Analytical Chemistry Board Exam Practice Flashcards

Flashcards based on the October 2019 Chemists Licensure Examination in Analytical Chemistry (Set A).

What is the molality of $37.0\text{ wt \%}$ $\text{HCl}$ with a density of $1.19\,g/mL$?

$$16.1\,m$$

When a solution containing one mole of sodium carbonate ($\text{Na}_2\text{CO}_3$) and a solution containing one mole of sulfuric acid ($\text{H}_2\text{SO}_4$) are mixed, what products are formed?

One mole of sodium sulfate ($\text{Na}_2\text{SO}_4$) and one mole of carbonic acid ($\text{H}_2\text{CO}_3$)

What is the safest method for performing a flame test in the laboratory?

Soak a wooden splint in an aqueous solution of the metal salt, then burn the splint in the flame from a Bunsen burner.

What is the chemical formula and formula mass of the mineral trona?

Formula: $\text{Na}_2\text{CO}_3 \cdot \text{NaHCO}_3 \cdot 2\text{H}_2\text{O}$, Formula mass: $226\,g\,mol^{-1}$

Which statistical test should be used to determine if outdoor sunlight exposure significantly alters plastic samples compared to indoor lab control samples?

F-test followed by a two-sample T-test

Which statistical test is used to compare whether the mean results of lead ($\text{Pb}$) analysis from two independent laboratories differ significantly?

T-test

What sources of error can occur during the sample preparation stage of analytical measurements?

Loss of sample during weighing or dissolution, contamination by impurities in reagents or environment, mass changes from varying humidity and temperature, and obtaining an inhomogeneous sample from the bulk.

How is the overall standard deviation ($s_{overall}$) calculated from sampling standard deviation ($s_s$) and analytical procedure standard deviation ($s_a$)?

$s_{overall} = \sqrt{s_s^2 + s_a^2}$ (for $s_s = \pm 4\%$ and $s_a = \pm 3\%$, $s_{overall} = \pm 5\%$).

What instrumental performance characteristic is usually desired for an analytical method?

High signal-to-noise ratio

How should a hydronium ion concentration be reported for a pH reading of $3.45$ using correct significant figures?

$3.5 \times 10^{-4}\,M$ (the two decimal places in pH dictate two significant figures).

Under what conditions is it best to use external standards for calibration of instrument response?

When there are no interference effects from matrix components in the analyte solution, and when analyzing a large number of samples with uniform composition.

What is the best method to decrease random uncertainty in acid-base titration measurements?

Replicate the analysis.

Which titration method uses dichlorofluorescein indicator and dextrin for determining chloride content using silver nitrate?

Fajan's method

What core assumption is made in least squares linear regression analysis?

Errors in X values are insignificant relative to errors in measured Y values.

What half-reaction change occurs at the anode of an electrochemical cell?

Oxidation, such as $2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-$

What is the correct charge balance equation for an aqueous solution of $\text{H}_2\text{SO}_4$ that ionizes to $\text{HSO}_4^-$ and $\text{SO}_4^{2-}$?

$$[\text{H}^+] = [\text{OH}^-] + [\text{HSO}_4^-] + 2[\text{SO}_4^{2-}]$$

According to Le Chatelier's principle, why does $\text{Al(OH)}_4^- + 3e^- \rightleftharpoons \text{Al}(s) + 4\text{OH}^-$ become a stronger reducing agent in more basic solutions?

Increasing $[\text{OH}^-]$ favors the reverse oxidation reaction, making $\text{Al}(s)$ a stronger reducing agent.

How does complexation with cyanide ($\text{CN}^-$) affect the stability of $\text{Fe(III)}$ compared to $\text{Fe(II)}$?

$\text{Fe(III)}$ is more stabilized by complexation with $\text{CN}^-$ than $\text{Fe(II)}$.

Why is manganese(II) sulfide ($\text{MnS}$) most soluble in an aqueous solution of $1\,M\,\text{HCl}$?

Protons ($\text{H}^+$) react with sulfide ions ($\text{S}^{2-}$) to form weak acid $\text{H}_2\text{S}$, driving the dissolution equilibrium forward.

Which chromatographic technique is most suitable for analyzing high molecular weight compounds soluble in non-polar solvents?

Gel permeation chromatography

In what order should $\text{NaCl}$, $\text{Na}_2\text{SO}_4$, and $\text{Na}_2\text{S}$ be added to sequentially precipitate $\text{Ag}^+$, $\text{Ba}^{2+}$, and $\text{Ni}^{2+}$ separately?

