India 2013 — incho2013-Q.pdf

Fonte: gare di altri paesi/India/chimica/incho2013-Q.pdf · Apri PDF · apri PDF p.3 Cluster: Termodinamica Soluzioni (stessa cartella): · · · · · · · · · · · · · ·

Problema 1

Problem 1

20 marks Free radicals

Carbon free radicals are trivalent carbon species containing an unpaired electron. They are involved in many synthetic, environmental and biochemical reactions. They are generated by photochemical, thermal or redox reactions through homolytic fission. Both electron donating and electron withdrawing groups stabilize a radical and such radicals are known as nucleophilic and electrophilic radicals respectively. 1.1 The correct order of stability for the following radicals is

a) A > B > C > D

c) D > A > B > C b) B > D > A > C

d) C > A > B > D (1 mark)

One of the common reactions which free radicals undergo is hydrogen abstraction to generate new radicals. 1.2 For the following compound, the correct order of ease with which hydrogen abstraction takes place from carbons numbered as 1 to 6 is

a) 2 > 6 > 4=5 > 1> 3 c) 1 > 2 > 6 > 3 > 4=5 b) 2 > 1 > 6 > 3 > 4=5 d) 6 > 1 > 2 >4=5 > 3

(1.5 marks) 1.3 Halogenation of alkanes with molecular halogen in the presence of light takes place by radical mechanism. When n-butane is chlorinated with chlorine in the presence of light, the yields of 1-chlorobutane and 2-chlorobutane are 28% and 72% respectively. Calculate the ratio of relative reactivities of the hydrogens at C1 and C2 positions.

Name of Student

Roll No.

1 2 3 4 5 6 . (CH3)3C . PhCH2 . CH3CH2 . Indian National Chemistry Olympiad

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(1.5 marks) 1.4 The number of possible dichloro products, including stereoisomers formed when (S)-2-chlorobutane reacts with chlorine in presence of light is

a) 6 b) 3 c) 4 d) 5

(1mark) 1.5 Oxygen exists as a diradical and many organic compounds undergo air oxidation in the presence of light to give hydroperoxides. Draw the structure of the hydroperoxide (A) formed when tetrahydrofuran (THF) undergoes air oxidation.

(1 mark)

1.6 Polyunsaturated fatty acids in oils undergo enzymatic air oxidation resulting in rancidity of the oils. Draw the structure/s of the product/s responsible for the rancidity of linoleic acid (the product contains conjugation).

C1:C2 = Linoleic acid enzyme B O2 / h A Indian National Chemistry Olympiad

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B

(1.5 marks) 1.7 An antioxidant like vitamin E is used as preservative for compounds that can undergo oxidation. Antioxidants react with radicals which are responsible for oxidation. Draw the structure of the radical C generated by the reaction of vitamin E with the radical $RO\cdot$.

(1 mark) 1.8 Radical C in 1.7 is stable because of

a) hyperconjugation c) steric hindrance

b) delocalisation d) electromeric effect

(0.5 mark)

C Me Me Me Me . C RO Indian National Chemistry Olympiad

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E

Dimerisation of radical intermediates generated by single electron transfer from metal ions are very useful in carbon-carbon bond formation. Some of them are given below

a) Pinacol type coupling b) Acyloin condensation c) Coupling of alkynes

1.9 Suggest suitable starting compounds to prepare the compounds in i) and ii) below by a single step involving a radical intermediate. i) Intermediate (E) which is used in the synthesis of anticancer drug taxol.

(1 mark)

i) NaEt2O ii) H3O+ i) Mg, benzene, ${}^{\circ }$C ii) H+ Cu(OAc) / pyridine Indian National Chemistry Olympiad

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ii) Intermediate (F) which is used in the synthesis of Exaltolide used in perfumes.

