Chapter 9, Complexometric Reactions and Titrations Video Solutions, Analytical Chemistry

00:18

Problem 1

Distinguish between a complexing agent and a chelating agent.

Carlene Jimenez

Numerade Educator

03:31

Problem 2

Explain the principles of chelation titration indicators.

Nicholas White

Numerade Educator

04:25

Problem 3

Why is a small amount of magnesium salt added to the EDTA solution used for the titration of calcium with an Eriochrome Black T indicator?

Vishal Sharma

Numerade Educator

02:00

Calcium ion forms a weak 1: 1 complex with nitrate ion with a formation constant of $2.0 .$ What would be the equilibrium concentrations of $\mathrm{Ca}^{2+}$ and $\mathrm{Ca}\left(\mathrm{NO}_{3}\right)^{+}$ in a solution prepared by adding $10 \mathrm{~mL}$ cach of $0.010 \mathrm{M} \mathrm{CaCl}_{2}$ and $2.0 \mathrm{M}$ NaNO $_{3}$ ? Neglect diverse ion effects.

Lottie Adams

Numerade Educator

00:22

Problem 5

The formation constant of the silver-ethylenediamine complex, $\mathrm{Ag}\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)^{+},$ is $5.0 \times 10^{4} .$ Calculate the concentration of $\mathrm{Ag}^{+}$ in
equilibrium with a $0.10 \mathrm{M}$ solution of the complex. (Assume no higher order complexes.)

Sisi Gao

Numerade Educator

04:00

Problem 6

What would be the concentration of $\mathrm{Ag}^{+}$ in Problem 5 if the solution contained also $0.10 \mathrm{M}$ ethylenediamine, $\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2} ?$

Ronald Prasad

Numerade Educator

03:29

Problem 7

Silver ion forms stepwise complexes with thiosulfate ion, $\mathrm{S}_{2} \mathrm{O}_{3}{ }^{2-},$ with $K_{n}=6.6 \times 10^{8}$ and $K_{f 2}=4.4 \times 10^{4} .$ Calculate the equilibrium concentrations of all silver species for $0.0100 \mathrm{M} \mathrm{AgNO}_{3}$ in $1.00 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$. Neglect diverse
ion effects.

David Collins

Numerade Educator

02:43

Problem 8

The formation constant for the lead-EDTA chelate $\left(\mathrm{Pb} \mathrm{Y}^{2-}\right)$ is $1.10 \times 10^{18}$ Calculate the conditional formation constant (a) at $\mathrm{pH} 3$ and $(\mathrm{b})$ at $\mathrm{pH} 10 .$

Aadit Sharma

Numerade Educator

04:35

Problem 9

Using the conditional constants calculated in Problem 8 calculate the $\mathrm{pPb}$ $\left(-\log \left[\mathrm{Pb}^{2+}\right]\right)$ for $50.0 \mathrm{~mL}$ of a solution of $0.0250 \mathrm{M} \mathrm{Pb}^{2+}$ (a) at $\mathrm{pH} 3$ and
(b) at $\mathrm{pH} 10$ after the addition of (1) $0 \mathrm{~mL},$ (2) $50 \mathrm{~mL},$ (3) $125 \mathrm{~mL}$, and (4) $200 \mathrm{~mL}$ of $0.0100 \mathrm{M}$ EDTA.

Anthony Han

Numerade Educator

02:43

Problem 10

The conditional formation constant for the calcium-EDTA chelate was calculated for pH 10 in Example 9.4 to be $1.8 \times 10^{10} .$ Calculate the conditional formation constant at $\mathrm{pH}$ 3. Compare this with that calculated for lead at $\mathrm{pH} 3$ in Problem $8 .$ Could lead be titrated with EDTA at $\mathrm{pH} 3$ in the presence of calcium?

Aadit Sharma

Numerade Educator

01:41

Problem 11

Calculate the weight of $\mathrm{Na}_{2} \mathrm{H}_{2} \mathrm{Y} \cdot 2 \mathrm{H}_{2} \mathrm{O}$ required to prepare $500.0 \mathrm{~mL}$ of $0.05000 \mathrm{M}$ EDTA.

James Irizarry

Numerade Educator

06:30

Problem 12

An EDTA solution is standardized against high-purity $\mathrm{CaCO}_{3}$ by dissolving $0.3982 \mathrm{~g} \mathrm{CaCO}_{3}$ in hydrochloric acid, adjusting the $\mathrm{pH}$ to 10 with ammoniacal buffer, and titrating. If $38.26 \mathrm{~mL}$ was required for the titration, what is the molarity of the EDTA?

Susan Hallstrom

Numerade Educator

01:45

Problem 13

Calculate the titer of $0.1000 \mathrm{M}$ EDTA in $\mathrm{mg} \mathrm{CaCO}_{3} / \mathrm{mL}$

David Collins

Numerade Educator

01:45

Problem 14

If $100.0 \mathrm{~mL}$ of a water sample is titrated with $0.01000 \mathrm{M}$ EDTA, what is the titer of the EDTA in terms of water hardness/mL?

