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Chapter 28: Q23P (page 792)

Barium titanate, a ceramic used in electronics, was analyzed by the following procedure: Into a Pt crucible was placed \(1.2\;{\rm{g}}\)of \({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3}\) and \(0.8\;{\rm{g}}\)of \({\rm{N}}{{\rm{a}}_2}\;{{\rm{B}}_4}{{\rm{O}}_7}\)plus \(0.3146\;{\rm{g}}\)of unknown. After fusion at \({1000^\circ }{\rm{C}}\)in a furnace for\(30\;{\rm{min}}\), the cooled solid was extracted with \(50\;{\rm{mL}}\)of\(6{\rm{MHCl}}\), transferred to a \(100 - {\rm{mL}}\) volumetric flask, and diluted to the mark. A \(25.00 - {\rm{mL}}\)aliquot was treated with \(5\;{\rm{mL}}\)of \(15\% \)tartaric acid (which complexes \({\rm{T}}{{\rm{i}}^{4 + }}\)and keeps it in aqueous solution) and \(25\;{\rm{mL}}\)of ammonia buffer,\({\rm{pH}}9.5\). The solution was treated with organic reagents that complex\({\rm{B}}{{\rm{a}}^{2 + }}\), and the \({\rm{Ba}}\)complex was extracted into \({\rm{CC}}{{\rm{l}}_4}.\)After acidification (to release the \({\rm{B}}{{\rm{a}}^{2 + }}\) from its organic complex), the \({\rm{B}}{{\rm{a}}^{2 + }}\)was backextracted into\(0.1{\rm{MHCl}}\). The final aqueous sample was treated with ammonia buffer and methylthymol blue (a metal ion indicator) and titrated with \(32.49\;{\rm{mL}}\) of \(0.01144{\rm{M}}\)EDTA. Find the weight per cent of Ba in the ceramic.

Short Answer

Expert verified

The weight percent of Ba in the ceramic is \(0.6049\)%.

Step by step solution

01

Defining the weight percent.

The Weight Percentage is simply the ratio of a solute's mass to the mass of a solution multiplied by 100. The Weight Percentage is also referred to as the Mass Percentage.

\(Percent by weight = \frac{{{\rm{ gram of solute }}}}{{100g{\rm{ of solution }}}}\)

02

Determining the moles of EDTA and \({\rm{B}}{{\rm{a}}^{2 + }}\).

Here \(1/4\)of the sample is required for EDTA titration so we will first calculate the moles of EDTA spent on titration:

\(n({\rm{EDTA}}) = c \times V\)

\(n({\rm{EDTA}}) = 0.01144{\rm{M}} \times (0.03249\;{\rm{L}})\)

\(n({\rm{EDTA}}) = 3.717 \times {10^{ - 4}}\;{\rm{mol}}\)

Next we will determine the moles of \({\rm{B}}{{\rm{a}}^{2 + }}\)and calculate its mass:

\(n\left( {{\rm{B}}{{\rm{a}}^{2 + }}} \right) = 4 \times n({\rm{ EDTA }})\)

\(n\left( {{\rm{B}}{{\rm{a}}^{2 + }}} \right) = 4 \times 3.717 \times {10^{ - 4}}\;{\rm{mol}} = 1.487 \times {10^{ - 3}}\;{\rm{mol}}\)

\( \to m\left( {{\rm{B}}{{\rm{a}}^{2 + }}} \right) = 0.2042\;{\rm{g}}\)

03

Determining the weight percent.

Now calculating the weight percent

\(wt\% = \frac{{m\left( {{\rm{B}}{{\rm{a}}^{2 + }}} \right)}}{{m({\rm{ unknown }})}}\)

\(wt\% = \frac{{0.2042\;{\rm{g}}}}{{0.3146\;{\rm{g}}}}\)

\(wt\% = 0.6049\)

Therefore the weight percent of Ba in the ceramic is \(0.6049\)%.

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Most popular questions from this chapter

Question: Consider a random mixture containing \(4.00\;{\rm{g}}\)of \({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3}\) (density\(2.532g/mL\)) and \(96.00\;{\rm{g}}\)of \({{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3}\) (density\(2.428\;{\rm{g}}/{\rm{mL}}\)) with a uniform spherical particle radius of\(0.075\;{\rm{mm}}\).

(a) Calculate the mass of a single particle of \({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3}\) and the number of particles of \({\rm{N}}{{\rm{a}}_2}{\rm{C}}{{\rm{O}}_3}\) in the mixture. Do the same for\({{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3}\).

(b) What is the expected number of particles in \(0.100\;{\rm{g}}\)of the mixture?

(c) Calculate the relative sampling standard deviation in the number of particles of each type in a \(0.100\;{\rm{g}}\)sample of the mixture.

To pre-concentrate cocaine and benzoylecgonine from river water described at the opening of this chapter, solid-phase extraction was carried out at \({\rm{pH}}\,\,2\) using the mixed-mode cation-exchange resin in Figure 28-19. After passing \(500\;{\rm{mL}}\)of river water through \(60{\rm{mg}}\)of resin, the retained analytes were eluted first with \(2\;{\rm{mL}}\)of \({\rm{C}}{{\rm{H}}_3}{\rm{OH}}\)and then with \(2\;\,\,{\rm{mL }}of\,\,\,2\% \) ammonia solution in\({\rm{C}}{{\rm{H}}_3}{\rm{OH}}\). Explain the purpose of using \({\rm{pH}}2\) for retention and dilute ammonia for elution.

To pre-concentrate cocaine and benzoylecgonine from river water described at the opening of thischapter, solid-phase extraction was carried out at2mL pH2using the mixed-mode cationexchange resin in Figure 28-19. After passing 500mLof river water through  60mgof resin, the retained analytes were eluted first with2mLof localid="1663594337127" CH3OHand then with localid="1663594104084" 2mLof2% ammonia solution inCH3OH. Explain the purpose of using pH2for retention and dilute ammonia for elution.

(a) Explain how dispersive liquid-liquid microextraction reduces the use of solvent in comparison with liquid-liquid extraction.

(b) What is the purpose of the disperser solvent, which is used in much greater volume than the extraction solvent?

Acid-base equilibria of Cr(III) were summarized in Problem 10-36. Cr(VI) in aqueous solution above pH 6 exists as the yellow tetrahedral chromate ion, \({\rm{CrO}}_4^{2 - }.\)Between\({\rm{pH}}2\)and \(6,{\rm{Cr}}\)(VI) exists as an equilibrium mixture of\({\rm{HCrO}}_4^ - \) and orange-red dichromate,\({\rm{C}}{{\rm{r}}_2}{\rm{O}}_7^{2 - }.{\rm{Cr}}({\rm{VI}})\) is a carcinogen, but \({\rm{Cr }}(III)\)is not considered to be as harmful. The following procedure was used to measure\({\rm{Cr }}({\rm{VI}})\) in airborne particulate matter in workplaces.

1. Particles were collected by drawing a known volume of air through a polyvinyl chloride filter with \(5 - \mu {\rm{M}}\)pore size.

2. The filter was placed in a centrifuge tube and \(10\;{\rm{mL}}\)of \(0.05{\rm{M}}{\left( {{\rm{N}}{{\rm{H}}_4}} \right)_2}{\rm{S}}{{\rm{O}}_4}/0.05{\rm{MN}}{{\rm{H}}_3}buffer,{\rm{pH}}8,\) were added. The immersed filter was agitated by ultrasonic vibration for\(30\;{\rm{min}}\)at \({35^\circ }{\rm{C}}\)to extract all \({\rm{Cr }}(III)and{\rm{Cr}}\)(VI) into solution.

3. A measured volume of extract was passed through a "strongly basic" anion exchanger (Table 26-1) in the \({\rm{C}}{{\rm{l}}^ - }\)form. Then the resin was washed with distilled water. Liquid containing \({\rm{Cr}}\)(III) from the extract and the wash was discarded.

4. Cr(VI) was then eluted from the column with\(0.5{\rm{M}}{\left( {{\rm{N}}{{\rm{H}}_4}} \right)_2}{\rm{S}}{{\rm{O}}_4}/0.05{\rm{MN}}{{\rm{H}}_3}\) buffer, \({\rm{pH}}8,\)and collected in a vial.

5. The eluted \({\rm{Cr}}\)(VI) solution was acidified with \({\rm{HCl}}\)and treated with a solution of 1,5 -diphenylcarbazide, a reagent that forms a colored complex with Cr(VI). The concentration of the complex was measured by its visible absorbance.

(a) What are the dominant species of \({\rm{Cr}}\)(VI) and \({\rm{Cr}}\)(III) at\({\rm{pH}}8\)?

(b) What is the purpose of the anion exchanger in step 3 ?

(c) Why is a "strongly basic" anion exchanger used instead of a "weakly basic" exchanger?

(d) Why is Cr(VI) eluted in step 4 but not step 3 ?
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