(1 mark)

Dehalogenation of an organic halide can be brought about via a radical reaction using tributyltin hydride (Bu3SnH) and azobisisobutyronitrile (AIBN). AIBN acts as an initiator to generate Bu3Sn ̇ radical which in turn reacts with RX to generate the alkyl radical R ̇ which is highly reactive. Bu3SnH also acts as a hydrogen donor. (In general, formation of 5/6 membered rings is more favourable as compared to smaller/larger ring systems). 1.10 Give the structure of product G formed in the following reaction. One mole of G consumes one mole of hydrogen on hydrogenation.

(1.5 marks) 1.11 The following synthesis yields a compound (K) that is responsible for the secretions of the glands of various bees and flies. Draw the structures of H-K (Compound J gives a orange red ppt with 2,4-DNP while K does not).

F Bu3SnH, AIBN G (C17H26O2) Indian National Chemistry Olympiad

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(4 marks)

1.12 Mn(OAc)3 is used as a single electron oxidant in C-C bond forming reactions. Metal ions (Mn+) in the higher oxidation state can abstract hydrogen to form radical.

Metal ions (Mn+) can also abstract an electron from a radical to form carbocation.

Draw the structures of M-P in the following reaction scheme.

H C

R

CH

R 2 M 3 + n

Bu3SnH /AIBN ii) Bu3SnH i) ii) H3O+ H (C11H20O3) I (C11H20O3) Indian National Chemistry Olympiad

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(3.5 marks)

Mn(OAc)3 N (radical) heat Mn+3 H+ (C12H12O) P does not decolourise Br Indian National Chemistry Olympiad

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I I

Topic: Thermodynamics, Special Relativity, Nuclear & Particle Physics Metodi: First Law of Thermodynamics, Thermodynamic Cycle Analysis, Ideal Gas Law, Lorentz Transformation Competenze: Mathematical Modeling Fonte: Testo (PDF) — p.3

Problema 2

Problem 2

18 marks Transition Metal Chemistry

Carbon monoxide (CO) is a colorless, odorless and tasteless gas that is lighter than air and highly toxic to humans. 2.1 Draw the resonance structures (Lewis structures) of carbon monoxide (CO) and underline the one which follows the octet rule.

(1.5 marks)

Carbon monoxide forms many metal carbonyls with transition metals in which there is a Metal-Carbon bond. 2.2 Four possibilities of metal carbonyl bondings are given below, in which the metal (M) is in its lower oxidation state. Select the most favourable bonding type.

(1.5 marks)

*(CO) d)

a) c)

*(CO)

b)

*(CO)

CO) *(M)

Name of Student

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2.3 Using the effective atomic number (EAN) rule identify the value of x and y metal carbonyls I and II, draw the structures of the metal carbonyls. I) Crx(CO)y

x =

y =

II) [Mnx(CO)y] x =

y =

(3.5 marks) According to the Valence Bond Theory (VBT), the metal atom or ion under the influence of the ligands can use its (n-1)d, ns, np and nd orbitals for hybridization. These hybrid orbitals overlap with ligand orbitals that can donate electron pairs for bonding. The symbol indicates electrons in metal and the symbol xx indicates electrons from the ligand. (Write approprite alphabets in the boxes) 2.4 Using VBT match the complexes (1-3) with appropriate hybridization schemes (a-c). Complex

Hybridization scheme

(2 marks)

I

II XX XX XX XX XX XX XX XX XX XX XX XX Indian National Chemistry Olympiad

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Metal carbonyls can be synthesized by disproportionation reactions wherein one part of the reactant is oxidised and the other part is reduced. 2.5 Write a balanced chemical equation of the reaction for the synthesis of nickel carbonyl from an appropriate cyanide.

(1 mark)

The infrared stretching frequency in terms of wavenumber $\bar{\nu }$ and expressed in units of ${\text{cm}}^{-1}$ is given as $\bar{\nu }=\frac{1}{2\pi c}\sqrt{k/\mu }$ (where $c$ is the velocity of light, $k$ is force constant and $\mu$ is reduced mass).

2.6 Using the value of force constant as $1854{\text{N m}}^{-1}$, calculate the stretching frequency of free CO molecule.

