NSEC — National Standard Examination in Chemistry Feed

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For the oxidation-reduction reaction of ferrous oxalate (FeC2O4) with potassium dichromate (K2Cr2O7) in an acidic medium, how many moles of K2Cr2O7 are required to oxidize one mole of FeC2O4 completely?

Physical Chemistry

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An oleum sample is labeled as '109%'. What is the mass percentage of free SO3 in this sample of oleum?

Physical Chemistry

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According to the Bohr model, which electronic transition in a He+ ion will have the same wavelength as the transition from n = 4 to n = 2 in a hydrogen atom?

Physical Chemistry

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What is the total number of radial nodes and angular nodes, respectively, in a 4d orbital of a hydrogen-like atom?

Physical Chemistry

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When a metal surface is illuminated with light of wavelength 300 nm, photoelectric emission occurs. If the work function of the metal is 2.5 eV, what is the maximum kinetic energy of the emitted photoelectrons? (Take hc = 1240 eV-nm)

Physical Chemistry

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Under which conditions does the compressibility factor (Z) of a real gas obeying the van der Waals equation become Z = 1 + (Pb / RT)?

Physical Chemistry

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A vessel contains equal masses of methane (CH4) and oxygen (O2) gases. What is the ratio of the partial pressure of methane to that of oxygen in the vessel?

Physical Chemistry

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Which of the following statements regarding the Maxwell-Boltzmann distribution of molecular speeds for a gas is correct?

Physical Chemistry

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One mole of an ideal gas expands isothermally and reversibly at 300 K from an initial volume of 10 L to a final volume of 100 L. What is the work done by the gas? (Take R = 8.314 J/mol-K, ln 10 = 2.303)

Physical Chemistry

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For a spontaneous endothermic reaction occurring at constant temperature and pressure, which of the following thermodynamic relations must be true?

Physical Chemistry

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The equilibrium constant (K_eq) for a reaction is 10^5 at 298 K. What is the standard Gibbs free energy change (Delta G-degree) for this reaction? (Take R = 8.314 J/mol-K, ln 10 = 2.303)

Physical Chemistry

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Using the following thermochemical data, calculate the lattice energy of NaCl(s): Sublimation energy of Na(s) = +108 kJ/mol Ionization energy of Na(g) = +496 kJ/mol Dissociation energy of Cl2(g) = +242 kJ/mol Electron affinity of Cl(g) = -349 kJ/mol Enthalpy of formation of NaCl(s) = -411 kJ/mol

Physical Chemistry

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The heat of combustion of benzene (C6H6, l) is -3268 kJ/mol, and its theoretical heat of combustion calculated from bond enthalpies assuming three localized C=C bonds is -3520 kJ/mol. What is the resonance stabilization energy of benzene?

Physical Chemistry

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For the equilibrium reaction N2(g) + 3H2(g) <=> 2NH3(g) (Delta H < 0), which of the following changes will shift the equilibrium position to the right?

Physical Chemistry

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At a certain temperature, the vapor density of a mixture containing PCl5 and its dissociation products PCl3 and Cl2 is found to be 70.0. What is the degree of dissociation (alpha) of PCl5 at this temperature? (Molar mass of PCl5 = 208.5 g/mol)

Physical Chemistry

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What is the pH of a buffer solution prepared by mixing 50 mL of 0.2 M acetic acid (CH3COOH) and 50 mL of 0.1 M sodium acetate (CH3COONa)? (pK_a of acetic acid = 4.76)

Physical Chemistry

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The solubility product (K_sp) of AgCl is 1.0 x 10^-10 at 298 K. What is the solubility of AgCl in a 0.1 M NaCl solution?

Physical Chemistry

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Which of the following expressions correctly represents the pH of an aqueous solution of ammonium acetate (NH4CH3COO) at 298 K? (pK_w = 14.0, pK_a of CH3COOH = 4.76, pK_b of NH3 = 4.75)

Physical Chemistry

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The rate constant of a reaction is found to double when the temperature is raised from 300 K to 310 K. What is the activation energy (E_a) of this reaction? (Take R = 8.314 J/mol-K, ln 2 = 0.693)

Physical Chemistry

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A first-order reaction has a rate constant of 2.303 x 10^-3 s^-1. How much time will it take for the concentration of the reactant to reduce to 10% of its initial value?

