The thermal decomposition pathways of the mineral wheatleyite (sodium bis(oxalato)cuprate(II) dihydrate, Na2Cu(C2O4)2⋅2H2O) have not been established with certainty and the enthalpy of formation of wheatleyite has not been reported. Thermogravimetric analysis (TG), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) and powder X-ray diffraction (PXRD) were used to establish the chemical reactions that occur during the thermal decomposition of sodium bis(oxalato)cuprate(II) dihydrate under atmospheres of static air and flowing nitrogen. The decomposition occurred in three steps in either atmosphere, but the decomposition temperature and products produced depended on the atmosphere. The initial step was the loss of water to form Na2Cu(C2O4)2 in either atmosphere. The Na2Cu(C2O4)2 decomposed in the second step to form Na2C2O4 and a copper compound that depended on the carrier gas. Cu was the decomposition product formed in nitrogen while CuO was produced in air. During the final decomposition, Na2C2O4 decomposed to form Na2CO3. Once the decomposition reactions were established, differential scanning calorimetry (DSC) was used to measure the enthalpy of formation for Na2Cu(C2O4)2 and Na2Cu(C2O4)2⋅2H2O in an atmosphere of static air. The values determined for the enthalpies of formation were -2095 kJ mol−1 and -2670 kJ mol−1 for Na2Cu(C2O4)2 and Na2Cu(C2O4)2⋅2H2O respectively with a measured standard deviation of ±5 kJ mol−1 and estimated total uncertainty of ±10 kJ mol−1.

Differential scanning calorimetry (DSC) was used to measure the enthalpies of reaction for the dehydration of the potassium Tutton salts, K2M(SO4)2 . 6 H2O with M = Mg, Co, Ni, Cu and Zn. The values determined ranged from 335 kJ mol−1 for K2Mg(SO4)2 6 H2O to 355 kJ mol−1 for K2Ni(SO4)2. 6 H2O with a measured standard deviation of ± 5 kJ mol−1. Although the information needed to obtain precise values for the enthalpies of formation is not available in the literature for all of these salts, values calculated by modeling the amorphous dehydrated compound as an ideal solid solution produced values within 10 kJ mol−1 of the values determined for K2M(SO4)2. 6 H2O (M= Mg, Cu, and Zn) where the information needed for this calculate was available. DSC was also used to determine the entropies of reaction for the dehydration of these salts. Since there is little information about the entropies of these compounds in the literature, the entropies of reaction were used with the ideal solution model for the amorphous compound to estimate the standard molar entropies for these salts. The values determined ranged from 490 J K−1 mol−1 for K2Cu(SO4)2 . 6 H2O to 540 J K−1 mol−1 for K2Co(SO4)2 . 6 H2O. Since these values are based upon estimated values, they have an estimated error of ± 5 percent.

The dynamics of the thermal dehydration of sodium carbonate monohydrate was investigated using isothermal and non-isothermal thermogravimetric methods for sample masses between 1 and 10 mg in a 70 μl alumina cell. The apparent activation energy determined from isothermal measurements changed from 70 kJ mol−1 for 10 mg samples to 115 kJ mol−1 for 1 mg samples when the data was fit using the AE-2 mechanism. Fitting non-isothermal data using the Starink method produced apparent activation energies were constant within experimental error for 0.05 < α < 0.6 then decreased rapidly for α > 0.6 indicating there were at least two steps in the dehydration mechanism. The values found for 0.05 < α < 0.6 also depended on the sample mass and were 112, 105, and 100 kJ mol−1 for 1, 5 and 10 mg samples respectively. The experimental uncertainty in each of these measurements is ± 5 kJ mol−1. The Arrhenius parameters found for the dehydration reaction by extrapolating the isothermal reaction rates to zero mass where it was assumed that the rehydration reaction was not contributing to the dynamics were Ed = 116 ± 5 kJ mol−1 and Ad = 1.7 ± 0.9 * 1015 s−1. Since the activation energy determined is less than the value of 130 kJ mol−1 obtained using the thermochemical approach these values could still include a contribution from the rehydration reaction and represent a lower bound for these parameters. Using these values and other measured thermodynamic quantities gives Er = 57 ± 5 kJ mol−1 and Ar = 1.3 ± 0.9 * 107 s−1 for the rehydration reaction. This investigation clearly shows that self-generated atmospheres may affect the measured dynamics for a reversible reaction and should be considered when doing the analysis.

