CHEM 101L QUESTIONS AND ANSWERS
If the balanced equation for the reaction of magnesium hydroxide with hydrochloric acid is: 2 HCl (aq) + Mg(OH)2 (s) —►MgCl2 (aq) +2 H2O (l) How many moles of MgCl2 can be produced when an antacid containing 6.750x102 mg of magnesium hydroxide is completely ne...
CHEM 101L QUESTIONS AND ANSWERS
If the balanced equation for the reaction of magnesium hydroxide with
hydrochloric acid is: 2 HCl (aq) + Mg(OH)2 (s) —►MgCl2 (aq) +2 H2O (l) How
many moles of MgCl2 can be produced when an antacid containing 6.750x102 mg
of magnesium hydroxide is completely neutralized by HCl? (Mg(OH)2 MW =
58.3197 g/mol)
0.01157 mol
An antacid sample contains 0.0350 moles of magnesium hydroxide. 0.0500 moles
of hydrochloric acid are added. Which chemical species would you expect to
encounter in excess in solution after mixing?
Reaction Equation: Mg(OH)2 + 2 HCl →2 H2O + MgCl2
Mg2+, HO-, Cl-
A tablet containing 1500 mg calcium carbonate should neutralize more acid than
a tablet containing 1125 mg calcium carbonate and 225 mg magnesium hydroxide
because __________________.
A. There are more mg of active ingredient.
B. There are more moles of base.
C. None of these is true. The tablet containing 1500 mg calcium carbonate will
react with fewer moles of acid.
D. Each magnesium hydroxide reacts with more moles of acid.
E. Each calcium carbonate reacts with more moles of acid.
C. None of these is true. The tablet containing 1500 mg calcium carbonate will react
with fewer moles of acid.
After mixing 0.0500 moles HCl with 0.0350 moles of magnesium hydroxide in a
crushed antacid sample, the pH after mixing was measured initially as 3.4, then
increased and stabilized after 2-3 minutes at a value of 4.1. A well-reasoned
explanation for this result would be:
A. None of these explains the behavior. Clearly the experiment was not performed
correctly and cannot be interpreted.
B. Based solely on the number of moles added, there should be excess acid, and
a pH less than 7. Thus, the results are consistent with experimental expectations.
C. Based solely on the number of moles added, there should be excess base, and
a pH greater than 7. However, because the solubility of magnesium hydroxide is
low, it is possible that not all moles of base were in solution, and a slowly rising
pH could be caused as more base dissolves.
D. Based solely on the number of moles added, there should be excess base, and
a pH less than 7. Thus, the results are consistent with experimental expectations.
E. Based solely on the number of moles added, there should be excess acid, and
a pH greater than 7. However, because the solubility of magnesium hydroxide is
low, it is possible that not all moles of base were in solution, and a slowly rising
pH could be caused as more base dissolves.
Feedback
Based solely on the number of moles added, there should be excess base, and a pH
greater than 7. However, because the solubility of magnesium hydroxide is low, it is
, possible that not all moles of base were in solution, and a slowly rising pH could be
caused as more base dissolves.
In the reaction NaOH(s) + HCl (aq) → NaCl(aq) + H2O(l), the spectator ion(s) would
be:
Cl-
To carry out Experiment 6 quantitatively, one major adjustment was made to the
procedure followed in Experiment 2. That adjustment was:
Select one:
A. None of these is true.
B. The thermometers were calibrated to give accurate temperature readings in °C.
C. Calculations were made in moles rather than in grams.
D. All solutions were equilibrated to room temperature before beginning the
experiment.
E. The calorimeter was calibrated to account for heat loss from the system.
The calorimeter was calibrated to account for heat loss from the system.
In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be: (Select
all that apply.)
Select one:
A. -(qsoln + qcal)
B. qcal -qsoln
C. qsoln -qcal
D. ΔH / nreagent
E. the heat gained or lost by the reaction in units of joules.
F. the heat gained or lost by the reaction in units of joules/mol.
G. the difference between the extrapolated maxiumum temperature and the initial
temperature in a reaction.
H. qsoln + qcal
I. Both A and E are true.
J. Both D and F are true.
I. Both A and E are true.
In a calorimetry experiment, 50.0 mL each of two dilute aqueous solutions are
combined and produce an extrapolated T = 22.4˚C. If the density of each solution
is assumed to be equal to that of water (at 20˚C, d = 0.9982 g/mL), and the specific
heat of the solution is also equal to that of water (4.186 J/g˚C), the value of qrxn
would be:
-9.38 kJ
In a conductivity titration, 10.15 mL of 4.95 x 10-3 M Ba(OH)2 is titrated by a 4.15 x
10-3 M H2SO4 solution. The end point of the titration would be expected at a
volume of:
12.11 mL
A conductivity plot for the titration of barium hydroxide with sulfuric acid is
shown below. Assuming sulfuric acid is the titrant, which ion species would you
expect to be significant in solution when 11.62 mL of titrant had been added?
A. Ba2+
B. SO42-
C. H+
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