(2 marks)

A major consequence of the synergic bonding in metal carbonyls is the reduction in the bond order of the C-O bond which results in the lowering of the CO stretching frequency. Any effect which decreases C-O bond order should necessarily increase M-C bond order as the two are complementary to each other. Indian National Chemistry Olympiad

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2.7 Arrange the given metal carbonyls according to the descending order of C-O stretching frequency. (Write approprite alphabets in the boxes) i) a) MCO

b) M2CO

c) M3CO

where M stands for metal.

ii)

(1.5 marks) 2.8 With respect to the complex Co2(CO)8 answer the following. In the IR spectrum, this complex in the solid form shows separate bands, above and below $2000{\text{cm}}^{-1}$.

i) Draw the structure of the complex in the solid form.

ii) When it is dissolved in hexane the bands below $2000{\text{cm}}^{-1}$ disappear. Draw the structure of the complex in the solution.

(2 marks)

a) b) c) Indian National Chemistry Olympiad

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Hydroformylation (Oxo process) is the conversion of olefins to aldehydes catalyzed by cobalt and rhodium carbonyl complexes. A catalytic cycle for the hydroformylation of a terminal olefin is given below and the steps in this cycle are labeled from 1 to 7.

HCo(CO)4 HCo(CO)3 HCo(Co)3(CH2= CHR) CH2= CHR RCH2CH2Co(CO)3 RCH2CH2Co(CO)4 RCH2CH2COCo(CO)3 RCH2CH2COCo(H2)(CO)3 H2 RCH2CH2CHO 1

2 3 4 5 6 7 Indian National Chemistry Olympiad

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2.9 The steps given in the diagram can involve any of the following reactions:

a) ligand substitution and dissociation b) reductive elimination c) - olefin coordination d) olefin insertion e) oxidative addition f) alkyl migration. Using the given information, complete the following table.

(3 marks)

Step No. Reaction type (Choose from the above list and write only the alphabet) Formal oxidation state of metal in the product obtained at the end of the step Number of d electrons 3

6

7 Indian National Chemistry Olympiad

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Topic: Oscillations & Waves, Thermodynamics, Gravitation Metodi: Simple Harmonic Motion Analysis, Wave Equation, Superposition Principle, First Law of Thermodynamics Competenze: Mathematical Modeling Fonte: Testo (PDF) — p.10

Problema 3

Problem 3

14 marks Synthesis of natural products

Natural products have played a pivotal role in the development of Organic Chemistry. Synthesis of a natural product by an unequivocal route is used to establish its structure.

A commercially important natural product A forms an orange–yellow precipitate with 2,4-DNP reagent. It does not react with [Ag(NH3)2]NO3 solution. A on reduction with NaBH4 gives a secondary alcohol and on oxidation with nitric acid yields a dicarboxylic acid containing the same number of carbon atoms. On bromination, A gives a monobromo product. 3.1 On the basis of above observations, A contains (Mark X in the correct box/es) (a) aldehydic carbonyl

(b) ketonic carbonyl (c) ester carbonyl

(d) no unsaturation (e) C=C

(1 mark)

Oxidation of A with nitric acid gives B (C10H16O4) and further oxidation of B gives C (C9H14O6). 3.2 78 mg of B (C10H16O4) requires 15.6 mL of 0.05 M KOH for complete neutralization and 85 mg of C (C9H14O6) requires 23.4 mL of 0.05 M KOH for complete neutralization. Calculate the number of acidic functional groups present in B and C.

(1 mark) Name of Student

Roll No. Indian National Chemistry Olympiad

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Perkin Jr. and Thorpe synthesised C (C9H14O6) using methyl acetoacetate as per the reaction sequence presented below. 3.3 Identify and draw the structures of the reagent (P) and intermediate products (D, E) and compound C. (An $\alpha$-haloester and zinc metal react to form an organozinc reagent analogous to the Grignard reagent.)