David Collins

Numerade Educator

08:16

Problem 15

Calcium in powdered milk is determined by ashing a $1.50-\mathrm{g}$ sample and then titrating the calcium with EDTA solution, $12.1 \mathrm{~mL}$ being required. The EDTA was standardized by titrating $10.0 \mathrm{~mL}$ of a zinc solution prepared by dissolving 0.632 g zinc metal in acid and diluting to $1 \mathrm{~L}(10.8 \mathrm{~mL}$. EDTA required for titration). What is the conccntration of calcium in the powdered milk in parts per million?

Yongyao Zhou

Numerade Educator

01:45

Problem 16

Calcium is determined in serum by microtitration with EDTA. A $100-\mu \mathrm{L}$ sample is treated with two drops of $2 \mathrm{M} \mathrm{KOH},$ Cal-Red indicator is added, and the titration is performed with $0.00122 \mathrm{M}$ EDTA, using a microburet. If $0.203 \mathrm{~mL}$ EDTA is required for titration, what is the level of calcium in the serum in $\mathrm{mg} / \mathrm{dL}$ and in meq/L?

David Collins

Numerade Educator

02:59

Problem 17

In the Liebig titration of cyanide ion, a soluble complex is formed; and at the equivalence point, solid silver cyanide is formed, signaling the end point.
$\begin{aligned} 2 \mathrm{CN}^{-}+\mathrm{Ag}^{+} & \rightarrow \mathrm{Ag}(\mathrm{CN})_{2}^{-} \quad \text { (titration) } \\ \mathrm{Ag}(\mathrm{CN})_{2}^{-}+\mathrm{Ag}^{+} \rightarrow \mathrm{Ag}\left[\mathrm{Ag}(\mathrm{CN})_{2}\right] & \text { (end point) } \end{aligned}$
A 0.4723-g sample of KCN was titrated with $0.1025 \mathrm{M} \mathrm{AgNO}_{3}$, requiring $34.95 \mathrm{~mL}$. What is the percent purity of the $\mathrm{KCN} ?$

Susan Hallstrom

Numerade Educator

02:20

Problem 18

Copper in saltwater near the discharge of a sewage treatment plant is determined by first separating and concentrating it by solvent extraction of its dithizone chelate at $\mathrm{pH} 3$ into methylene chloride and then evaporating the solvent, ashing the chelate to destroy the organic portion, and titrating the copper with EDTA. Three $1-\mathrm{L}$ portions of the sample are each extracted with $25-\mathrm{mL}$ portions of methylene chloride, and the extracts are combined in a 100 -mL volumetric flask and diluted to volume. A $50-\mathrm{mL}$ aliquot is evaporated, ashed, and titrated. If the EDTA solution has a $\mathrm{CaCO}_{3}$ titer of $2.69 \mathrm{mg} / \mathrm{mL}$ and $2.67 \mathrm{~mL}$ is required for titration of the copper, what is the concentration of copper in the seawater in parts per million?

Himanshu Garg

Numerade Educator

01:09

Problem 19

Chloride in serum is determined by titration with $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2} ; 2 \mathrm{Cl}^{-}+\mathrm{Hg}^{2+} \rightleftharpoons$
$\mathrm{HgCl}_{2}$. The $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}$ is standardized by titrating $2.00 \mathrm{~mL}$ of a $0.0108 \mathrm{M} \mathrm{NaCl}$
solution, requiring $1.12 \mathrm{~mL}$ to reach the diphenylcarbazone end point. A 0.500 -mL scrum sample is treated with $3.50 \mathrm{~mL}$ water, $0.50 \mathrm{~mL} 10 \%$ sodium tungstate solution, and $0.50 \mathrm{~mL}$ of $0.33 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}$ solution to precipitate proteins. After the proteins are precipitated, the sample is filtered through a dry filter into a dry flask. A $2.00-\mathrm{mL}$ aliquot of the filtrate is titrated with the $\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}$ solution, requiring $1.23 \mathrm{~mL}$. Calculate the meg/L chloride in the serum. (Note: mercury is rarely used today due to its toxicity. The problem is illustrative.)

David Collins

Numerade Educator

04:35

Problem 20

Prepare a spreadshcet for Figure $9.2, \log K_{f}^{\prime}$ vs. pH for the EDTA chelates of calcium. lcad, and mercury. This will require calculating $\alpha_{4}$ for EDTA and the $K_{f}$ values for the chelates of calcium, lead, and mercury, Calculate at $0.5 \mathrm{pH}$ intervals. Compare your plot with Figure 9.2

Anthony Han

Numerade Educator

29:26

Problem 21

Prepare a spreadshect for the titration of $100.00 \mathrm{~mL}$ of $0.1000 \mathrm{M} \mathrm{Ca}^{2+}$ with $0.1000 M$ NazEDTA at pH 10 (pCa vs. mL EDTA-Figure 9.3). Start out at $10 \mathrm{~mL}$ and then $20-\mathrm{mL}$ intervals of titrant, and gradually decrcase to $0.05 \mathrm{~mL}$ just before and after the cquivalue point. See Example 9.4

Teesta Dasgupta

University of Pittsburgh - Main Campus

04:35

Problem 22

Prepare a spreadsheet to plot the three $\beta$ values for $\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}{ }^{+}$ as a function of [NHy]. Plot from 0 to $0.01 M \mathrm{NH}_{3}$, beginning with increments of $0.0005 \mathrm{M}$, and after four intervals, use $0.001 \mathrm{M}$

Aadit Sharma

Numerade Educator

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