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Questions and Answers of Chemical Engineering

A cyanide ion-selective electrode obeys the equationE = constant - 0.059 16 log[CN-]The potential was - 0.230 V when the electrode was immersed in 1.00 mM NaCN.(a) Evaluate the constant in the
By how many volts will the potential of an ideal Mg2+ ion-selective electrode change if the electrode is removed from 1.00 × 10-4 M MgCl2 and placed in 1.00 × 10-3 M MgCl2 at 25°C?
When measured with a F- ion-selective electrode with a Nernstian response at 25°C, the potential due to F- in unfluoridated groundwater in Foxboro, Massachusetts, was 40.0 mV more positive than the
The selectivities of a Li+ ion-selective electrode are indicated on the following diagram. Which alkali metal (Group 1) ion causes the most interference? Which alkaline earth (Group 2) ion causes the
A metal ion buffer was prepared from 0.030 M ML and 0.020 M L, where ML is a metal ligand complex and L is free ligand. M + L ⇌ ML Kf = 4.0 × 108 Calculate the concentration of free metal ion,
The following data were obtained when a Ca2+ ion-selective electrode was immersed in standard solutions whose ionic strength was constant at 2.0 M.(a) Prepare a calibration curve and find the
The selectivity coefficient,KpotLi,H+, for a Li+ ion-selective electrode is 4 × 10-4. When this electrode is placed in 3.44 × 10-4 M Li solution at pH 7.2, the potential is - 0.333 V versus S.C.E.
From the following potentials, calculate the activity of Cl- in 1 M KCl.E°(calomel electrode) = 0.268 VE(calomel electrode, 1 M KCl) = 0.280 V
Standard addition. A particular CO2 compound electrode like the one in Figure 14-28 obeys the equation E = constant - [βRT (ln 10)/2F] log[CO2], where R is the gas constant, T is temperature (303.15
Ammonia in seawater was measured with an ammonia-selective electrode. A 100.0 mL aliquot of seawater was treated with 1.00 mL of 10 M NaOH to convert NH+4 to NH3. Therefore,V0 = 101.0 mL. A reading
Data below come from the graph in Box 14-2, for which the separate solutions method was used to measure selectivity coefficients for a sodium ion-selective electrode at 21.5°C. Use Equation 14-11 to
The H+ ion-selective electrode on the Phoenix Mars Lander has selectivity coefficients KpotHNA+ = 10-8.6 and KpotH+,Ca2+ = 10-7.8. Let A be the primary ion sensed by the electrode and let its charge
A Ca2+ ion-selective electrode was calibrated in metal ion buffers with ionic strength fixed at 0.50 M. Using the following electrode readings, write an equation for the response of the electrode to
The Pb2+ ion buffer used inside the electrode for the colored curve in Figure 14-27 was prepared by mixing 1.0 mL of 0.10 M Pb(NO3)2 with 100.0 mL of 0.050 M Na2EDTA. At the measured pH of 4.34,α
Solutions with a wide range of Hg2+ concentrations were prepared to calibrate an experimental Hg2+ ion-selective electrode. For the range 10 -5 < [Hg2+] [< 10-1 M, Hg(NO3)2 was used directly. The
Activity problem. Citric acid is a triprotic acid (H3A) whose anion (A3-) forms stable complexes with many metal ions.When a Ca2+ ion-selective electrode with a slope of 29.58 mV was immersed in a
What does analyte do to a chemical-sensing field effect transistor to produce a signal related to the activity of analyte?
For a silver-silver chloride electrode, the following potentials are observed:E° = 0.222 V E(saturated KCl) = 0.197 VFrom these potentials, find the activity of Cl- in saturated KCl. Calculate E for
A cell was prepared by dipping a Cu wire and a saturated calomel electrode into 0.10 M CuSO4 solution. The Cu wire was attached to the positive terminal of a potentiometer and the calomel electrode
Explain why a silver electrode can be an indicator electrode for Ag+ and for halides.
A 10.0-mL solution of 0.050 0 M AgNO3 was titrated with 0.025 0 M NaBr in the cellS.C.E. 7 || titration solution | Ag(s)Find the cell voltage for 0.1 and 30.0 mL of titrant.
A solution containing 50.0 mL of 0.100 M EDTA buffered to pH 10.00 was titrated with 50.0 mL of 0.020 0 M Hg(ClO4)2 in the cell shown in Exercise 14-B:S.C.E. 7 titration solution | Hg(l)From the cell
Consider the titration in Figure 15-2.(a) Write a balanced titration reaction.(b) Write two different half-reactions for the indicator electrode.(c) Write two different Nernst equations for the cell
Why don't Cr3+ and TiO2+ interfere in the analysis of Fe3+ when a Walden reductor, instead of a Jones reductor, is used for prereduction?
