate to a difference in electronegativity.
e. Hydrogen bonds: when no links are present between H and F, H and O, H and N.
f. Ion Dipole: ions of a substance may interact with polar molecules of the polar
covalent. Thus, the negative pole of one molecule attracts the positive ion and
positive polo interacts with the negative ion: parts of each molecule are joined by
forces of attraction of opposite charges.
Important Trends:
a.
b.
c.
d.
e.
f.
At higher temperature, higher pressure
Low intermolecular forces, higher vapor pressure
Increased external pressure, higher boiling point
Mayor dipole moment, Mayor dipole-dipole forces
Mayor intermolecular forces, Mayor boiling point
High molar mass, greater dispersion forces, greater energy for separating the
particles, higher tension surface.
g. Increased intermolecular forces, Low slip tendencies liquid particles will, High
viscosity.
h. Higher vapor pressure, less polarizable
i. The more branched, less london forces
Ejercicios de Practica:
1. Ordered in descending order according to the priority for intermolecular forces.
2. Which have higher boiling between, HCl and HF? Explain
3. Determine which intermolecular forces are present in the following:
a. Kr
b. NCl3
c. H2S
d. NH3
e. N2
f. C3H6O
g. CCl4
4. Order in ascending orders boiling point. Explains
CH3CH3
CH3CH2Cl
CH4
CH3CH2OH
5. Between each pair chosen who have the highest boiling point. explains
a. CH3OH or
CH3SH
b. CH3OCH3
or
CH3CH2OH
c. NH3
or
CH4
6. Choose who have the highest vapor pressure at a given temperature.
a. Br2
ó
I2
b. C3H8O
ó
CH4O
c. H2S
ó
H2O
7. ¿ Which will have higher surface tension, or H2O CH3COCH3?
8. ¿ Which have increased viscosity? explains
9. If a sample of 55.0 mL of water is heated to the boiling point. How much additional
heat is required to evaporate the sample? (Assume water density 1.00 g/mL) Hevap
=40.7 kJ/mol.
10. How much heat, in kJ, is required to heat a 10.0g of ice at -7 oC to water vapor at
125 oC?Cice = 2.09 J/g oC, Cwater = 4.18 J/g oC, Cvapor = 2.01 J/g oC,
evap = 40.7 kJ/mol, = 6.017 kJ/mol.
11. Consider the following phase diagram and answer the following questions for iodine.
a. ¿What is the normal boiling point of iodine?
b. ¿What is the melting point at 1 atm?
c. ¿Which phase is present at room temperature and normal atmospheric pressure?
d. ¿What phase is present at 186 oC and 1.0 atm?
e. ¿What state change happens in an isothermal process at 185 0C from 0.1 atm to
100 atm?
II. Solutions 2
Useful Information:
a.
b.
c.
d.
e.
f.
g.
h. Hsoln = Hsolute+ Hsolvente+ Hmezclar
i. Hhidrat = Hsolvente + Hmezclar
j. Gsoln = Hsoln – T Ssoln
k. Sgas = kH x Pgas
Definitions:
a. Solution: a homogeneous mixture. Its particles are atoms, ions or small molecules
(diameter <3.10 mm). Example. NaCl
b. Colloid: A heterogeneous mixture. Their particles are macromolecules - protein,
polysaccharide, nucleic acid - molecules or small aggregates that do not settle
(diameter 10.3 - 1 mm). Example: milk
c. Suspension: It's a heterogeneous mixture. Its particles can be seen with the eyes
because they are larger and settle over time (diameter> 1 mm). Example: sand in
water.
d. Homogeneous Mixture: are those in which the blend components are not
identifiable to the simple eye.
e. Heterogeneous Mixture: is one that has a non-uniform composition which can be
distinguished at first sight his component and is formed by two or more substances
different physically distributed unevenly.
f. Miscible: mixing and therefore dissolves.
g. Solubility: is the maximum amount of solute dissolved in an amount of solvent at a
given temperature.
h. : is the change in enthalpy when a solution is formed from the solute and solvent.
i. : is the change in entropy (molecular disorder) when a solution is formed from the
solute and solvent.
j. Exothermic dissolution: container is heated when dissolution occurs. Hsoluto +
Hsolvente < Hmezclar .
Hsoln < 0
k. Endothermic dissolution: container is cooled when dissolution occurs. Hsoluto +
Hsolvente > Hmezclar .
Hsoln > 0
l. Solvation: process in where the solute is surrounded by solvent.
m. Hydration: process wherein the water is surrounded by solute. Hhidrat relates the ion
charge density
n. Supersaturated solution: one that contains more than the maximum amount of
solute dissolved at a given temperature.
o. Unsaturated solution: one that does not contain the maximum amount of solute
dissolved at a given temperature.
Ejercicios:
1. The partial pressure of carbon dioxide in a soda can is 4 atm at 250 oC. ¿ What is
-2
CO2 solubility? K = 3.3 x10 mol/L*atm.
2. An aqueous solution of 16.00% by mass of glycerol, C3H5(OH)3, has a density of
1.037g/mL. ¿ What will be the molarity, mole fraction and molarity for C3H5(OH)3?
3. A sample of 11.3 mL of ethanol (CH 3 OH) (d = 0.796 g / mL) is dissolved in
sufficient water to make 75.0 mL of a solution with density 0.980 g / mL. ¿ What is
the concentration expressed as molar fraction of water, molarity of ethanol and
ethanol molality?
4. Determine which of the following is soluble in hexane and explains:
a) water
b) propane (CH3CH2CH3),
c) ammonia (NH3),
d) hydrochloric acid (HCl)
5. ¿Which is more soluble in water, CCl4 or CH2Cl2? Explains
6. Indicates which of the following compounds are more soluble in water or hexane.
Explains
a. Glucose
b. Naphthalene
c. Dimethyl Ether CH3OCH3
d. Toluene
7. When NH4Cl dissolved in water, the solution becomes cold. ¿The dissolution is
endothermic or exothermic? ¿What does that mean?
8. If a person prepares a fishbowl using water previously boiled and cooled, to put the
fish, it will die. Explain.
9. ¿What will be the final volume that should be have a solution which will have
dissolved 50.0 mL of a 5.00 M KI solution, so that 25.0 mL of the diluted solution
containing 3.25 g of KI?
10. A solution prepared by dissolving 28.4 g of glucose (C6H12O6) in 355 g of water has
a final volume of 378 mL solution. For this solution, calculate the following:
molarity, molality, percent by mass and mole fraction for glucose.
III.Colligative Properties
Definitions:
a. Colligative Properties: Colligative properties are those which depend of the
number of solute particles and no of the chemical identity of the solute.
Example. Reduced vapor pressure, increased boiling point, reduction in
the freezing point, osmotic pressure.
b. Electrolyte: substance that when dissolved in water produce a solution that
conducts electricity.
c. Osmosis: process in which a solvent flows through a semipermeable
membrane from a dilute solution to a concentrated one.
d. Semipermeable Membrane: material that allows passage of the solvent but
not the solute.
e. Osmotic Pressure: pressure required to prevent the net movement of solvent
through a semipermeable membrane.
Formulas:
a. Reduced steam pressure
P = P°solvente – Psolvente = i Xsoluto P°solvente
b. Increased boiling point
Tb = Tb soln – Tb solvente = i Kb m
c. Reduction in freezing point
Tf = Tf solvente – Tf soln = i Kf m
d. Osmotic Pressure
= iMRT
i = numbers of ions in the formula unit
Non-Volatile and Non-Electrolytes (i = 1)
Volatile and Non-Electrolytes (i = 1)
Strong electrolytes (i > 1)
Phase diagram: