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EXAMPLE- Particles designated \(50/00\)mesh pass through a 50 mesh sieve bou are retained by a lo0 mesh sieve. Their size is in the range 0.150-0.300 mm.

does not pass is retained for your sample. This procedure gives particles whose diameters are in the range \(0.85 - 1.18\;{\rm{mm}}.\) We refer to the size range as \(16/20{\rm{mesh}}.\)

Suppose that much finer particles of \(80/120\)mesh size (average diameter \( = 152\mu {\rm{m}},\) average volume\( = 1.84\;{\rm{nL}}\)) were used instead. Now the mass containing \({10^4}\) particles is reduced from \(11.0to0.0388\;{\rm{g}}.\) We could analyze a larger sample to reduce the sampling uncertainty for chloride.

Short Answer

Expert verified

The mass of the mesh particle that reduces the \({\rm{KCl}}\)to a \(1\% \)uncertainty is \(0.61{\rm{ }}g.\)

Step by step solution

01

Concept used

The mass of the mesh particle that reduces the \({\rm{KCl}}\)to a \(1\% \)uncertainty must be computed.

In sampling n number of particles, the standard deviation is given as

\({S_{\rm{n}}} = \sqrt {{\rm{npq}}} \)

Where,

The chance of drawing B type particles is\({\rm{q}}\)

02

Step 2:

Solution:

The mass of the mesh particle that reduces the KCl to a\({\rm{1\% }}{\rm{.}}\)uncertainty.

\(1\% \)of\({\rm{KCl}}\)particle has the same standard deviation as \(1\% \) of np.

\({\sigma _{\rm{n}}} = \sqrt {{\rm{npq}}} \)

\({\rm{p}} = 0.01{\rm{q}} = 0.99\)we get \({\rm{n}} = 9.9 \times {10^5}particles\)

Using conventional sieves, the particle diameter is estimated.

Suitable for 170/200 mesh

\( = \frac{{0.090\;{\rm{mm}}(170{\rm{ sievenumber }}) + 0.075\;{\rm{mm}}(200{\rm{ sievenumber }})}}{2} = 0.0825\;{\rm{mm}}\)

\(\frac{4}{3}\pi {(0.0825\;{\rm{mm}})^3} = 2.35 \times {10^{ - 3}}\;{\rm{mL}}\)is used to compute the particle volume.

The mass of 1% chloride is computed as follows:

\(Mass = \left( {9.9 \times {{10}^5}} \right.particle)\left( {0.00236 \times \times {{10}^{ - 6}}\;{\rm{mL}}/} \right.particle)(2.108\;{\rm{g}}/{\rm{mL}}) = 0.61\;{\rm{g}}\)

Conclusion

The mass of the mesh particle that reduces the \({\rm{KCl}}\)to a\({\rm{1\% }}\)uncertainty was computed.

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Most popular questions from this chapter

From their standard reduction potentials, which of the following metals would you expect to dissolve in \({\rm{HCl}}\)by the reaction\({\rm{M}} + n{{\rm{H}}^ + } \to {{\rm{M}}^{n + }} + \frac{n}{2}{{\rm{H}}_2}:{\rm{Zn}},{\rm{Fe}},{\rm{Co}},{\rm{Al}},{\rm{Hg}},{\rm{Cu}},{\rm{Pt}}\),\({\bf{Au}}\)?

(When the potential predicts that the element will not dissolve, it probably will not. If it is expected to dissolve, it may dissolve if some other process does not interfere. Predictions based on standard reduction potentials at \({\bf{2}}{{\bf{5}}^{^{\bf{o}}}}C\) are only tentative, because the potentials and activities in hot, concentrated solutions vary widely from those in the table of standard potentials.)

In 2002, workers at the Swedish National Food Administration discovered that heated, carbohydrate-rich foods, such as french fries, potato chips, and bread, contain alarming levels \((0.1to4\mu {\rm{g}}/{\rm{g}})\) of acrylamide, a known carcinogen\(36\).