From information in Table 15-3, explain how you would use KMnO4 to find the content of (NH4)2S2O8 in a solid mixture with (NH4)2SO4. What is the purpose of phosphoric acid in the procedure?Table 15-3
Write balanced half-reactions in which MnO-4 acts as an oxidant at(a) pH = 0;(b) pH =10;(c) pH = 15.
When 25.00 mL of unknown were passed through a Jones reductor, molybdate ion (MoO2-4) was converted into Mo3+. The filtrate required 16.43 mL of 0.010 33 M KMnO4 to reach the purple end point.MnO-4 +
A 25.00-mL volume of commercial hydrogen peroxide solution was diluted to 250.0 mL in a volumetric flask. Then 25.00 mL of the diluted solution were mixed with 200 mL of water and 20 mL of 3 M H2SO4
Two possible reactions of MnO4 with H2O2 to produce O2 and Mn2 are(a) Complete the half-reactions for both schemes by adding e-, H2O, and H- and write a balanced net equation for each scheme.(b)
A 50.00-mL sample containing La3+ was treated with sodium oxalate to precipitate La2(C2O4)3, which was washed, dissolved in acid, and titrated with 18.04 mL of 0.006 363 M KMnO4. Calculate the
An aqueous glycerol solution weighing 100.0 mg was treated with 50.0 mL of 0.083 7 M Ce4+ in 4 M HClO4 at 60°C for 15 min to oxidize the glycerol to formic acid:The excess Ce4+ required 12.11 mL of
Nitrite (NO2-) can be determined by oxidation with excess Ce4+, followed by back titration of the unreacted Ce4+. A 4.030-g sample of solid containing only NaNO2 (FM 68.995) and NaNO3 was dissolved
Consider the titration of 100.0 mL of 0.010 0 M Ce4+ in 1 M HClO4 by 0.040 0 M Cu+ to give Ce3+ and Cu2+, using Pt and saturated Ag | AgCl electrodes to find the end point.(a) Write a balanced
Calcium fluorapatite (Ca10(PO4)6F2, FM 1 008.6) laser crystals were doped with chromium to improve their efficiency. It was suspected that the chromium could be in the +4 oxidation state.1. To
Primary-standard-grade arsenic(III) oxide (As4O6) is a useful (but carcinogenic) reagent for standardizing oxidants including MnO4- and I-3. To standardize MnO4-, As4O6 is dissolved in base and then
State two ways to make standard triiodide solution.
(a) Potassium iodate solution was prepared by dissolving 1.022 g of KIO3 (FM 214.00) in a 500-mL volumetric flask. Then 50.00 mL of the solution were pipetted into a flask and treated with excess KI
A 3.026-g portion of a copper(II) salt was dissolved in a 250-mL volumetric flask. A 50.0 mL aliquot was analyzed by adding 1 g of KI and titrating the liberated iodine with 23.33 mL of 0.046 68 M
H2S was measured by slowly adding 25.00 mL of aqueous H2S to 25.00 mL of acidified standard 0.010 44 M I-3 to precipitate elemental sulfur. (If [H2S] > 0.01 M, then precipitated sulfur traps some I-3
From the following reduction potentials(a) Calculate the equilibrium constant for .I2 (aq) + I- ‡Œ I-3 (b) Calculate the equilibrium constant for I2 (aq) + I- ‡Œ I-3 (c)
The Kjeldahl analysis in Section 10-8 is used to measure the nitrogen content of organic compounds, which are digested in boiling sulfuric acid to decompose to ammonia, which, in turn, is distilled
Consider the titration of 25.0 mL of 0.010 0 M Sn2+ by 0.050 0 M Tl3+ in 1 M HCl, using Pt and saturated calomel electrodes to find the end point.(a) Write a balanced titration reaction.(b) Write two
Some people have an allergic reaction to the food preservative sulfite (SO32-). Sulfite in wine was measured by the following procedure: To 50.0 mL of wine were added 5.00 mL of solution containing
Potassium bromate, KBrO3, is a primary standard for the generation of Br2 in acidic solution: BrO-3 + 5Br- + 6H+ ⇌ 3Br2 (aq) + 3H2O The Br2 can be used to analyze many unsaturated organic
Iodometric analysis of high-temperature superconductor. The procedure in Box 15-3 was carried out to find the effective copper oxidation state, and therefore the number of oxygen atoms, in the
Here is a description of an analytical procedure for superconductors containing unknown quantities of Cu(I), Cu(II), Cu(III), and peroxide (O22-):32 "The possible trivalent copper and/or
Li1 + y CoO2 is an anode for lithium batteries. Cobalt is present as a mixture of Co(III) and Co(II). Most preparations also contain inert lithium salts and moisture. To find the stoichiometry, Co
The oxidation numbers of Cu and Bi in high-temperature superconductors of the type Bi2Sr2(Ca0.8Y0.2)Cu2Ox (which could contain Cu2+, Cu3+, Bi3+, and Bi5+) can be measured by the following procedure.
