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Nagoya University Entrance Examination (Year 2012) :Chemistry

Chemistry exam time limit: approximately 75 minutes; *A total of 150 minutes is allocated for the combination of the Chemistry exam and the other science category exam.



Chemistry Problem I

Read the following text and answer Questions (1)–(7). Note: Each gas is a real gas; however, treat nitrogen as an ideal gas under all conditions, and treat water vapor as an ideal gas until instructed otherwise in the underlined section 2.

As shown in the following figure, an experiment is conducted using a container with two enclosed spaces, Spaces A and B, separated by a smoothly movable wall that shifts position to balance the pressures in Spaces A and B. The system is sealed by a piston, as shown. The container is maintained at a constant temperature of 100°C throughout the experiment. Nitrogen (N2) and water vapor (H2O) are present in Spaces A and B, respectively. The volumes and pressures of Spaces A and B are VA and VB and PA and PB, respectively. In the initial state, 1VA = 20 L, PA = 5.065 × 104 Pa, and VB = 20 L, PB = 5. 065 × 104 Pa. The piston is slowly pushed to change VB. 2As PB increases to 1.013 × 105 Pa, a phenomenon is observed in Space B. The piston is further pushed to change VB. After some period of time, 3VB ceases to change significantly.




Question (1): Calculate the mass of nitrogen present in Space A under the conditions described in the underlined section 1. Answers should be given with two significant figures. Clearly show all work.

Question (2): Briefly explain, in 30 words or fewer, the phenomenon observed in Space B during the process underlined in 2.

Question (3): Provide the most appropriate terms for spaces ( A ) and ( B ) below.

"The phenomenon observed during the process underlined in 2 occurs because vapor is not an ideal gas. In order for a gas to behave ideally, the following two conditions must hold: the gas must not have  ( A ) and ( B )  between gas molecules must be insignificant."

Question (4): If VB = 14 L, what is the value of PB in Pa? Answers should be given with two significant figures.

Question (5): Plot the relationship between PB and VB as VB decreases from 20 L to 2 L, using VB as the horizontal axis and PB as the vertical axis. Indicate the point on the graph at which VB = 14 L using a cross mark (×) (Use the plot sheets below).

Question (6): Plot the relationship between VA and VB as VB decreases from 20 L to 2 L, using VB as the horizontal axis and VA as the vertical axis (Use the plot sheets below).



Question (7): At the point at which VB no longer changes, as described in the underlined section 3, what is the value of VB in L? Answers should be given with two significant figures. Clearly show all work. Note that the density of water in Space B is 0.96 g/cm3 under these conditions.


Chemistry Problem II

Problem II-l. Read the following text and answer Questions (1)–(5). Note: During the reactions, the temperature of the container is constant, and the volume of solid and its sublimation can be neglected. All gases are ideal.

 

A total of n mol CO2 is present in a high-temperature container sealed by a piston that moves smoothly to balance the internal pressure of the container with the external pressure P0. When a sufficient quantity of solid carbon (C) is added to the container, holding the position of the piston fixed, CO is produced through the following reaction, and the system reaches a new equilibrium state.

 

C (solid) + CO2 (gas)  2CO (gas)  [1]

 

The partial pressures of CO2 and CO in the equilibrium state are P(CO2) and P(CO), respectively, and the equilibrium constant expressed in terms of partial pressures is Kp. The following relationship holds:

.

 

Kp is constant at any given temperature.


 

Question (1): Setting the fraction of reacted CO2 to α (0 < α < 1), provide an expression for the moles of CO2 and CO in the container at equilibrium.

Question (2):  In terms of α and P0, express the total pressure of gases in the container after the system has reached the equilibrium described in the underlined section above.

Question (3): Express α in terms of P0 and Kp under the equilibrium conditions described in the underlined section.

Question (4): How will the equilibrium described in equation [1] change if the piston is permitted to move freely? Choose the most appropriate explanation from A–C below and describe your reasoning.

A. The equilibrium shifts to the left.      B. The equilibrium does not change.

C. The equilibrium shifts to the right.

Question (5): If the total pressure is increased by adding argon gas while holding the position of the piston fixed, how will the equilibrium described in equation [1] change? Choose the most appropriate explanation from A–C below and describe your reasoning.

A. The equilibrium shifts to the left.      B. The equilibrium does not change.

C. The equilibrium shifts to the right.


Problem II-2. Read the following text and answer Questions (1)–(5).

1The reaction of nitrogen with hydrogen at high temperatures, high pressures, and in the presence of a catalyst containing mainly iron yields ammonia (NH3). Ammonia is an industrially important intermediate. For example, nitric acid (HNO3) is industrially produced from ammonia through the reaction steps explained below.

2The reaction of ammonia with oxygen at high temperatures in the presence of platinum, which acts as a catalyst, yields nitrogen monoxide (NO). Nitrogen monoxide further reacts with oxygen to form nitrogen dioxide (NO2). 3The reaction of nitrogen dioxide with water yields nitric acid. Nitrogen monoxide and nitrogen dioxide are the most prevalent of the nitrogen oxides (NOx), which cause atmospheric pollution.