(3 marks) 3.5 Draw the Fisher projection formula/e of possible stereoisomers of C and assign the proper stereodescriptor/s.

(1.5 marks)

i) EtONa ii) (i) Zn, BrCH2COOCH3 i) PCl5 ii) KCN Hydrolysis Indian National Chemistry Olympiad

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3.6 Compound H is an intermediate required for the synthesis of A. It is synthesised from diethyl malonate by the following route. Identify reactant Y, intermediates F, G and compound H.

(3.5 marks)

CH2(COOC2H5)2 i) EtONa ii) COOC2H5 i) Ba(OH)2 ii) H3O+ F (C8H12O2) i) NaOBr ii) HCl COOC2H5 H Indian National Chemistry Olympiad

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3.7 Diethyl 3,3-dimethyl pentanedioate is used to prepare B (C10H16O4) as follows. Draw the structures of compounds I, J, K and B.

(3 marks) 3.8 The IUPAC name of (B) is

(1 mark)

B ii) CH3I(1 mole) NaBH4 i) HBr ii) Zn / CH3COOH C2H5ONa HI Indian National Chemistry Olympiad

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Topic: Oscillations & Waves Metodi: Simple Harmonic Motion Analysis, Wave Equation, Superposition Principle Competenze: Mathematical Modeling Fonte: Testo (PDF) — p.16

Problema 4

Problem 4

18 marks Hydrogen as a fuel A. The rapid depletion of fossil fuels has inspired extensive research in the area of alternate and renewable energy sources. Of these, hydrogen is the most contemplated fuel of the future. However, cost effective production and hazard free storage are major issues in using H2. (Note: Use the data in table 1 given at the end of Part A, wherever necessary). 4.1 A cylinder contains hydrogen at a pressure of $80\text{MPa}$ at $25{}^{\circ }\text{C}$. Assuming ideal behaviour, calculate the density of hydrogen in the cylinder in ${\text{kg/m}}^3$.

(1 mark) 4.2 Assuming complete combustion, calculate heat of combustion when

(i) 1 g of hydrogen and (ii) 1 g of carbon are burnt.

(1 mark) 4.3 $1\text{kg}$ of hydrogen is burnt with oxygen at $25{}^{\circ }\text{C}$ and the heat energy is used for different purposes. Using this heat, calculate

(i) the maximum theoretical work.

(ii) work that can be produced by a heat engine working between $25{}^{\circ }\text{C}$ to $300{}^{\circ }\text{C}$. (The efficiency of a heat engine = work done/ heat absorbed = $[1-(T_{\text{low}}/T_{\text{high}})]$ where $T$ is in K)

Name of Student

Roll No. Indian National Chemistry Olympiad

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(2 marks) 4.4 If the maximum theoretical work (calculated in 4.3(i)) is used to run an electric motor of $1\text{Watt}$, under standard potential conditions,

(i) for how many months the motor will run?

(ii)What is the value of the current produced by this motor? (Assume 30 days in all months.)

(2 marks) Table 1

H2 (g) O2 (g) H2 O (l) $S_{298\text{K}}^{\circ }$ / J mol K${}^{-1}$ 131 205 70

H2O (l) CO2 (g)

$\Delta H_f^0$ / kJmol${}^{-1}$ $-286{\text{kJmol}}^{-1}$ $-394{\text{kJmol}}^{-1}$ Indian National Chemistry Olympiad

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B. One method to produce hydrogen on an industrial scale is the reaction of methane with overheated water vapour at 1100 K to form hydrogen and carbon monoxide. The reaction is known as ‘steam reforming’. 4.5 Write the balanced equation for the steam reforming of methane

(0.5 mark)

4.6 The KP of the reforming reaction at 1100K is 28.6. When 1 kmol of methane and

1 kmol of water are reacted at 1100K, calculate the percentage conversion of methane at equilibrium at a total initial pressure of 1.6 bar.