Ascorbic acid (0.010 0 M) was added to 10.0 mL of 0.020 0 M Fe3+ in a solution buffered to pH 0.30, and the potential was monitored with Pt and saturated Ag | AgCl electrodes.Dehydroascorbic acid +
Select indicators from Table 15-2 that would be suitable for finding the end point in Figure 15-3. What color changes would be observed?Figure 15-3
Would tris(2,2 -bipyridine)iron be a useful indicator for the titration of Sn2+ with Mn(EDTA)-? (Hint: The potential at the equivalence point must be between the potentials for each redox couple.)
Explain what we mean by preoxidation and prereduction. Why is it important to be able to destroy the reagents used for these purposes?
Write balanced reactions for the destruction of S2O2-8 , Ag2+, and H2O2 by boiling.
The figure shows the behavior of Pt and Ag cathodes at which reduction of H3O+ to H2(g) occurs. Explain why the two curves are not superimposed.
What cathode potential (versus S.H.E.) is required to reduce 99.99% of Cd(II) from a solution containing 0.10M Cd(II) in 1.0 M ammonia if there is negligible current? Consider the following reactions
Electroplating efficiency. Nickel was electrolytically plated onto a carbon electrode from a bath containing 290 g/L NiSO4 ∙ 6H2O, 30 g/L B(OH)3, and 8 g/L NaCl at - 1.2 V vs. Ag | AgCl. The
Explain how the amperometric end-point detector in Figure 16-8 operates.Figure 16-8
The sensitivity of a coulometer is governed by the delivery of its minimum current for its minimum time. Suppose that 5 mA can be delivered for 0.1 s.(a) How many moles of electrons are delivered by
The experiment in Figure 16-8 required 5.32 mA for 964 s for complete reaction of a 5.00 mL aliquot of unknown cyclohexene solution.(a) How many moles of electrons passed through the cell?(b) How
H2S(aq) can be analyzed by titration with coulometrically generated I2.H2S + I2 → + S(s) + 2H+ + 2I-To 50.00 mL of sample were added 4 g of KI. Electrolysis required 812 s at 52.6 mA. Calculate the
Ti3+ is to be generated in 0.10 M HClO4 solution for coulometric reduction of azobenzene.At the counter electrode, water is oxidized, and O2 is liberated at a pressure of 0.20 bar. Both electrodes
In an extremely accurate measurement of the Faraday constant, a pure silver anode was oxidized to Ag+ with a constant current of 0.203 6390 (± 0.0000004) A for 18 000.075 (± 0.010) s to give a mass
How many hours are required for 0.100 mol of electrons to flow through a circuit if the current is 1.00 A?
Coulometric titration of sulfite in wine. Sulfur dioxide is added to many foods as a preservative. In aqueous solution, the following species are in equilibrium:Bisulfite reacts with aldehydes in
Chemical oxygen demand by coulometry. An electrochemical device incorporating photooxidation on a TiO2 surface could replace refluxing with Cr2O72- to measure chemical oxygen demand (Box 15-2). The
What is a Clark electrode, and how does it work?
(a) How does the amperometric glucose monitor in Figure 16-10 work?(b) Why is a mediator advantageous in the glucose monitor?(c) How does the coulometric glucose monitor in Figure 16-12 work?(d) Why
For a rotating disk electrode operating at sufficiently great potential, the redox reaction rate is governed by the rate at which analyte diffuses through the diffusion layer to the electrode. The
In 1 M NH3/1 M NH4Cl solution, Cu2+ is reduced to Cu+ near -0.3 (versus S.C.E.), and Cu+ is reduced to Cu(in Hg) near - 0.6 V.(a) Sketch a qualitative sampled current polarogram for a solution of
(a) Explain the difference between charging current and faradaic current.(b) What is the purpose of waiting 1 s after a voltage pulse before measuring current in sampled current voltammetry?(c) Why
Suppose that the diffusion current in a polarogram for reduction of Cd2+ at a mercury electrode is 14 μA. If the solution contains 25 mL of 0.50 mM Cd2+, what percentage of Cd2+ is reduced in the
The drug Librium gives a polarographic wave with E1/2 = - 0.265 V (versus S.C.E.) in 0.05 M H2SO4. A 50.0-mL sample containing Librium gave a wave height of 0.37 μA. When 2.00 mL of 3.00 mM Librium
Explain what is done in anodic stripping voltammetry. Why is stripping the most sensitive voltammetric technique?