The reaction of ammonia with carbon dioxide at high temperatures induces a dehydration condensation reaction, yielding urea, CO(NH2)2. Urea is used in devices to clean nitrogen oxides from exhaust gases produced when fuel, such as oil, is burned. For example, diesel engines in automobiles are designed such that an aqueous solution of urea is injected into the combustion exhaust gas to hydrolyze urea and produce ammonia. Ammonia reduces nitrogen monoxide to nitrogen through the reaction described in equation [1].

 
4NH3 + 4NO +O4N2 + 6H2O  [1]

 

Question (1): Provide the name of the industrial method described in the underlined section 1.

Question (2): Provide the chemical equations associated with each of the reaction processes described in the underlined 2 and 3.

Question (3): How many kilograms of urea are necessary to produce the quantity of ammonia needed to dissolve 1.0 kg of nitrogen monoxide through the reaction described in equation [1]? Answers should be given with two significant figures.

Question (4): The thermochemical equations associated with the dissolution of ammonia and urea in water are given below. When obtaining 1.0 kg of a solution by dissolving a mixture of 17 g of ammonia and 15 g of urea in water at 20oC, what is the temperature in oC of the obtained solution? Answers should be given with two significant figures. Note: the amount of heat necessary to raise the temperature of 1 g of this solution by 1 K is 4.2 J. Assume that no heat is exchanged with the surroundings.

 

NH3 + aq = NH3 aq + 34.2kJ

CO(NH2)2 + aq = CO(NH2)2aq - 14.4kJ


Question (5): In the reactions underlined in sections 1 and 2, how does the catalyst increase the reaction speed and promote the reaction? Describe the mechanism in 20using 151515 words or fewer.


Chemistry Problem III

Problem III-l. Read the following text and answer Questions (1)–(5).

 A Daniel cell, expressed as (–)Zn | ZnSO4 aq | CuSO4 aq | Cu(+), includes two units: one unit consists of a zinc plate and a zinc sulfate (ZnSO4) solution, and another unit consists of a copper plate and a copper sulfate(II) (CuSO4) solution. The two units are separated by a plate, such as an unglazed plate.

In general, as shown in the following figure, a cell can be constructed by connecting two units (Units A and B), each containing a metal plate immersed in an electrolyte solution, through a salt bridge. A salt bridge is a tube in which a salt solution, such as potassium chloride (KCl), is stabilized in solidified agar to permit ions to flow under a potential field applied between the two solutions. This cell can be used to determine the tendency of a metal to ionize. In a cell comprising two types of metal plate, the unit containing the more easily ionized plate acts as the negative electrode.

Question (1): Express the cell half reactions and overall reaction occurring in a Daniel cell during discharge.

Question (2): If a Daniel cell is permitted to discharge 965 C, what is the magnitude of the change in mass of the Zn plate? Provide answers (in g) with two significant figures, and use + to indicate an increase and – to indicate a decrease.

Question (3): In cell (a) described in the following table, electric current flows from Unit B to Unit A. In 15 words or fewer, describe what happens at the surface of the metal in Unit B as the cell discharges.

Question (4): One of the cells (b)–(f) features a combination of units that would not permit an electric current to flow continuously. Identify this combination, write the corresponding symbol, and briefly describe why the combination is inappropriate for producing current.

Question (5): The cell (g) comprises Unit A, containing a potassium iodide (KI) solution and a platinum plate, and Unit B, containing a potassium permanganate (KMnO4)/sulfuric acid solution and a platinum plate. The cell is permitted to discharge. Express the respective reactions occurring at the negative and positive electrodes in terms of the half reactions. Include the electrons as e.

Table. Combination of units


UnitA UnitB
Symbol Metal Dissolved substance in the solution Metal Dissolved substance in the solution
(a) Al Aluminum sulfate Pt Sulfuric acid
(b) Al Aluminum sulfate Fe Iron sulfate(II)
(c) Al Ethanol Fe Iron sulfate(II)
(d) Fe Sulfuric acid Cu Copper sulfate(II)
(e) Fe Sulfuric acid Cu Sulfuric acid
(f) Pt Benzenesulfonic acid Fe Iron sulfate(II)
(g) Pt KI Pt KMnO4 and sulfuric acid



Problem III-2. Read the following text about a group 16 element (chalcogen) and its compounds, and answer Questions (1)–(4).

Note: All materials in the text are at 1 × 105 Pa and 25°C.

Material (a) is a colorless toxic gas that smells like rotten eggs and is present in hot spring water, volcanic gases, and the gas produced during protein putrefaction. Material (b) is a colorless toxic gas with an irritating odor and is produced during the combustion of a yellow solid (c). When (b) is injected into a solution containing (a), (c) is deposited. Here, (b) is slightly acidic in solution. 1When (b) is injected into hydrogen peroxide (H2O2), a solution containing (d) is produced. 2When a small metal chip is added to a solution containing (d), a gas, which can be collected by upward displacement, and a metal ion are produced.

The respective solutions of (a) and (d) can be used to examine metal ions.

