T5-3P2 [216 marks] H 2 (g) + I 2 (g) 2HI(g) K c. An example of a homogeneous reversible reaction is the reaction between hydrogen and iodine.

Transcription

1 T5-3P2 [216 marks] An example of a homogeneous reversible reaction is the reaction between hydrogen and iodine. H 2 (g) + I 2 (g) 2HI(g) 1a. Outline the characteristics of a homogeneous chemical system that is in a state of equilibrium. 1b. Deduce the expression for the equilibrium constant, K c. 1c. Predict what would happen to the position of equilibrium and the value of if the pressure is increased from 1 atm to 2 atm. K c

2 1d. The value of K c at 500 K is 160 and the value of K c at 700 K is 54. Deduce what this information tells us about the enthalpy change of the forward reaction. 1e. The reaction can be catalysed by adding platinum metal. State and explain what effect the addition of platinum would have on the value of the equilibrium constant. Propane can be formed by the hydrogenation of propene. CH 3 CH=CH 2 (g) + H 2 (g) CH 3 CH 2 CH 3 (g) 1f. State the conditions necessary for the hydrogenation reaction to occur.

3 1g. Enthalpy changes can be determined using average bond enthalpies. Define the term average bond enthalpy. 1h. Determine a value for the hydrogenation of propene using information from Table 10 of the Data Booklet. 1i. Explain why the enthalpy of hydrogenation of propene is an exothermic process. 1j. Describe a chemical test that could be used to distinguish between propane and propene. In each case state the result of the test.

4 1k. Under certain conditions propene can polymerize to form poly(propene). State the type of polymerization taking place and draw a section of the polymer to represent the repeating unit. 1l. Other than polymerization, state one reaction of alkenes which is of economic importance. Define the term average bond enthalpy. 2a.

5 The following equation represents a combustion reaction of propane, C 3 H 8 (g) when the oxygen supply is limited. 1 C 3 H 8 (g) + 3 O 2 (g) 3CO(g) + 4H 2 O(g) 2 (i) Determine ΔH, the enthalpy change of the reaction, in kj mol, using average bond enthalpy data from Table 10 of the 2b. 1 Data Booklet. The bond enthalpy for the carbon-oxygen bond in carbon monoxide, CO, is 1072 kj mol 1. [4 marks] (ii) The CO molecule has dative covalent bonding. Identify a nitrogen-containing positive ion which also has this type of bonding. Analytical techniques are very useful in determining molecular structures. A compound, X, has the empirical formula C 2 H 4 O. 3a. Identify the analytical technique that would most readily provide the additional data required to calculate the molecular formula of X.

6 The molecular formula of X is C 4 H 8 O 2. The information in the IR spectrum below can be used to help determine the structure of X. 3b. (i) State what information about a molecule can be obtained from its IR spectrum. (ii) Deduce the information obtained from absorptions A and B. [4 marks] A: B: (iii) Comment on the absence of any major absorption in the region cm 1.

7 The 1 H NMR spectrum of X shows three peaks with relative areas of 2:1:1. (i) 3c. Deduce what information can be obtained from these data. [4 marks] (ii) Deduce the structure of X. A potato chip (crisp) was ignited and the flame was used to heat a test tube containing water. 3d. (i) Calculate the heat required, in kj, to raise the temperature of the water, using data in the table above and from Table 2 of the [3 marks] Data Booklet. (ii) Determine the enthalpy of combustion of the potato chip, in kj g 1.

8 3e. This energy comes mainly from the combustion of triglycerides. State the name of one other type of lipid found in the body and one role, other than energy storage, of this type of lipid. Name: Role: 3f. Explain why lipids have a higher energy content than carbohydrates. The straight chain form of glucose is represented below. 3g. Glucose is mainly present in one of two cyclic forms: α-glucose and β-glucose. Distinguish between the two cyclic forms by completing the diagrams below. Fructose is an isomer of glucose, but they differ with regard to one functional group and hence in their redox properties. 3h. (i) Identify the functional group present in glucose, but not fructose. [3 marks] (ii) Identify the functional group present in fructose, but not glucose. (iii) Identify the sugar that acts as a reducing agent.

9 3i. Outline how the structure of cellulose is related to that of glucose. Macronutrients and micronutrients are essential components of a balanced diet. 3j. State the difference between macronutrients and micronutrients. Aluminium and iron are both widely used in modern society. 3k. Almost all iron is used in the form of an alloy. State the name of the most common type of iron alloy and the other element that is an essential component of these alloys. Name: Other element: 3l. An early alloy of aluminium was Duralumin which contained small quantities of copper and magnesium. This is stronger and more rigid than pure aluminium. Explain on an atomic level why the addition of other elements has this effect.

