Polarity & Electronegativity
Intermolecular Forces & Solubility Rules
Saturation
Aqueous solutions & Colligative Properties
Miscellaneous
100
The degree of polarity of a chemical bond in a molecule of a compound can be predicted by determining the difference in the
A) melting points of the elements in the compound
B) densities of the elements in the compound
C) electronegativities of the bonded atoms in a molecule of the compound
D) atomic masses of the bonded atoms in a molecule of the compound
C) electronegativities of the bonded atoms in a molecule of the compound
100
Double Jeopardy :)
A student adds solid KCl to water in a flask. The flask is sealed with a stopper and thoroughly shaken until no more solid KCl dissolves. Some solid KCl is still visible in the flask. The solution in the flask is
A) saturated and is at equilibrium with the solid KCl
B) saturated and is not at equilibrium with the solid KCl
C) unsaturated and is at equilibrium with the solid KCl
D) unsaturated and is not at equilibrium with the solid KCl
No more solid KCl dissolves = saturated
solid KCl at the bottom is at equilibrium with aq KCl dissolved in water
A) saturated and is at equilibrium with the solid KCl
100
How many grams of KCl must be dissolved in 100 grams of water to make a saturated solution at 60°C?
45 g
100
As a solute is added to a solvent, what happens to the freezing point and the boiling point of the solution?
A) The freezing point decreases and the boiling point decreases.
B) The freezing point decreases and the boiling point increases.
C) The freezing point increases and the boiling point decreases.
D) The freezing point increases and the boiling point increases.
B) The freezing point decreases and the boiling point increases.
100
Double Jeopardy!
Ethane, C2H6, has a boiling point of -89°C at standard pressure. Ethanol, C2H5OH, has a much higher boiling point than ethane at standard pressure. At STP, ethane is a gas and ethanol is a liquid.
Compare the intermolecular forces of the two substances at STP.
Possible answers:
— Ethane has weaker intermolecular forces (IMF) than ethanol.
–Ethanol has hydrogen bonding
200
Electronegativity is a measure of an atom's ability to
A) attract the electrons in the bond between the atom and another atom
B) repel the electrons in the bond between the atom and another atom
C) attract the protons of another atom
D) repel the protons of another atom
A) attract the electrons in the bond between the atom and another atom
200
Double Jeopardy! :)
Which substance has the strongest hydrogen bonding?
A) PH3
B) NH3
C) CH4
D) H2Se
B) NH3
H of one molecule attracts a N, O, or F of another molecule
200
An unsaturated solution is formed when 80. grams of a salt is dissolved in 100. grams of water at 40.°C. This salt could be
A) KCl
B) KNO3
C) NaCl
D) NaNO3
Saturation for NaNO3 at 40.°C is 105 g
80 g is less than 105 g = unsaturated
D) NaNO3
200
Calcium oxide, CaO, also known as lime, is an important industrial chemical. Lime can be obtained by the heating of limestone, which is mainly calcium carbonate, CaCO3.
CaCO3(s) + heat --> CaO(s) + CO2(g)
State the solubility of limestone in water.
CaCO3 has very low solubility.
200
Which statement describes a solution of sodium chloride in water?
A) The mixture is heterogeneous, the solute is NaCl and the solvent is H2O.
B) The mixture is heterogeneous, the solute is H2O and the solvent is NaCl.
C) The mixture is homogeneous, the solute is NaCl and the solvent is H2O.
D) The mixture is homogeneous, the solute is H2O and the solvent is NaCl.
C) The mixture is homogeneous, the solute is NaCl and the solvent is H2O.
300
The chemical bond between which two atoms is most
polar?
A) C–N
B) H–H
C) S–Cl
D) Si–O
C - N
2.6 3.0 Difference = 0.4
H - H Diff = 0
S - Cl
2.6 3.2 Diff = 0.6
Si - O
1.9 3.4 Diff = 1.5
300
stronger intermolecular attractions
300
A solution is formed by dissolving 45 grams of NH4Cl in 100 grams of H2O at 70ºC. Which statement correctly describes this solution?