Adding [ A ] to a solution containing (a) results in a precipitate; however, adding solutions containing [ B ], [ C ], or [ D ] to a solution containing (a) does not result in a precipitate. Adding [ B ] or [ C ] to a solution containing (d) results in a precipitate.

 

Question (1): Express the reaction equation described by the process underlined in section 1.

Question (2): Provide the oxidation numbers of each atom of the compounds present in (a), (c), and (d).

Question (3): Rather than reacting as described in the underlined section 2, (d) can react in an alternate way with a metal to produce a metal ion and a gas that can be collected by downward displacement. Suggest a metal that can be used in this alternate experiment, and describe the conditions under which this alternate reaction is favored.

Question (4): From the following list, select one metal ion most appropriate for each of the stages[ A ] –[ D ] in the text above. The ordering of [ B ] and [ C ] is not important.

Mg2+   Ca2+   Pb2+   Ba2+


Chemistry Problem IV

Read the following text and answer Questions (1)–(7).

Modern society is built on the utilization of numerous organic compounds produced by the petrochemical industry. Propene, 1a hydrocarbon with one double bond produced during the thermal decomposition of oil, is important as an industrial raw material and can be converted into various compounds through a variety of addition reactions. 2The addition of water to the double bond of propene using acid catalysts produces compound (a). Oxidization of (a) produces compound (b). 3The reaction of (a) or (b) with a sodium hydroxide (NaOH) solution and iodine (I2) results in a yellow precipitate with a characteristic odor. Filtering and acidifying this precipitation yields acetic acid. The oxidation of compound (c) through the addition of benzene to propene, followed by dissolution in dilute sulfuric acid, yields compound (d), which is widely used as a resin material, along with (b) as a by-product. Propene is also important as a raw material for plastic production. If propene undergoes an addition self-polymerization reaction, it yields a thermoplastic resin, the polymer (e). The depletion of oil resources is becoming increasingly important, driving an urgent need to develop novel renewable materials that can replace these industrial raw materials to enable sustainable manufacturing, and can be incorporated into production processes.

 

Question (1): What are the hydrocarbons underlined in section 1 collectively called?

Question (2): Propene has a constitutional isomer. Draw the structural formula of the constitutional isomer.

Question (3): The reaction described in the underlined section 2 yields (a). In addition, this reaction could yield a constitutional isomer (f). Draw the structural formulae of these two compounds.

Question (4): Express the rational formula of compound (b). Express the chemical equation resulting from applying the reaction described in the underlined section 3 to (b).

Question (5): Write the compound names for (c) and (d).

Question (6): Draw the structural formula of polymer (e).

Question (7): Oxidation of propene in an acidic potassium permanganate (KMnO4) solution yields acetic acid and formic acid. This oxidation reaction can be used to synthesize adipic acid, a raw material used to prepare nylon 66 (6,6-nylon), from hydrocarbon (g) containing six carbons. Draw the structural formulae of adipic acid and (g).

 

Chemistry Problem V

Read the following text and answer Questions (1)–(6). Note: Use a dashed line to indicate a hydrogen bond.

 

Hydrogen fluoride (HF) 1displays a large polarity because the[ A ]of a fluorine atom is large and differs significantly from the[ A ]of a hydrogen atom.[ A ]positively charged hydrogen atom on one HF molecule is attracted to a negatively charged fluorine atom on another HF molecule via electrostatic forces. The stable attraction between a positively charged hydrogen atom in one molecule and an atom (such as F, O, or N, which has a large [ A ]) not directly bonded to the hydrogen atom via a covalent bond is referred to as a “hydrogen bond.” Water molecules (H2O) exhibit a high boiling point due to strong hydrogen bonds, despite the low molecular weight of water. 2Proteins form structures, such as α-helixes and β-sheets, via hydrogen bonds. These structure are called “[ B ]”, one of the higher-order structures of protein.

 

Question (1): Provide the most appropriate terms for [ A ] and [ B ].

Question (2): Draw the Lewis structures (electron dot diagrams) of H2O and carbon dioxide (CO2).

Question (3): H2O is a polar molecule, whereas CO2 is a non-polar molecule. This is because the shapes of H2O and CO2 molecules differ. Illustrate the differences in the shapes of H2O and CO2 molecules to clearly show this effect. Above each atom, indicate the partial charge using δ+ and δ–, following the example of HF, shown below.

example

Question (4): Benzoic acid forms a dimmer via hydrogen bonds. Draw the structural formula of this dimer.

Question (5): The structure of alanine, an amino acid present in proteins, is shown in the following figure. As mentioned in the underlined section 2, assume that this structure is related to the higher-order structure of proteins. Select those atomic groups (I–IV) in the following figure that are involved in the formation of hydrogen bonds. Illustrate a hydrogen bond that can form between two alanine moieties.


Figure. The structure of alanine in a protein


Question (6): In addition to peptide bonds and hydrogen bonds between amino acids, covalent bonds can form between two cysteine residues to stabilize higher-order structures in a protein. Provide the name of this covalent bond. Draw the structural formula of a glycine and cysteine dipeptide containing this covalent bond. Note: Amino acids take the form of R–CH(NH2)–COOH, where R is H in glycine and CH2SH in cysteine.

(End of the problems)