Differential scanning calorimetry has been used to measure the enthalpy of formation for manganese, iron, cobalt, nickel, copper and zinc oxalate. By adding a flameless combustion catalyst (CuO) and using scans of 2 K min−1 in static air, the values determined for each compound agreed to within 1% of the critically reviewed values reported previously. Confident in the approach's validity, values for metal oxalates that did not have accepted values in the compilation are also presented. This approach has the potential to measure reliable ΔfH values for any compound where the products can be fully oxidized during the decomposition.

It is easy to obtain the NMR spectra of small alcohol molecules, small hydrocarbons, and water in the vapor phase by placing a small amount of the liquid in the bottom of the outer tube of a coaxial NMR tube and heating it slightly to vaporize the liquid. This chapter presents three possible physical chemistry laboratory exercises that use vapor phase NMR to investigate some aspect of physical chemistry. The first uses the NMR as a spectrometer to investigate the enthalpy of vaporization of a volatile liquid. The second compares the NMR spectrum observed for the neat liquid and the vapor to investigate the effect of hydrogen bonding on the chemical shifts of the OH proton for water or alcohols. The third investigates the effect of paramagnetic oxygen on the chemical shifts observed for vapor molecules in air. We also present our experience with attempting to use NMR remotely.

This chapter contains computational chemistry exercises to explore topics often presented in upper level undergraduate courses. It is used to supplement the classic HCl/DCl infrared spectroscopy experiment, to determine the IR spectra of the isoelectronic series BO2-, CO2, and NO2+ and to assign the IR and Raman spectra of benzene. Computational chemistry can be used to determine the ground state term symbols for atoms and compare them to the predictions made using the aufbau principle and Hund's rules. The final project investigates possible reaction pathways to form the ions found in the mass spectrum of methane.

The thermal dehydration of the potassium Tutton salts K2M(SO4)2·6H2O (M = Mg, Co, Ni, Cu, Zn) was investigated using thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), FTIR, and variable temperature powder X-ray diffraction. While each Tutton salts lost all six waters of hydration when heated to 500 K, the decomposition pathway depended on the divalent metal cation. K2Ni(SO4)2·6H2O lost all six waters in a single step, and K2Cu(SO4)2·6H2O consistently lost water in two steps in capped and uncapped cells. In contrast, multiple decomposition pathways were observed for the magnesium, cobalt, and zinc Tutton salts when capped and uncapped TG cells were used. K2Zn(SO4)2·6H2O lost the waters of hydration in a single step in an uncapped cell and in two steps in a capped cell. Both K2Mg(SO4)2·6H2O and K2Co(SO4)2·6H2O decomposed in a series of steps where the stability of the intermediates depended on the cell configuration. A greater number of phases were often observed in DSC and capped-cells TG experiments. A quasi-equilibrium model is presented that could explain this observation. These results highlight that experimental conditions play a critical role in the observed thermal decomposition pathway of Tutton salts.

The products obtained during the thermal decomposition of ammonium meta-vanadate depend on the configuration of the container, the mass of the sample, the heating rate and the composition of the carrier gas. The decomposition in an uncapped container produced (NH4)2V4O11, NH4V3O8, and V2O5 as the apparent stable products while the products in a capped container were NH4V3O8, and V2Ox where x was between 4 and 5. These differences are attributed to the different amounts of the evolved gases in the cell. EGA-FTIR clearly established that the reduced final product in the capped cell resulted from a reaction between NH3 and the V2O5 formed during the decomposition. A pre-equilibrium kinetics model where the rate of the reverse reaction depends on the partial pressure of the gaseous products in the cell could explain the different reaction intermediates. This model provides a possible explanation for the different apparent activation energies that have been reported for the thermal decomposition of other compounds where a reversible step could occur in the decomposition mechanism.

The dramatic increase in the computing power of computers coupled with rapid advances in relatively low cost software has made it possible to include sophisticated calculations in the undergraduate curriculum. Coupling these calculations with experimental measurements provides insights about a system that cannot be obtained from experimental measurements alone. Since there are no limitations caused the potential hazards or the expense of the chemicals and no instruments needed to make the measurements, calculations can be performed for any system. Examples where DFT-B3LYP-GIAO calculations were used to enhance student knowledge at JMU are presented. These calculations show how electron density and electronegativity of neighboring groups influence the chemical shift observed for the molecule. A project investigating the calculations is also presented.