(2 marks) Indian National Chemistry Olympiad

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In another experiment, 1.0 kmol of CH4 and 1.0 kmol of H2O are taken in a sealed vessel at 400 K and 1.6 bar. The temperature is raised to 1100 K. 4.7 Calculate the pressure in the vessel at 1100 K and the % conversion of methane.

(2 marks) C. Heat engines and refrigerators

A heat engine is a system that converts heat into mechanical work. A heat “source” generates thermal energy that brings a working substance to a high temperature. The working substance then generates work in the engine while transferring heat to a sink at a lower temperature. The working of a heat engine is shown figure 1.

(Figure 1)

(Figure 2) Indian National Chemistry Olympiad

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Heat engines can be modelled using thermodynamic cycles. The heat engine given in Figure 2 is of a working substance which is 1.00 mol of a monatomic ideal gas. The thermodynamic cycle begins at the point designated as ‘1’ and goes clockwise and the values of P and/or V at each point is as given below: $P_1=1.00\text{atm}$ and $V_1=24.6\text{L}$; $P_2=2.00\text{atm}$; $V_3=49.2\text{L}$; $P_4=1.00\text{atm}$. 4.8 Calculate $T_1$, $T_2$, $T_3$ and $T_4$.

(2 marks) Indian National Chemistry Olympiad

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4.9 Calculate $\Delta E$ for the paths i) $1\to 2$ ii) $2\to 3$ iii) $3\to 4$ iv) $4\to 1$

(2 marks)

The heat engine depicted in this problem is a ‘Carnot heat engine’ and the thermodynamic cycle of operations of this engine is known as a ‘carnot cycle’, named after Saudi Carnot, an engineer cum thermodynamist. The efficiency of a carnot Indian National Chemistry Olympiad

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engine is defined as $(1-T_1/T_2)$ where $T_1$ and $T_2$ are the temperatures of the sink and the source. 4.10 Calculate the efficiency of the cycle given in figure 2.

(1.5 marks)

Another system completes a cycle consisting of six quasi-static steps, during which the total work done by the system is 100 J. During step 1 the system absorbs 300 J of heat from a reservoir at 300 K, during step 3 the system absorbs 200 J of heat from a reservoir at 400 K, and during step 5 it absorbs heat from a reservoir at temperature $T_3$. Steps 2, 4, 6 are adiabatic such that the temperature of one reservoir changes to that of next. 4.11 a) What is the entropy change of the system for the complete cycle?

b) If the cycle is reversible, what is the temperature $T_3$?

(2 marks) Indian National Chemistry Olympiad

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Topic: Thermodynamics Metodi: Ideal Gas Law, Thermodynamic Cycle Analysis, First Law of Thermodynamics Competenze: Mathematical Modeling, Physical Reasoning Fonte: Testo (PDF) — p.20

Problema 5

Problem 5

15 marks Acid-Base Equilibria

The transport of gases through circulation is an important function of blood in the body. CO2 generated in our body dissolves in the blood and is in equilibrium with CO2 in gas phase. A complete representation of CO2 buffer system in the body is shown below.

CO2 (g) CO2 (dissolved)

$K=3.01\times 10^{-5}$ $\dots \dots \dots \dots (i)$

CO2 (dissolved) + H2O H2CO3 (aq) $K_{\text{eq}}=5\times 10^{-3}$ $\dots \dots \dots \dots (ii)$

H2CO3 (aq) H+ (aq) + HCO3 ̄(aq) $K_{a1}=1.58\times 10^{-4}$ $\dots \dots \dots (iii)$

HCO3 ̄ (aq) H+ (aq) + CO3 2 (aq)

$K_{a2}=5.6\times 10^{-11}$ $\dots \dots$.. (iv)

When $p_{{\text{CO}}_2}$ is expressed in terms of mm Hg, the values of $K$, $K_{a1}$ and $K_{a2}$ given above are at $37{}^{\circ }\text{C}$. 5.1 Calculate the value of overall equilibrium constant $K_a^{\prime }$, for the equilibrium between H+, [HCO3 ̄] (aq) and CO2 dissolved.