10 Fuel cells and rechargeable batteries are both convenient ways of providing portable electric power. 3m. Compare fuel cells and rechargeable batteries giving one similarity and one difference. Similarity: Difference: 3n. One common type of rechargeable cell is the nickel cadmium (NiCad) battery. For each terminal of this battery state the initial and [3 marks] final oxidation number of the element when the cell is delivering a current. Hence deduce which electrode is acting as the anode and which the cathode. 3o. A common type of fuel cell uses hydrogen and oxygen with an acidic electrolyte. State the half-equations for the reactions at the two electrodes. Positive electrode: Negative electrode: 3p. The electrodes of fuel cells and rechargeable batteries have a feature in common with heterogeneous catalysts. Identify this feature and state why it is important for them to work efficiently.

11 Petroleum (mineral oil) can be used either as a fuel or a chemical feedstock. 3q. Name two fuels that are obtained from petroleum. 3r. Describe one environmental problem that can result from the combustion of these fuels in the internal combustion engine and identify the specific combustion product responsible. 3s. Plastic litter is an environmental problem that results from the use of petroleum as a chemical feedstock. Identify the property of plastics that is responsible for this. 3t. One product that is made from crude oil is the chemical feedstock that can be used to synthesize commercial liquid-crystal displays. Discuss the properties that a substance must have to make it suitable for use as a liquid-crystal display.

12 Drugs are most commonly taken orally. 3u. Drugs are most commonly taken orally. (a) State one advantage and one disadvantage of this. Advantage: Disadvantage: 3v. List three methods, other than orally, that can be used for the administration of a drug. Many diseases are the result of infection of the body by either bacteria or viruses. 3w. (i) State the name of one disease caused by each. Bacteria: [5 marks] Viruses: (ii) Discuss the differences between bacteria and viruses.

13 3x. Describe two misuses of antibiotics that have led to some bacteria becoming resistant. 3y. It is much more difficult to produce effective antiviral drugs than drugs that kill bacteria. Describe two ways in which antiviral drugs work. The temperature of the Earth s surface is currently increasing. Many scientists attribute this to an increase in the levels of greenhouse gases in the atmosphere as a result of human activity. 3z. Explain how the interaction of greenhouse gases in the atmosphere with radiation could lead to an increase in the temperature of the Earth s surface. [3 marks]

14 Suggest why carbon dioxide is the greenhouse gas most frequently connected with the effect of human activity. 3aa. 3ab. Other than carbon dioxide and water, identify one other greenhouse gas and state its source. One major environmental problem that affects many countries is acid rain. Explain, writing an appropriate equation, why, even in an unpolluted environment, rainwater is still slightly acidic. 3ac.

15 Nitrogen monoxide pollution is a major contributor of acid rain. (i) 3ad. (ii) (iii) Outline the major source of this gas, including an equation. Describe, including an equation, a chemical method used to control the emission of this pollutant. Identify a compound, to which nitrogen monoxide is eventually converted, that is responsible for acidity in lakes and rivers. [5 marks] Most foods are complex mixtures and many components of them are nutrients. Identify the types of nutrients A, B and C. 3ae. [3 marks] A B C

16 3af. State the names of two types of nutrient other than those shown in part (b). Rancidity limits the shelf life of foods containing oils and fats. Rancidity can occur as a result of two separate processes. State these processes and explain the difference between them. 3ag. [3 marks] The structure of benzene originally described by August Kekulé is shown below. 3ah. Explain, giving two different pieces of evidence, why this is not a valid structure for the bonding in benzene.

17 Analytical techniques are very useful in determining molecular structures. A compound, X, has the empirical formula C 2 H 4 O. Peaks in a 1H NMR spectrum are measured relative to a reference standard. State the name of a substance used and identify 4a. one property that makes it particularly suitable for this application. A large proportion of the food we eat provides energy through the process of respiration. Carbohydrates and triglycerides are the food groups mainly responsible for providing this energy. 4b. Compare the behaviour of enzymes and inorganic catalysts, including reference to the mechanism of enzyme action and the ways in which this can be inhibited. [5 marks]

18 Polymers can be classified as addition polymers or condensation polymers. 4c. Outline the difference in the way in which polymerization occurs, stating a specific example of a polymer produced by each process. [5 marks] 4d. Polymers can either soften when heated or remain rigid until they decompose or combust. Other than Kevlar, state the names of one polymer that softens and one that does not. Explain this difference on a molecular level. [3 marks] Softening polymer: Non-softening polymer: Explanation:

19 Kevlar behaves as a lyotropic liquid crystal when dissolved in suitable solvents. Its structure is shown below. State the properties that a molecule, such as Kevlar, must have in order to enable it to behave as a liquid crystal. 4e. 4f. Discuss the additional properties that a substance must have to make it suitable for commercial liquid-crystal displays. 4g. Explain what is meant by the term lyotropic.