The standard free energy change for the formation of H2(g) + ½O2(g) from H2O is ΔG° = + 237.13 kJ. The reactions areCalculate the standard voltage (E°) needed to decompose water into its elements
The figure below shows a series of standard additions of Cu2+ to acidified tap water measured by anodic stripping voltammetry at an iridium electrode. The unknown and all standard additions were made
From the two standard additions of 50 pm Fe(III) in Figure 16-23, find the concentration of Fe(III) in the seawater. Estimate where the baseline should be drawn for each trace and measure the peak
Peak current (Ip) and scan rate (Ip) are listed for cyclic voltammetry (Fe(II) → Fe(III)) of a water-soluble ferrocene derivative in 0.1 M NaCl.If a graph of Ip versus √v gives a straight line,
What are the advantages of using a microelectrode for voltammetric measurements?
What is the purpose of the Nafion membrane in Figure 16-30?Figure 16-30
Write the chemical reactions that show that 1 mol of I2 is required for 1 mol of H2O in a Karl Fischer titration.
Explain how the end point is detected in a Karl Fischer titration in Figure 16-32.Figure 16-32
Consider the following electrolysis reactions.(a) Calculate the voltage needed to drive the net reaction if current is negligible.(b) Suppose that the cell has a resistance of 2.0 and a current of
Which voltage, V1 or V2, in the diagram (see top of next column), is constant in controlled potential electrolysis? Which are the working, auxiliary, and reference electrodes in the diagram?
The Weston cell is a stable voltage standard formerly used in potentiometers. (The potentiometer compares an unknown voltage with that of the standard. In contrast with the conditions of this
The chlor-alkali process, in which seawater is electrolyzed to produce Cl2 and NaOH, is the second most important commercial electrolysis, behind production of aluminum.The Nafion membrane used to
A lead-acid battery in a car has six cells in series, each delivering close to 2.0 V for a total of 12 V when the battery is discharging. Recharging requires ∼2.4 V per cell, or ∼14 V for the
A 0.326 8-g unknown containing Pb(CH3CHOHCO2)2 (lead lactate, FM 385.3) plus inert material was electrolyzed to produce 0.111 1 g of PbO2 (FM 239.2). Was the PbO2 deposited at the anode or at the
When I was a boy, Uncle Wilbur let me watch as he analyzed the iron content of runoff from his banana ranch. A 25.0-mL sample was acidified with nitric acid and treated with excess KSCN to form a red
The absorption cross section on the ordinate of the ozone absorption spectrum at the beginning of this chapter is defined by the relationwhere n is the number of absorbing molecules per cubic
A compound with molecular mass 292.16 g/mol was dissolved in a 5-mL volumetric flask. A 1.00-mL aliquot was withdrawn, placed in a 10-mL volumetric flask, and diluted to the mark. The absorbance at
You have been sent to India to investigate the occurrence of goiter disease attributed to iodine deficiency. As part of your investigation, you must make field measurements of traces of iodide (I-)
Nitrite ion, NO-2, is a preservative for bacon and other foods, but it is potentially carcinogenic. A spectrophotometric determination of NO-2 makes use of the following reactions:Here is an
(a) How much energy (in kilojoules) is carried by one mole of photons of red light with λ 650 nm?(b) How many kilojoules are carried by one mole of photons of violet light with λ 400 nm?
A 2.00-mL solution of apotransferrin was titrated as illustrated in Figure 17-10. It required 163 L of 1.43 mM ferric nitrilotriacetateto reach the end point.(a) Why does the slope of the
The iron-binding site of transferrin in Figure 17-7 can accommodate certain other metal ions besides Fe3+ and certain other anions besides CO32-. Data are given in the table for the titration of
Gold nanoparticles (Figure 16-29) can be titrated with the oxidizing agent TCNQ in the presence of excess of Br to oxidize Au(0) to AuBr in deaerated toluene. Gold atoms in the interior of the
In formaldehyde, the transition n → π*(T1) occurs at 397 nm, and the n → π*(S1) transition comes at 355 nm. What is the difference in energy (kJ/mol) between the S1 and T1 states? This
What is the difference between fluorescence and phosphorescence?
Explain what happens in Rayleigh scattering and Raman scattering. How much faster is scattering of visible light than fluorescence?
What is the difference between a fluorescence excitation spectrum and a fluorescence emission spectrum? Which one resembles an absorption spectrum?

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