3/23/25, 7:20
AM
CHEM 210 MIDTERM 2 EXAM QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS
Terms in this set (63)
The equivalence point of a titration is reached
when the moles of titrant added are
stoichiometrically equal to the moles of analyte
present in solution. This is
Identify the equivalence observed on the titration curve as the point in the
point on the titration center of the steepest part of the curve, which
curve. correlates to the greatest concentration (pH) change
Define the end point of a per volume of added titrant for the titration.
titration. The equivalence point of a titration is the
theoretical result of a titration, but what is actually
measured is the end point. The end point is when a
sudden change occurs in a physical property of the
analyte solution
that implies equivalence or thereabouts. A common
example is the color change of an indicator.
In the Fajans titration of Negative
Hg2+2Hg22+, NaClNaCl is
added to produce the In the Fajans titration of Hg2+2 with NaCl, the solution
precipitate contains excess Hg2+2 before the equivalence point.
Hg2Cl2Hg2Cl2. The end The excess Hg2+2 adsorbs onto the surface of the
point of the titration is precipitate, imparting a positive charge onto the
detected with precipitate. After the equivalence point, there is
bromophenol blue. excess Cl−Cl− in solution, which adsorbs to the
What charge do you surface of the precipitate, imparting a negative
expect the precipitate to charge onto the precipitate.
have after the equivalence
point?
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,3/23/25, 7:20
AM
In the Volhard method, a known excess of standard
AgNO3AgNO3 is added to the CN−CN− in 0.5 M
HNO3HNO3 solution while stirring vigorously,
resulting in the precipitation of AgCNAgCN.
Ag+(aq)+CN−
(aq)⟶AgCN(s)Ag+(aq)+CN−(aq)⟶AgCN(s)
Vigorous stirring is required to prevent excess Ag+Ag+
from becoming trapped in the precipitate as it forms.
The next step is to filter off the AgCNAgCN
precipitate and wash it with dilute HNO3HNO3. This
step is required because AgCNAgCN is more soluble
than AgSCNAgSCN, which is formed later in the
titration. If AgCNAgCN is not removed from the
solution, the end point will slowly fade as AgCNAgCN
Describe how the redissolves and is replaced by AgSCNAgSCN. After
Volhard method can be the precipitate is removed, Fe(NO3)3Fe(NO3)3
used to solution is added to the filtrate to give a
determine the CN−CN− concentration of 0.2 M Fe3+Fe3+. The excess Ag+Ag+
concentration of a in the filtrate is then titrated with a standard
solution by placing the KSCNKSCN solution.
steps in the order they
occur. Ag+(aq)+SCN−
(aq)⟶AgSCN(s)Ag+(aq)+SCN−(aq)⟶AgSCN(s)
Once all of the Ag+Ag+ has been consumed,
SCN−SCN− reacts with Fe3+Fe3+ to form a red
complex, which signifies the end point of the back
titration.
Fe3+(aq)+SCN−(aq)⟶FeSCN2+
(aq)Fe3+(aq)+SCN−(aq)⟶FeSCN2+(aq)
The amount of SCN−SCN− required for the back
titration tells you the excess amount of Ag+Ag+ from
the reaction with CN−CN−. Because the total amount
2/19
, 3/23/25, 7:20
AM
of Ag+Ag+ added to the solution is known, the amount that reacted with CN−CN− can be determined.
3/19
AM
CHEM 210 MIDTERM 2 EXAM QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS
Terms in this set (63)
The equivalence point of a titration is reached
when the moles of titrant added are
stoichiometrically equal to the moles of analyte
present in solution. This is
Identify the equivalence observed on the titration curve as the point in the
point on the titration center of the steepest part of the curve, which
curve. correlates to the greatest concentration (pH) change
Define the end point of a per volume of added titrant for the titration.
titration. The equivalence point of a titration is the
theoretical result of a titration, but what is actually
measured is the end point. The end point is when a
sudden change occurs in a physical property of the
analyte solution
that implies equivalence or thereabouts. A common
example is the color change of an indicator.
In the Fajans titration of Negative
Hg2+2Hg22+, NaClNaCl is
added to produce the In the Fajans titration of Hg2+2 with NaCl, the solution
precipitate contains excess Hg2+2 before the equivalence point.
Hg2Cl2Hg2Cl2. The end The excess Hg2+2 adsorbs onto the surface of the
point of the titration is precipitate, imparting a positive charge onto the
detected with precipitate. After the equivalence point, there is
bromophenol blue. excess Cl−Cl− in solution, which adsorbs to the
What charge do you surface of the precipitate, imparting a negative
expect the precipitate to charge onto the precipitate.
have after the equivalence
point?
1/19
,3/23/25, 7:20
AM
In the Volhard method, a known excess of standard
AgNO3AgNO3 is added to the CN−CN− in 0.5 M
HNO3HNO3 solution while stirring vigorously,
resulting in the precipitation of AgCNAgCN.
Ag+(aq)+CN−
(aq)⟶AgCN(s)Ag+(aq)+CN−(aq)⟶AgCN(s)
Vigorous stirring is required to prevent excess Ag+Ag+
from becoming trapped in the precipitate as it forms.
The next step is to filter off the AgCNAgCN
precipitate and wash it with dilute HNO3HNO3. This
step is required because AgCNAgCN is more soluble
than AgSCNAgSCN, which is formed later in the
titration. If AgCNAgCN is not removed from the
solution, the end point will slowly fade as AgCNAgCN
Describe how the redissolves and is replaced by AgSCNAgSCN. After
Volhard method can be the precipitate is removed, Fe(NO3)3Fe(NO3)3
used to solution is added to the filtrate to give a
determine the CN−CN− concentration of 0.2 M Fe3+Fe3+. The excess Ag+Ag+
concentration of a in the filtrate is then titrated with a standard
solution by placing the KSCNKSCN solution.
steps in the order they
occur. Ag+(aq)+SCN−
(aq)⟶AgSCN(s)Ag+(aq)+SCN−(aq)⟶AgSCN(s)
Once all of the Ag+Ag+ has been consumed,
SCN−SCN− reacts with Fe3+Fe3+ to form a red
complex, which signifies the end point of the back
titration.
Fe3+(aq)+SCN−(aq)⟶FeSCN2+
(aq)Fe3+(aq)+SCN−(aq)⟶FeSCN2+(aq)
The amount of SCN−SCN− required for the back
titration tells you the excess amount of Ag+Ag+ from
the reaction with CN−CN−. Because the total amount
2/19
, 3/23/25, 7:20
AM
of Ag+Ag+ added to the solution is known, the amount that reacted with CN−CN− can be determined.
3/19