20 Alcohol abuse is a major problem in many countries, especially when associated with driving. Many police forces now use instruments that detect the presence of ethanol on a person s breath by its absorption of electromagnetic radiation. Identify the region of the electromagnetic spectrum used to detect the presence of ethanol. 4h. Many diseases are the result of infection of the body by either bacteria or viruses. 4i. Identify the particular structural feature of penicillins that is responsible for their action and explain how this prevents bacteria multiplying. [4 marks] 4j. The action of a drug molecule often depends on its shape. Discuss a specific example of a drug where one stereoisomer has a different physiological activity to the other.

21 Ozone is a gas present in both the stratosphere and the troposphere. 4k. Oxygen absorbs much of the ultraviolet (UV) radiation from the sun, but ozone is important because it absorbs UV radiation not absorbed by oxygen. Explain, referring to the bonding in the two molecules, why this is the case. [3 marks] 5a. Another structural isomer of C 4 H 9 Br is 2-bromo-2-methylpropane. Deduce the number of peaks and the splitting pattern in the 1H NMR spectrum of this isomer. Number of peaks: Splitting pattern: Transition metal complexes are coloured because electronic transitions occur within split d orbital energy levels. Identify two 5b. different factors that affect the colour of complexes of a specific transition metal.

22 5c. Phenolphthalein indicator is colourless in solutions with a ph less than 8.2 but pink in solutions with a ph greater than The molecule dissociates according to the equation: [3 marks] Explain, in terms of the structures, why the indicator is colourless at ph < 8.2 and is pink at ph > d. State and explain how the rate of an enzyme-catalysed reaction is related to the substrate concentration. [3 marks]

23 When an inhibitor is added it decreases the rate of an enzyme-catalysed reaction. State the effect that competitive and noncompetitive inhibitors have on the value of V max. Explain this in terms of where the inhibitor binds to the 5e. enzyme. [4 marks] Competitive inhibitor: Non-competitive inhibitor: 5f. (i) Sketch a graph to show the effect that a change in ph will have on the rate of an enzyme-catalysed reaction. [3 marks] (ii) Explain why changing the ph affects the catalytic ability of enzymes.

24 Lead acid batteries are heavy. Much lighter rechargeable cells are nickel cadmium batteries used in electronic equipment. 5g. Other than their chemical composition, discuss two major differences between fuel cells and nickel cadmium cells. 5h. Distinguish between thermotropic liquid crystals and lyotropic liquid crystals. Thermotropic: Lyotropic:

25 5i. Two substances that can be used in liquid crystals are commonly called PAA (4-azoxydianisole) and 5CB (4-pentyl-4'- cyanobiphenyl). [3 marks] Discuss on the molecular level three different factors that explain their liquid-crystal properties.

26 5j. Explain the workings of liquid crystals made up of compounds such as 5CB in liquid-crystal displays. [5 marks] The discovery of penicillin by Alexander Fleming in 1928 is often given as an example of serendipity in science. Describe what happens to bacteria when they come into contact with penicillin. 5k.

27 The structure of a particular type of penicillin called dicloxacillin is shown below. 5l. (i) (ii) Identify the β-lactam ring by drawing a circle around it. Explain why the β-lactam ring is so important in the mechanism of the action [5 marks] of penicillin. (iii) State the name of the functional group in dicloxacillin, circled below.