Thin films of organic semiconductor PEDOT:PSS deposited onto silicon and fused silica substrates. These films were then treated with sulfuric acid (H2SO4) for various amounts of time (i.e., 10, 20, 40, 60, and 80 minutes). Preliminary results obtained with FT-IR, UV-VIS, and Van DerPauw conductivity methods suggest that the H2SO4 removes the PSS isonomer from the PEDOT: PSS system. This PSS removal also induces a decrease in film thickness.

The effect of tungsten doping and hydrogen annealing treatments on the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4) photoanodes for solar water splitting was studied. Thin films of BiVO4 were deposited on ITO-coated glass slides by ultrasonic spray pyrolysis of an aqueous solution containing bismuth nitrate and vanadium oxysulfate. Tungsten doping was achieved by adding either silicotungstic acid (STA) or ammonium metatungstate (AMT) in the aqueous precursor. The 1.7 μm – 2.2 μm thick films exhibited a highly porous microstructure. Undoped films that were reduced at 375 ºC in 3% H2 exhibited the largest photocurrent densities under 0.1 W cm-2 AM1.5 illumination. This performance enhancement was believed to be due to the formation of oxygen vacancies, which are shallow electron donors, in the films. Films doped with 1% or 5% tungsten from either STA or AMT exhibited reduced photoelectrochemical performance and greater sample-to-sample performance variations. Powder X-ray diffraction data of the undoped films indicated that they were comprised primarily of the monoclinic scheelite phase while unidentified phases were also present. Scanning electron microscopy showed slightly different morphology characteristics for the Wdoped films. It is surmised that the addition of W in the deposition process promoted the morphology differences and the formation of different phases, thus reducing the PEC performance of the photoanode samples. Significant PEC performance variability was also observed among films deposited using the described process.

Five laboratory exercises that use the NMR spectrum of methanol and DFT-B3LYP-GIAO calculations are presented. DFT calculations explain the different chemical shifts observed for the OH proton in the liquid, the vapor, and varying concentrations of methanol in solution. The equilibrium constant for the methanol dimer is determined from the change in the OH chemical shift observed in the vapor phase NMR spectrum as the temperature is changed. The hydrogen bond energy between methanol and common NMR solvents and the activity coefficient at infinite dilution are determined using the OH chemical shift observed for infinitely dilute solutions. A procedure for measuring the mass susceptibility and magnetic moment of O-2 is also presented.

The adhesion of vapor deposited Au and Pt thin films onto poly(methyl methacrylate) (PMMA) substrates can be significantly enhanced by either spin‐casting or vapor‐exposure to hydrohalocarbon solvents prior to metal deposition. X‐ray photoelectron spectroscopy (XPS) and evolved gas analysis Fourier transform infrared spectroscopy detect residual halogenated solvent at the PMMA surface which chemically activates the surface. Density functional theory (DFT) calculations show that the solvent molecules form a Lewis acid‐base adduct with the ester oxygens in PMMA. DFT predicts that the deposited metal atom (M) inserts into the C–halogen (X) bond on either CHCl3 or CHBr3 to form a O–M–X interaction. This is consistent with M–X bonding observed in high resolution XPS. A model is proposed in which the bond energy of the C–X bond of the solvent must be weak enough so that it can be cleaved by the metal atom to form a M–X bond. A negative control of PMMA exposed to CHF3 is shown to have no effect on Au or Pt adhesion since the bond dissociation energy of the C–F bond is stronger than the C–Cl and C–Br bond energy compared to the metal halide bond energies.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Alan K. Mo, Thomas C. DeVore, Brian H. Augustine, Vezekile P. Zungu, Laura L. Lee, Wm. Christopher Hughes; Improving the adhesion of Au thin films onto poly(methyl methacrylate) substrates using spun-cast organic solvents. J. Vac. Sci. Technol. A 1 May 2011; 29 (3): 030601. https://doi.org/10.1116/1.3562167 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAVS: Science & Technology of Materials Interfaces and ProcessingJournal of Vacuum Science & Technology A Search Advanced Search |Citation Search