Physical Chemistry

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For the reaction mechanism: Step 1: A + B <=> C (fast equilibrium, forward rate constant k1, reverse rate constant k_-1) Step 2: C + D -> E (slow, rate constant k2) Which of the following is the correct rate law for the formation of E?

Physical Chemistry

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What is the cell potential of the following cell at 298 K? Zn(s) | Zn2+(0.01 M) || Cu2+(1.0 M) | Cu(s) Given: E-degree(Zn2+/Zn) = -0.76 V, E-degree(Cu2+/Cu) = +0.34 V, and 2.303RT/F = 0.059 V

Physical Chemistry

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How many Faradays of electricity are required to reduce one mole of MnO4- to Mn2+ in an acidic medium?

Physical Chemistry

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At infinite dilution, the limiting molar conductivities (L_degree) of BaCl2, H2SO4, and HCl are 280, 860, and 426 S-cm^2/mol, respectively. What is the limiting molar conductivity of BaSO4?

Physical Chemistry

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Which of the following best describes the shape of the conductometric titration curve when a strong acid (like HCl) is titrated with a strong base (like NaOH)?

Physical Chemistry

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A binary liquid mixture of benzene and toluene behaves almost ideally. At 300 K, the vapor pressure of pure benzene is 100 mmHg and that of pure toluene is 40 mmHg. If a solution contains equal moles of benzene and toluene, what is the mole fraction of benzene in the vapor phase in equilibrium with this solution?

Physical Chemistry

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For a 0.01 m aqueous solution of potassium ferricyanide, K3[Fe(CN)6], the freezing point depression is observed to be 0.062 K. What is the apparent degree of dissociation (alpha) of this complex salt in water? (K_f for water = 1.86 K-kg/mol)

Physical Chemistry

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A 0.1 M solution of a weak monobasic acid is found to have an osmotic pressure of 2.95 atm at 300 K. What is the percent ionization of the acid?

Physical Chemistry

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An element crystallizes in a face-centered cubic (FCC) lattice. If the edge length of the unit cell is 400 pm, what is the closest distance of approach between two atoms of this element?

Physical Chemistry

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Which of the following statements about Frenkel defects in ionic solids is correct?

Physical Chemistry

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In a first-order reflection from a crystal lattice, X-rays of wavelength 1.54 Angstroms are diffracted at an angle of 30 degrees. What is the interplanar spacing (d) of the crystal?

Physical Chemistry

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According to the Freundlich adsorption isotherm, the relationship between the mass of gas adsorbed per gram of adsorbent (x/m) and pressure (P) at moderate pressures is given by x/m = k * P^(1/n). What is the typical range of the value of 1/n?

Physical Chemistry

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According to the Hardy-Schulze rule, which of the following ions will have the highest coagulating power for a negatively charged arsenious sulfide (As2S3) sol?

Physical Chemistry

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Which of the following is a characteristic property of lyophilic colloids compared to lyophobic colloids?

Physical Chemistry

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What happens to the conductivity of a surfactant solution when the concentration reaches the Critical Micelle Concentration (CMC)?

Physical Chemistry

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The first four ionization energies of an element are 578, 1817, 2745, and 11578 kJ/mol. In which group of the periodic table is this element most likely located?

Inorganic Chemistry

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Which of the following represents the correct order of electron gain enthalpy (most negative to least negative) for the halogens and chalcogens listed?

Inorganic Chemistry

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The solubility of alkaline earth metal sulfates in water decreases down the group from MgSO4 to BaSO4. What is the primary thermodynamic reason for this trend?

Inorganic Chemistry

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Using VSEPR theory, predict the shape and the hybridization of the central xenon atom in XeO2F2.

Inorganic Chemistry

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According to Molecular Orbital Theory (MOT), which of the following species is paramagnetic and has a bond order of 1.5?

Inorganic Chemistry

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Why is the dipole moment of NH3 (1.47 D) significantly larger than that of NF3 (0.23 D), even though fluorine is much more electronegative than hydrogen?

Inorganic Chemistry

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Which of the following compounds exhibits the strongest intermolecular hydrogen bonding in the liquid state?

Inorganic Chemistry

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Which of the following properties is shared by lithium and magnesium due to their diagonal relationship?

Inorganic Chemistry

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What is the structural composition of the bridge bonds in a diborane (B2H6) molecule?