28 Comment on the fact that many bacteria are now resistant to penicillins. 5m. 5n. Explain, in terms of their bonding, how the presence of oxygen and ozone in the ozone layer helps to prevent both higher and lower energy UV light from reaching the surface of the Earth. [3 marks] 6. Which processes are exothermic? I. II. III. CH 3 CH 2 CH 3 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(g) Cl 2 (g) 2Cl(g) CH 3 CH 2 COOH(aq) + NaOH(aq) CH 3 CH 2 COONa(aq) + H 2 O(l) A. I and II only B. I and III only C. II and III only D. I, II and III 7. Which processes are exothermic? I. CH 3 CH 2 CH 3 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(g) II. Cl 2 (g) 2Cl(g) III. CH 3 CH 2 COOH(aq) + NaOH(aq) CH 3 CH 2 COONa(aq) + H 2 O(l) A. I and II only B. I and III only C. II and III only D. I, II and III

29 8. Which statement is correct for the enthalpy level diagram shown? A. The reaction is exothermic and the products are more stable than the reactants. B. The reaction is exothermic and the sign of the enthalpy change is positive. C. The reaction is endothermic and the sign of the enthalpy change is negative. D. The reaction is endothermic and the products are more stable than the reactants. 9. Which combination is correct about the energy changes during bond breaking and bond formation? 10. The reaction between methane and oxygen is exothermic. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) Which statement is correct? A. The total bond enthalpies of the reactants are less than the total bond enthalpies of the products. B. The total bond enthalpies of the reactants are greater than the total bond enthalpies of the products. C. The total energy released during bond formation is less than the total energy absorbed during bond breaking. D. The activation energy is the difference between the total bond enthalpies of the products and the total bond enthalpies of the reactants. In December 2010, researchers in Sweden announced the synthesis of N,N dinitronitramide, N(NO 2 ) 3. They speculated that this compound, more commonly called trinitramide, may have significant potential as an environmentally friendly rocket fuel oxidant. Methanol reacts with trinitramide to form nitrogen, carbon dioxide and water. Deduce the coefficients required to balance the 11a. equation for this reaction. N(NO 2 ) 3 (g)+ CH 3 OH(l) N 2 (g)+ CO 2 (g)+ H 2 O(l)

30 Calculate the enthalpy change, in kj mol 1, when one mole of trinitramide decomposes to its elements, using bond enthalpy data [3 marks] 11b. from Table 10 of the Data Booklet. Assume that all the N O bonds in this molecule have a bond enthalpy of 305 kj mol 1. 11c. Outline how the length of the N N bond in trinitramide compares with the N N bond in nitrogen gas, N 2.

31 11d. Deduce the N N N bond angle in trinitramide and explain your reasoning. [3 marks] Predict, with an explanation, the polarity of the trinitramide molecule. 11e.

32 Methanol can also be burnt as a fuel. Describe an experiment that would allow the molar enthalpy change of combustion to be 11f. calculated from the results. [3 marks] Explain how the results of this experiment could be used to calculate the molar enthalpy change of combustion of methanol. 11g. [3 marks]

33 Predict, with an explanation, how the result obtained would compare with the value in Table 12 of the Data Booklet. 11h. In December 2010, researchers in Sweden announced the synthesis of N,N dinitronitramide, N(NO 2 ) 3. They speculated that this compound, more commonly called trinitramide, may have significant potential as an environmentally friendly rocket fuel oxidant. Methanol reacts with trinitramide to form nitrogen, carbon dioxide and water. Deduce the coefficients required to balance the 12a. equation for this reaction. N(NO 2 ) 3 (g)+ CH 3 OH(l) N 2 (g)+ CO 2 (g)+ H 2 O(l) Calculate the enthalpy change, in kj mol 1, when one mole of trinitramide decomposes to its elements, using bond enthalpy data [3 marks] 12b. from Table 10 of the Data Booklet. Assume that all the N O bonds in this molecule have a bond enthalpy of 305 kj mol 1. The entropy change, ΔS, for the decomposition of trinitramide has been estimated as +700 JK. Comment on the sign of 12c. 1 mol 1 ΔS.

34 Using +700 JK as the value for the entropy change, along with your answer to part (c), calculate, in, for [3 marks] 12d. 1 mol 1 ΔG kj mol 1 this reaction at 300 K. (If you did not obtain an answer for part (c), then use the value 1000 kj mol 1, but this is not the correct value.) Explain how changing the temperature will affect whether or not the decomposition of trinitramide is spontaneous. 12e. 12f. Outline how the length of the N N bond in trinitramide compares with the N N bond in nitrogen gas, N 2.

35 Deduce the N N N bond angle in trinitramide and explain your reasoning. 12g. [3 marks] Predict, with an explanation, the polarity of the trinitramide molecule. 12h. International Baccalaureate Organization 2017 International Baccalaureate - Baccalauréat International - Bachillerato Internacional Printed for BLUPS