A.P. Chemistry
Chapter 10 – 13 Review
1. A student performs an experiment to determine the volume of hydrogen gas produced when a
given mass of magnesium reacts with excess HCl(aq). The student begins with a 0.0360 g sample
of pure magnesium and a solution of 2.0 M HCl(aq).
a. Write the net ionic equation for the reaction between magnesium metal and
hydrochloric acid
b. Calculate the number of moles of magnesium in the 0.0360 g sample
c. Calculate the number of moles of HCl(aq) needed to completely react with the sample
of magnesium.
As the magnesium reacts, the hydrogen gas produced is collected by water displacement at
23.00C. The pressure of the gas in the collection tube is measured to be 749 torr.
d. Given that the equilibrium vapor pressure of water is 21 torr at 23.00C, calculate the
pressure that the H2 gas produced in the reaction would have if it were dry.
e. Calculate the volume, in liters, measured at the conditions in the laboratory, that the
H2(g) produced in the reaction would have if it were dry.
f.
The laboratory procedure specified that the concentration of the HCl solution be 2.0 M,
but only 12.3 M HCl solution was available. Describe the steps for safely preparing 50.0
mL of 2.0 M HCl(aq) using 12.3 M HCl solution and materials selected from the list
below. Show any necessary calculation(s).
10.0 mL graduated cylinder
Distilled water
250 mL beakers
Balance
50.00 mL volumetric flask
Dropper
2. Answer the following questions in terms of principles of chemical bonding and intermolecular
forces. In each explanation where a comparison is to be made, a complete answer must include
a discussion of both substances. Consider the following molecules:
a. At 1 atm and 298 K, pentane is a liquid whereas propane is a gas. Explain.
b. At 1 atm and 298 K, methanol is a liquid whereas propane is a gas. Explain.
c. Indicate the hybridization of the carbon atom in each of the following:
i. Methanol
ii. Methanoic (formic) acid
d. Draw the complete Lewis electron-dot diagram for a molecule of propanoic acid,
C3H5OOH.
e. Explain the following observations about the two carbon-oxygen bonds in the
methanoate (formate) anion, HCO2-, You may draw a Lewis electron-dot diagram (or
diagrams) of the methanoate ion as part of your explanations.
i. The two carbon-oxygen bonds in the methanoate (formate) anion, HCO2-, have
the same length.
ii. The length of the carbon-oxygen bonds in the methanoate (formate) anion,
HCO2-, is intermediate between the length of the carbon-oxygen bond in
methanol and the length of the carbon-oxygen bond in methanal.
A.P. Chemistry
Chapter 10 – 13 Review
Answers
1. A student performs an experiment to determine the volume of hydrogen gas produced when a
given mass of magnesium reacts with excess HCl(aq). The student begins with a 0.0360 g sample
of pure magnesium and a solution of 2.0 M HCl(aq).
a. Write the net ionic equation for the reaction between magnesium metal and
hydrochloric acid
Mg(s) + 2 H+(aq)  Mg2+(aq) + H2(g)
b. Calculate the number of moles of magnesium in the 0.0360 g sample
1 𝑚𝑜𝑙 𝑀𝑔
0.0360 g Mg x 24.31 𝑔 𝑀𝑔 = 0.00148 mol Mg
c. Calculate the number of moles of HCl(aq) needed to completely react with the sample
of magnesium.
2 𝑚𝑜𝑙 𝐻 +
0.00148 mol Mg x 1 𝑚𝑜𝑙 𝑀𝑔 = 0.00296 mol HCl
As the magnesium reacts, the hydrogen gas produced is collected by water displacement at
23.00C. The pressure of the gas in the collection tube is measured to be 749 torr.
d. Given that the equilibrium vapor pressure of water is 21 torr at 23.00C, calculate the
pressure that the H2 gas produced in the reaction would have if it were dry.
P(H2) = P(tot) – P(H2O) = 749 torr – 21 torr = 728 torr
e. Calculate the volume, in liters, measured at the conditions in the laboratory, that the
H2(g) produced in the reaction would have if it were dry.
PV = nRT
V=
𝑛𝑅𝑇
𝑃
f.
=
1 𝑎𝑡𝑚
728 torr x 760 𝑡𝑜𝑟𝑟 = 0.958 atm = P
(𝑜.𝑜𝑜148 𝑚𝑜𝑙 𝐻2 )(0.0821
0.958 𝑎𝑡𝑚
𝐿 𝑎𝑡𝑚
)(296 𝐾)
𝑚𝑜𝑙 𝐾
= 0.0375 L
The laboratory procedure specified that the concentration of the HCl solution be 2.0 M,
but only 12.3 M HCl solution was available. Describe the steps for safely preparing 50.0
mL of 2.0 M HCl(aq) using 12.3 M HCl solution and materials selected from the list
below. Show any necessary calculation(s).
10.0 mL graduated cylinder
Distilled water
250 mL beakers
Balance
50.00 mL volumetric flask
Dropper
M1V1 = M2V2 (12.3 M)V1 = (2.0 M)(50.0 mL)
V1 = 8.1 mL
Pour some distilled water into a 50.00 mL volumetric flask so that it is about half full. Use
the graduated cylinder to measure 8.1 mL of the concentrated HCl then add that slowly to
the volumetric flask and swirl to mix. Add more distilled water and fill to the line with the
dropper. Cap and shake 13x’s.
Answer the following questions in terms of principles of chemical bonding and intermolecular forces. In each
explanation where a comparison is to be made, a complete answer must include a discussion of both
substances. Consider the following molecules:
a. At 1 atm and 298 K, pentane is a liquid whereas propane is a gas. Explain.
Pentane has more ldf than propane because pentane has more electrons than propane. The higher
ldf means a stronger attraction, which leads to a higher boiling point.
b. At 1 atm and 298 K, methanol is a liquid whereas propane is a gas. Explain.
Propane molecules only have ldf, while methanol has ldf and hydrogen-bonding. Hydrogen bonding
is a stronger intermolecular attraction than ldf alone, which leads to stronger intermolecular forces
between the methanol molecules than the propane molecules. The stronger the imf, the higher the
boiling point, which is why methanol is a liquid, while propane is a gas.
c. Indicate the hybridization of the carbon atom in each of the following:
i. Methanol
sp3
ii. Methanoic (formic) acid
sp3
d. Draw the complete Lewis electron-dot diagram for a molecule of propanoic acid, C3H5OOH.
e. Explain the following observations about the two carbon-oxygen bonds in the methanoate
(formate) anion, HCO2-, You may draw a Lewis electron-dot diagram (or diagrams) of the
methanoate ion as part of your explanations.
i.
The two carbon-oxygen bonds in the methanoate (formate) anion, HCO2-, have
the same length.
There are 2 resonance structures, one for each oxygen having a single bond and the
other a double bond. The average would be a 1.5 bond.
ii.
The length of the carbon-oxygen bonds in the methanoate (formate) anion, HCO2-,
is intermediate between the length of the carbon-oxygen bond in methanol and
the length of the carbon-oxygen bond in methanal.
Since the average of the resonance structures is a 1.5 bond, the bond length of
methanoate would be halfway between the single bond of methanol and the double
bond of methanol.