(1 mark)

In vivo, the (HCO3 ̄/CO2) is an open system in which [CO2]dissolved is maintained constant and any excess CO2 produced by the reaction

H+(aq)+ HCO3 ̄(aq) CO2 + H2O is expelled out by the lungs. This reaction is responsible for maintaining the pH of blood. We will understand the effectiveness of this open system through the following example:

A total carbonate pool (essentially [HCO3 ̄]+ CO2) in blood plasma is

$2.52\times 10^{-2}$ M. 5.2 i) The pH of blood in the body is maintained at 7.4. What is the ratio of [HCO3 ̄]/[CO2] and the concentration of each component present at pH 7.4? Name of Student

Roll No 2 co p Indian National Chemistry Olympiad

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(2 marks) ii) What would be the pH of the blood if $5\times 10^{-3}$ M H+ is added under conditions where the increased [CO2] cannot be exhaled out?

(1.5 marks) iii) What would be the pH if $5\times 10^{-3}$ M [H+] is added and the increased [CO2] is exhaled out? (thereby the original [CO2] does not change)

(0.5 mark) 5.3 If a person exhales $274{\text{mL min}}^{-1}$ of CO2 at $37{}^{\circ }\text{C}$ and $101.3\text{kPa}$ pressure, calculate [CO2] and [HCO3 ̄] in CO2 rich blood. (Blood flows through the lungs at a rate of $5.4{\text{L min}}^{-1}$) Indian National Chemistry Olympiad

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(3 marks) In the body, haemoglobin binds with O2. The O2 binding curves for haemoglobin in presence and absence of CO2 is qualitatively sketched below. The curves indicate percent saturation of haemoglobin by O2 as a function of partial pressure of O2.

2 o p 100

0 In presence of CO2 In absence of CO2 Percent saturated Indian National Chemistry Olympiad

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2 o p 2 o p 2 o p 2 o p 5.4 Which of the following statement/s is/are correct for the given curves?

i) In presence of CO2, higher is needed for a given percent saturation

ii) In presence of CO2, lower is needed for a given percent saturation iii) In absence of CO2, maximum saturation of haemoglobin occurs at lower

iv) In absence of CO2 for any given percent saturation, higher is needed

(1 mark)

Each Haemoglobin (Hb) molecule can take up four molecules of O2. In the following figure oxygenated fraction of haemoglobin is plotted as a function of oxygen pressure in kPa. The curves in the figure are for different types of haemoglobin, namely, normal (curve 1) and abnormal (curves 2 and 3). (O2 pressure in lungs, and muscles is 15 kPa and 2 kPa respectively.)

5.5 Using the figure given above, calculate the number of moles of O2 absorbed in muscle tissues when one mole of (Hb) travels from the lungs to the muscles and back again, in all three types of (Hb) shown in the figure.

(1 mark)

In intense physical activity, lactic acid is produced in the muscles, particularly in an anaerobic metabolism. High lactic acid/lactate ([HL]/[L ̄]) levels in muscles lead to high acidity and destruction of other metabolites. In blood, lactic acid (HL)

($K_{\text{HL}}=1.4\times 10^{-4}$) is neutralised by the bicarbonate present in the blood. Indian National Chemistry Olympiad

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5.6 Calculate the pH of blood in muscles when the lactic acid concentration is

$2.70\times 10^{-3}$ M.

(1 mark) 5.7 Calculate the equilibrium constant for the reaction between lactic acid and bicarbonate. Write the equations for the appropriate equilibria involved. (For this calculation, assume the dissociation constants of H2CO3 as $K_{a1}=4.5\times 10^{-7}$ and $K_{a2}=4.7\times 10^{-11}$).

(2 marks) 5.8 Blood also contains Ca (II) ions. Determine the maximum concentration of calcium ions that can be present in blood at pH = 7.4.