A) NH4Cl is the solute, and the solution is saturated.
B) NH4Cl is the solute, and the solution is unsaturated.
C) NH4Cl is the solvent, and the solution is saturated.
D) NH4Cl is the solvent, and the solution is unsaturated
NH4Cl = solute
water = solvent
unsaturated b/c saturation is at ~62 g. We currently have 45 g so less than 62 g
B) NH4Cl is the solute, and the solution is unsaturated.
300
Compared to a 0.1 M aqueous solution of NaCl, a 0.8 M aqueous solution of NaCl has a
_________ boiling point ___________ freezing point
HIGHER BP; LOWER FP
b/c more solutes are in the solution (0.1 --> 0.8 M)
so harder for water molecules to change from liquid to gas
300
Which type of bonding is usually exhibited when the electronegativity difference between two atoms is 1.1?
1.1 is between 0.4 and 1.7
polar covalent
400
Polar molecule = Asymmetrical charge distribution
D)
400
Natural gas is a mixture that includes butane, ethane, methane, and propane. Differences in boiling points can be used to separate the components of natural gas. The boiling points at standard pressure for these components are listed in the table below.
List the four components of natural gas in order of increasing strength of intermolecular forces.
Lowest BP = weakest IMF
methane --> ethane --> propane --> butane
weakest strongest
400
What is the mass of NH4Cl that must dissolve in 200. grams of water at 50.°C to make a saturated solution?
At 100 g of water: 53 g NH4Cl
At 200 g of water: 53 * 2 = 106 g
or if 52 g, then 104 g
Range = +/- 2
400
Lowest freezing point = most solutes
meaning HIGHEST concentration = 0.1 M
400
CO2 is a solute that can dissolve in water.
a) Identify whether this solute is ionic or covalent
b) How many solute particles will this result when dissolved in water?
Covalent
1!
500
At STP, which of these substances is most soluble in H2O?
A) CCl4
B) CO2
C) HCl
D) N2
C) HCl
H2O is polar;
polar substances dissolves in polar substances
Answer: C) HCl = polar molecule
500
Based on Table F, which equation represents a saturated solution having the lowest concentration of Cl– ions?
A) NaCl(s) <--> Na+(aq) + Cl–(aq)
B) AgCl(s) <--> Ag+(aq) + Cl–(aq)
C) NH4Cl(s) <--> NH4+(aq) + Cl–(aq)
D) KCl(s) <--> K+(aq) + Cl–(aq)
B) AgCl(s) <--> Ag+(aq) + Cl–(aq)
AgCl does not dissolve in water = insoluble
so it should have the lowest concentration of Cl ions in the water
500
When 21 grams of KCl are dissolved in 50. grams of water at 25°C, the resulting mixture can be described as
A) heterogeneous and unsaturated
B) heterogeneous and supersaturated
C) homogeneous and unsaturated
D) homogeneous and supersaturated
at 100 g water: KCl saturated at 35 g
at 50 g water: KCl saturated at 35/2 = 17.5 g
We have 21 grams, which is GREATER than 17.5 g
supersaturated & heterogeneous!
500
An aqueous solution of MgCl2 has a higher boiling point than an aqueous solution of _________
A) FeCl3
B) CaCl2
C) BaCl2
D) NaCl
MgCl2 has 3 solute particles dissolved
We are looking for less solute particles so MgCl2 has a higher boiling point
D) NaCl = 2 solute particles
500
A saturated solution of sulfur dioxide is prepared by dissolving SO2(g) in 100. g of water at 10.°C and standard pressure.
Based on Table G, state the general relationship between solubility and temperature of an aqueous SO2 solution at standard pressure.
Possible answers include:
— The solubility increases as the temperature decreases.
— As the temperature of the solution increases, the solubility of SO2 decreases.
— At lower temperatures, more SO2 can dissolve.