After the discovery, simplified methods were developed to measure ppm levels of acrylamide in food. In one procedure,\(10\;{\rm{g}}\) of pulverized, frozen french fries were mixed for \(20\;{\rm{min}}\)with\(50\;{\rm{mL}}\) of \({{\rm{H}}_2}{\rm{O}}\)to extract acrylamide, which is very soluble in water \((216\;{\rm{g}}/100\;{\rm{mL}}).\)The liquid was decanted and centrifuged to remove suspended matter. The internal standard \(^2{{\rm{H}}_3}\)-acrylamide was added to\(1\;{\rm{mL}}\) of extract. A solid-phase extraction column containing \(100{\rm{mg}}\)of cation-exchange polymer with protonated sulfonic acid groups\(\left( { - {\rm{S}}{{\rm{O}}_3}{\rm{H}}} \right.)\) was washed twice with 1 -mL portions of methanol and twice with \(1 - {\rm{mL}}\)portions of water. The aqueous food extract \((1{\rm{mL}})\)was then passed through the column to bind protonated acrylamide \(\left( { - {\rm{NH}}_3^ + } \right)\)to sulfonate \(\left( { - {\rm{SO}}_3^ - } \right)on\)the column. The column was dried for\(30\;{\rm{s }}at\)\(0.3\)bar and then acrylamide was eluted with\(1\;{\rm{mL}}\) of \({{\rm{H}}_2}{\rm{O}}.\)Eluate was analyzed by liquid chromatography with a polar bonded phase. The chromatograms show the results moni- tored by ultraviolet absorbance or by mass spectrometry. The retention time of acrylamide is different on the two columns because they have different dimensions and different flow rates.

(a) What is the purpose of solid-phase extraction prior to chromatography? How does the ion-exchange sorbent retain acrylamide?

(b) Why are there many peaks when chromatography is monitored by ultraviolet absorbance?

(c) Mass spectral detection used selected reaction monitoring (Figure 22-33) with the \(m/z72 \to 55\)transition for acrylamide and \(75 \to 58fo{r^2}{{\rm{H}}_3}\)-acrylamide. Explain how this detection method works and suggest structures for the ions with \({\rm{m}}/{\rm{z}}72\)and 55 from acrylamide.

(d) Why does mass spectral detection give just one major peak?

(e) How is the internal standard used for quantitation with mass spectral detection?

(f) Where does \(^2{{\rm{H}}_3}\)-acrylamide appear with ultraviolet absorbance? With mass spectral selected reaction monitoring?

(g) Why does the mass spectral method give quantitative results even though retention of acrylamide by the ion-exchange sorbent is not quantitative and elution of acrylamide from the sorbent by \(1\;{\rm{mL}}\) of water might not be quantitative?

Chromatograms of acrylamide extract after passage through solid-phase extraction column. Left: Phenomenex Synergi Polar-RP 4- \(\mu {\rm{m}}\)column eluted with 96:4 \((vol/vol){{\rm{H}}_2}{\rm{O}}:{\rm{C}}{{\rm{H}}_3}{\rm{CN}}.\)Right: Phenomenex Synergi Hydro-RP 4- \(\mu {\rm{m}}\)column eluted with \(96:4:0.1(vol/vol/vol){{\rm{H}}_2}{\rm{O}}:{\rm{C}}{{\rm{H}}_3}{\rm{OH}}:{\rm{HC}}{{\rm{O}}_2}{\rm{H}}.\) (Data from L. Peng. T. Farkas, L. Loo, \({\rm{J}}.\)Teuscher, and \({\rm{K}}.\)Kallury, "Rapid and Reproducible Extraction of Acrylamide in French Fries Using a Single Solid-Phase Sorbent," Am. Lab. News Ed, October 2003, p. 10.)

Referring to Table 28-7, explain how an anion-exchange resin can be used for absorption and analysis of \({\bf{S}}{{\bf{O}}_2}\)released by combustion.

What mass of sample in Figure 28-3 is expected to give a sampling standard deviation of \( \pm 6\% \)?

How many 2.8-g samples must be analyzed to give 95% confidence that the mean is known to within ±4%?

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