($[{\text{HCO}}_3^{-}]=0.022$ M at this pH and for simplification assume that only Ca will precipitate as CaCO3. $K_{\text{sp}}$ of CaCO3 $=4.9\times 10^{-9}$)

(2 marks) Indian National Chemistry Olympiad

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Topic: Thermodynamics Metodi: First Law of Thermodynamics, Thermodynamic Cycle Analysis, Ideal Gas Law Competenze: Mathematical Modeling Fonte: Testo (PDF) — p.27

Problema 6

Problem 6 12 marks Electrochemistry

Electrochemistry encompasses synthesis of molecules, analysis of diverse and trace materials and also technological applications such as fuel cells and batteries. Electrochemical potential is a key parameter of electrochemistry. Walther Nernst, a Nobel prize winning German physicist cum chemist, formulated a valuable equation that relates the actual reversible potential of an electrode to its standard reversible potential $E^{\circ }$, a thermodynamic quantity. I For all the calculations, assume i) concentration can be used in place of activity. ii) The temperature of the electrochemical cells is $25{}^{\circ }\text{C}$, unless specified otherwise. II Use Table I given at the end of this problem of electrochemical potentials to solve the problems. 6.1 For the cell Ag(s) | Ag2SO4(s) || H2SO4 | H2 (1 atm) | Pt a) Write the half cell reactions and the overall reaction.

(1.5 marks) b) Calculate E of the cell if $E^{\circ }$ is $-0.627\text{V}$ and the concentration of H2SO4 is $0.1\text{M}$.

(0.5 mark)

Name of Student

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c) Which of the following statement/s is/are true for the given cell? i) The given cell requires a salt bridge ii) The given cell does not require a salt bridge iii) It is not possible to draw current from the cell as represented iv) It is possible to draw current from the cell as represented

(1 mark)

6.2 For the cell, Ag(s) | Ag2SO4 (0.02M) || CdSO4 (0.016M) | Cd(s) a) Calculate the equilibrium constant at $25{}^{\circ }\text{C}$ for the overall cell reaction

(1.5 marks) b) Which of the following statement/s is/ are correct for the above cell?

i) E will be less negative at $35{}^{\circ }\text{C}$

ii) E will be more negative at $25{}^{\circ }\text{C}$

iii) E does not change with temperature

(1 mark) Indian National Chemistry Olympiad

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6.3 Using the data in Table I a) Calculate the equilibrium constant for the reaction, $\text{Cu(s)}+{\text{Cu}}^{2+}\text{(aq)}\rightleftharpoons 2{\text{Cu}}^{+}$

(2 marks) b) What is the equilibrium concentration of Cu+ ions when excess Cu(s) is added to 0.01M Cu2+ solution?

(1 mark) 6.4 A solution of 0.01M SnCl2 and 0.1M KCl was suspected to contain PbCl2. The lead content was determined by electrodeposition using a Pt cathode and a

Ag /AgCl anode. The electrolysis was stopped when the Sn just started to deposit on the cathode (the shiny metallic lustre of Sn makes it visually possible). a) Write the cell reaction for the deposition of Pb.

(0.5 mark) Indian National Chemistry Olympiad

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b) Calculate the final Pb2+ concentration in the solution.

(3 marks)

Table I Redox system (aq) Electrode potential at $25{}^{\circ }\text{C}$ (V) Redox system (aq)

Electrode potential at $25{}^{\circ }\text{C}$ (V) Ag+/ Ag 0.800 Pb2+/ Pb $-0.126$ Cd2+/ Cd $-0.400$ Sn2+/ Sn $-0.140$ Cu+/ Cu 0.521 Cu2+/Cu $-0.339$

Topic: Thermodynamics, Modern-Quantum Physics, Astrophysics Metodi: First Law of Thermodynamics, Thermodynamic Cycle Analysis, Ideal Gas Law, Photon Energy Relation Competenze: Mathematical Modeling, Estimation & Approximation Fonte: Testo (PDF) — p.32