代写LH Physical IIIb / 03 33681 Chemistry Summer Examinations 2021调试R语言程序

COLLEGE OF ENGINEERING & PHYSICAL SCIENCES

SCHOOL OF CHEMISTRY

Year 3 Degree of MSci/BSc with Honours

Chemistry

Chemistry with Industrial Experience

Chemistry with Pharmacology

Chemistry with Business Management

Chemistry with a Modern Language

Degree of B.A./BSc Liberal Arts & Sciences

LH Physical IIIb / 03 33681

Summer Examinations 2021

1.         Giving full justification, suggest the best technique (or combination of techniques) and experimental strategy that could be used to investigate each of the following (a) to (e):

[Do not describe all the details of how the methods work from your notes. Instead you should focus on the key features of the experiment that make it suitable for the situation and explain why other methods may be less suited.]

(a)    the absolute configuration of phenylalanine in crystalline form; (3 marks)

(b)    the structure of the complex formed when RhCl(PPh3)3  attaches to an amorphous polymer; (3 marks)

(c)    the distribution of copper and nickel atoms in the doped perovskite crystalline phase LaNi(1-x)CuxO3 and whether this structure is representative of the bulk sample;  (4 marks)

(d)    the structure of a mixed self-assembled monolayer of octadecanethiol and octanethiol on Au(111); (3 marks)

(e)     whether carbon monoxide is adsorbed on the surface of iridium catalyst particles as C and O atoms or as CO molecules, and whether any adsorbed CO molecules lie parallel or perpendicular to the particle surface. (3 marks)

2.         (a)    A Au(110) surface was modified with iodide ions, with diameter d = 0.2 nm.

After surface modification, STM images of the modified surface were obtained. The expected interatomic distance of the atoms is 0.28 nm and 0.55 nm; however, the STM image shows that the actual distance between the atoms is 0.28 nm and 1.10 nm.

(i)   Explain the phenomenon, fully justifying your answer and illustrating your answer with an appropriate sketch of the surface structure.  (3 marks)

(ii)  Describe how the surface energy of the observed surface differs from the surface energy of the expected surface. Your answer should include the appropriate mathematical expressions and a full justification. (4 marks)

(iii) In order to obtain the STM image of the Au(110) surface modified with iodide ions, a bias potential of 0.3 V was applied between the tip and the surface. When the iodide ions were removed from the surface, only 0.2 V    was required to obtain the image. Explain the phenomenon and fully justify your answer. (3 marks)

(b)    A Pd(100) surface, with work function 4.5 eV, was modified with long-chain alkyl thiols, resulting in a change in the work function of - 1.04 eV.

(i)   Is the process chemisorption or physisorption?  Justify your answer. (2 marks)

(ii)  Explain why the surface energy of the modified surface is different from that of the unmodified surface. (2 marks)

(iii) The temperature desorption programme experiment of the modified surface shows that when the coverage was θ = 0.6, the desorption temperature of the molecules was 350 K and when the coverage was θ = 1, the desorption temperature of the molecules was 400 K.  Explain the phenomenon and fully justify your answer. (2 marks)

3.         (a)    The table below gives the catalytic activity for the hydrogenolysis of

methylamine, CH3NH2, over third row transition metals under a constant set of conditions.  [Catalytic activity has been normalised for surface area and given in arbitrary units.]

Metal	Re	Os	Ir	Pt	Au
Relative catalytic activity	0.008	0.9	100	11	0.5

(i)   Write a balanced equation for the reaction.  (1 mark)

(ii)  Sketch (do not use graph paper) a plot of relative catalytic activity vs

atomic number and name the type of plot that this graph represents.

Explain the pattern of activity observed, given that the rate determining

step is the dissociative chemisorption of methylamine and suggest a way of increasing the activity for platinum. (6 marks)

(iii) Discuss the advantages of developing an effective catalyst based on a first   row transition metal, rather than one using iridium or platinum as the active phase.  (2 marks)

(b)    A catalyst consists of 15.0 wt% Ni dispersed on an alumina support.  On

exposure of the catalyst to carbon monoxide, the CO is selectively chemisorbed onto theNi only.  Data recorded for the chemisorption of CO on a sample of 0.930 g of catalyst at 273 K are given in the table below.  (The volume adsorbed has been corrected to STP, where 1 mole of gas occupies a volume of 22.414 dm3.)

Pressure, p / atm	0.0500	0.100	0.200	0.250
Volume adsorbed, V / cm3	1.13	1.26	1.35	1.37

Confirm that the data fit the Langmuir isotherm, and find the Langmuir constant K and the number of molecules Nm corresponding to complete coverage.  Hence calculate the accessible surface area of the nickel [in m2  (gNi)–1]. (7 marks)