First $\text{NaCl}$ (precipitates $\text{AgCl}$), second $\text{Na}_2\text{SO}_4$ (precipitates $\text{BaSO}_4$), and third $\text{Na}_2\text{S}$ (precipitates $\text{NiS}$).

What three transport mechanisms move dissolved species to and from an electrode surface?

Diffusion, Migration, and Convection.

How is alkalinity defined in natural water analysis?

Alkalinity is the capacity of natural water to react with $\text{H}^+$ to reach pH $4.5$ (the second equivalence point of carbonate), caused mainly by $\text{OH}^-$, $\text{CO}_3^{2-}$, and $\text{HCO}_3^-$.

Match the EDTA titration curves shown in the figure to their corresponding metal ions: $\text{Ca}^{2+}$, $\text{Cu}^{2+}$, $\text{Fe}^{3+}$, $\text{Mg}^{2+}$.

Plot I corresponds to $\text{Fe}^{3+}$, Plot II to $\text{Cu}^{2+}$, Plot III to $\text{Ca}^{2+}$, and Plot IV to $\text{Mg}^{2+}$.

Which organic precipitating agent is used specifically for the gravimetric precipitation of nickel in alkaline solution?

Dimethylglyoxime (DMG)

Which component is common to GC systems but NOT HPLC systems?

Gaseous mobile phase (carrier gas), whereas HPLC uses liquid mobile phase (eluent).

How are transmittance ($T$) and absorbance ($A$) defined in spectrophotometry?

$T = \frac{I}{I_0}$ and $A = -\log_{10}(T) = \log_{10}\left(\frac{I_0}{I}\right)$

How do the energy and frequency of violet light ($400\,nm$) compare to red light ($750\,nm$)?

Violet light has a shorter wavelength, higher frequency, and higher energy than red light.

Which chromatographic detector has relatively low sensitivity compared to flame ionization or electron capture detectors?

Thermal Conductivity Detector (TCD)

Which analytical techniques can simultaneously provide quantitative, species, structural, and spatial distribution information?

Mass spectrometry and Nuclear Magnetic Resonance (NMR) spectrometry

Which isotopes can be analyzed using Nuclear Magnetic Resonance (NMR) spectroscopy?

Isotopes with non-zero nuclear spin, such as $^{13}\text{C}$, $^{15}\text{N}$, and $^{19}\text{F}$.

In Beer's Law ($A = \epsilon b c$), what physical quantity corresponds to the slope of a plot of absorbance ($A$) versus concentration ($c$)?

The product of molar absorptivity ($\epsilon$) and path length ($b$).

In Atomic Absorption Spectroscopy (AAS) of mercury, which pair of intensities is used to determine mercury concentration?

$I(615.2\,nm)$ (intensity from lamp) and $I_d(615.2\,nm)$ (intensity at detector).

Why does fluorescence (emission) spectroscopy offer higher sensitivity than absorption spectroscopy?

Fluorescence intensity is measured against a zero background, and emitted light is at a longer wavelength than absorbed light.

In Gas Chromatography (GC), what analyte properties govern separation?

Boiling point, molecular weight, and polarity.

In mass spectrometry, which species generate peaks on the mass spectrum when a molecular ion $M^{+\bullet}$ fragments?

Only charged species generate peaks ($M^{+\bullet}$, $A^+$, and $B^+$).

What is the most effective method to distinguish between two enantiomers?

Place one enantiomer in solution and pass plane-polarized light through it to measure optical rotation.

When hexanoic acid ($\text{RCO}_2\text{H}$) and 1-aminohexane ($\text{RNH}_2$) adjusted to pH 2 with $\text{HCl}$ are passed through a cation-exchange column ($\text{Na}^+$ form), which compound is retained?

Protonated 1-aminohexane ($\text{RNH}_3^+$) is retained because it is cationic at pH 2.

How is the wavelength of light altered when passing through a medium with refractive index $n$?

The wavelength in the medium is $\lambda = \frac{\lambda_0}{n}$ (e.g. $589\,nm$ in honey with $n = 1.50$ becomes $393\,nm$).

Based on the excitation and emission spectra for compound Y, which excitation and emission wavelengths yield maximum fluorescence intensity?

Excitation wavelength $\lambda_{ex} = 315\,nm$ and emission wavelength $\lambda_{em} = 415\,nm$.