production of nitric acid

production of nitric acid unit four – 2014 – chemistry © The School For Excellence 2014 Unit 4 Chemistry – The Production of Nitric Acid Page 1 THE PRODUCTION OF NITRIC ACID (HNO3) USES OF NITRIC ACID In terms of production, nitric acid is the third most widely produced acid across the world. It has a wide range of uses in agriculture, industry and medicine where it is used as a fertiliser and in the manufacture of fireworks, explosives, medicines, dyes, food preservatives, pesticides and detergents. PROPERTIES OF NITRIC ACID Nitric acid: • Is colourless in its pure form but may become orange or reddish in colour if contaminated by nitrogen oxides. • Is highly corrosive. • Is a poisonous liquid (freezing point -42˚C, boiling point 83˚C). • Reacts with water or steam to produce heat and toxic, corrosive and flammable vapours. • Can cause severe burns. • Miscible in water at all concentrations. • Has an acid dissociation constant (pKa) of −1.4. In aqueous solution, it almost completely (93% at 0.1 mol/L). • Will decompose at higher temperatures to form nitrogen oxides. Nitric acid is both a strong monoprotic acid and a strong oxidant, particularly when hot and concentrated. © The School For Excellence 2014 Unit 4 Chemistry – The Production of Nitric Acid Page 2 OXIDISING PROPERTIES The products of the reaction between nitric acid and metals depends upon the reactivity of the metal and the concentration of the acid. As a general rule, oxidising reactions occur primarily with the concentrated acid, favouring the formation of nitrogen dioxide (NO2). Reaction between a reactive metal and dilute acid (<_x0031_M_x0029_: _x0038__x0723__x0029__x0748__x0be6__x0029_ _x002b_ _x0033_0_x072a__x0731__x0730__x0b37__x0028__x0bd4__x0be4__x0029_ _x2192_ _x0038__x0723__x0731__x0730__x0029__x0748__x0b37__x0029__x0b36__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0033__x0730__x072a__x0b38__x0730__x0731__x0b37__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0039__x072a__x0b36__x0731__x0028__x0bdf__x0029_ Nitrogen has been reduced from _x002b_5 all the way to _x002d_3. Reaction between a less reactive metal and more concentrated acid: _x2022_ Acid concentration _x0033_ to _x0036_M: _x0033__x0751__x0725__x0029__x0be6__x0029_ _x002b_ _x0038__x072a__x0731__x0730__x0b37__x0028__x0bd4__x0be4__x0029_ _x2192_ _x0033__x0751__x0725__x0731__x0730__x0029__x0b37__x0029__x0b36__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0034__x072a__x0b36__x0731__x0028__x0bdf__x0029_ _x002b_ _x0032__x0730__x0731__x0028__x0bda__x0029_ Nitrogen has been reduced from _x002b_5 to _x002b_2. _x2022_ Acid concentration _x0031_2M: _x0751__x0725__x0029__x0be6__x0029_ _x002b_ _x0034__x072a__x0731__x0730__x0b37__x0028__x0bd4__x0be4__x0029_ _x2192_ _x0751__x0725__x0731__x0730__x0029__x0b37__x0029__x0b36__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0032__x072a__x0b36__x0731__x0028__x0bdf__x0029_ _x002b_ _x0032__x0730__x0731__x0b36__x0028__x0bda__x0029_ Nitrogen has been reduced from _x002b_5 to _x002b_4. Since nitric acid is an oxidising agent_x002c_ hydrogen _x0028_H2_x0029_ is rarely formed. Only magnesium _x0028_Mg_x0029__x002c_ manganese _x0028_Mn_x0029_ and calcium _x0028_Ca_x0029_ react with cold_x002c_ dilute nitric acid to give hydrogen: Mg_x0028_s_x0029_ _x002b_ _x0032_ HNO3_x0028_aq_x0029_ _x2192_ Mg_x0028_NO3_x0029_2_x0028_aq_x0029_ _x002b_ H2_x0028_g_x0029_ Reaction with non-metallic elements _x0028_with the exceptions of nitrogen_x002c_ oxygen_x002c_ noble gases_x002c_ silicon and halogens_x0029_ usually oxidises them to their highest oxidation states. The formation of nitrogen dioxide occurs for concentrated acid and nitric oxide for dilute acid. C_x0028_s_x0029_ _x002b_ _x0034_ HNO3_x0028_aq_x0029_ _x2192_ CO2_x0028_g_x0029_ _x002b_ _x0034_ NO2_x0028_g_x0029_ _x002b_ _x0032_ H2O_x0028_l_x0029_ _x0033_ C_x0028_s_x0029_ _x002b_ _x0034_ HNO3_x0028_aq_x0029_ _x2192_ _x0033_ CO2_x0028_aq_x0029_ _x002b_ _x0034_ NO_x0028_q_x0029_ _x002b_ _x0032_ H2O_x0028_l_x0029_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0033_ ACIDIC PROPERTIES Nitric acid is a strong acid. In moderately dilute solution _x0028__x007e_ _x0030_.1 M_x0029_ it is dissociated to an extent of about _x0039_3_x0025__x002c_ in accordance with the reaction_x002c_ Being an acid_x002c_ it reacts with alkalies to from nitrates It decomposes carbonates and bicarbonates as: _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0034_ THE PRODUCTION OF NITRIC ACID Nitric acid is made from ammonia in a three-step process known as the Ostwald process. Step _x0031_: Oxidation of NH3 to NO _x002e_ Step _x0032_: Oxidation of NO to NO2 _x002e_ Step _x0033_: Absorption and reaction of NO2 with water. STEP _x0031_: CATALYTIC OXIDATION OF AMMONIA Air is preheated and mixed with ammonia _x0028_which is not preheated as it would decompose_x0029_ and then passed through a converter where the following reaction occurs: _x0031_ _x0033__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0035_ _x0034_ _x0036_ _x0039_07 NH O NO H O H kJmol gg g g _x2212_ _x002b_ _x2192_ _x002b_ _x0394_="−" In this reaction_x002c_ ammonia undergoes catalytic oxidation to form nitrogen monoxide _x0028_nitric oxide _x0028_NO_x0029_ and water. This is the start of the oxidation process. The nitrogen in ammonia starts with an oxidation number of _x002d_3 _x0028_its lowest possible oxidation state_x0029_ and is converted to _x002b_2 in nitrogen monoxide. The ratio of air _x002f_ammonia must be carefully monitored and is maintain at between _x0039_ and _x0031_2_x0025_. If the concentration of ammonia rises much beyond this_x002c_ the mixture becomes explosive. The catalyst used in this process is _x0039_0_x0025_ platinum alloyed with _x0031_0_x0025_ rhodium for increased strength. The catalyst consists of several woven or knitted gauzes formed from the alloy. The gauze mats are preheated so that the gases are directly heated as they pass over the catalyst. The catalyst may become poisoned by air pollution and contamination from the ammonia which reduces its efficiency. The cost of these catalysts are extremely high and need to be frequently replaced due to the wear and tear they experience under such severe conditions. A cheaper alternative is yet to be developed. NO2 _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0035_ Nitrous oxide_x002c_ nitrogen and water are also simultaneously formed in this step_x002c_ as shown below. _x0031_ _x0033__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0033_ _x0032_ _x0036_ _x0031_267 NH O N H O H kJmol gg g g _x2212_ _x002b_ _x2192_ _x002b_ _x0394_="−" _x0033__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0032_2 _x0033_ NH O N O H O gg g g _x002b__x2192_ _x002b_ Conditions are carefully controlled in the converter in order to ensure that nitrogen monoxide _x0028_NO_x0029_ is the main product_x002c_ rather than nitrogen gas _x0028_N2_x0029_ or nitrogen _x0028_I_x0029_ oxide _x0028_ N O2 _x0029_. The yield of nitric oxide depends on the pressure and temperature as shown below. Pressure _x0028_atm_x0029_ Temperature _x0028__x02da_C_x0029_ NO yield _x0028__x0025__x0029_ Below _x0031_.7 _x0038_10-850 _x0039_7 _x0031_.7-6.5 _x0038_50-900 _x0039_6 Above _x0036_.5 _x0039_00-940 _x0039_5 Typical conditions for the production of NO are therefore: _x2022_ High temperatures _x0028_820 _x0039_30o _x2212_ C _x0029_ _x2022_ High pressures _x0028_11 atm_x0029_ Temperature Considerations Even though higher yields would be obtained at lower temperatures _x0028_the forward reaction is exothermic_x0029__x002c_ the process is carried out at high temperatures _x0028_820 _x0039_30o _x2212_ C _x0029_. This is because the rate at which the reaction proceeds at low temperatures is too slow to be commercially viable. To compensate for the resultant loss in product yield_x002c_ the gas mixture is passed over a catalyst a number of times to produce a moderate yield of NO _x002e_ Pressure Considerations At the high temperatures employed_x002c_ the NO formed decomposes to form nitrogen and oxygen. _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_NO N O g _x0083_ g g _x002b_ To avoid this_x002c_ the gas mixture is passed across the catalyst very rapidly _x0028_contact time is approximately _x0030_.003 sec_x0029_. To achieve this high flow rate_x002c_ the reaction is performed at high pressures even though lower pressures would result in a higher product yield. The consequential loss in yield of NO is compensated for by the increased reaction rates and the quality of product obtained. Note: Even with all the compromises that are required in this step_x002c_ the yield of NO is in the order of _x0039_5_x0025_. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0036_ STEP _x0032_: OXIDATION OF NITROGEN MONOXIDE The waste heat from the gases leaving the converter is recycled and used in other sections of the plant. The temperature of the nitrogen monoxide mixture is reduced to around _x0032_00-250_x02da_C in this process. The gases are then passed through a cooling chamber and their temperature reduced to approximately _x0035_0_x02da_C. Any condensed water is transferred to the absorption tower. As the gases are cooled_x002c_ the nitrogen monoxide oxidises to nitrogen dioxide _x0028_the nitrogen in NO is oxidised from _x002b_2 to _x002b_4 in the nitrogen dioxide_x0029_. The oxygen consumed in this step may be added from an external source or is provided by excess oxygen in the gaseous mixture exiting the converter. The reaction is: _x0031_ _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0032_ _x0031_14 NO O NO H kJmol gg g _x2212_ _x002b_ _x0394_="−" _x0083_ Temperature Considerations As this reaction is exothermic_x002c_ high yields of product can be achieved by using lower temperatures. This reaction is unusual in that its rate increases with decreasing temperature meaning that NO CONFLICT arises between the conditions required to optimise rates and yields. Pressure Considerations Yields can be further maximised by using high pressures. The system will respond to high pressures by favouring the reaction that will produce the fewer mole of gas _x2013_ which in this case is the formation of products. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0037_ STEP _x0033_: ABSORPTION OF NITROGEN DIOXIDE Water is mixed with the nitrogen dioxide gas in absorption towers to form dilute solutions of nitric acid according to the following overall reaction: _x0032__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0033_ _x0032_ NO H O HNO NO g _x002b__x2192_ _x002b_ l aq g This is a redox reaction in which produces nitrogen in its highest oxidation state _x0028__x002b_5 in nitric acid_x0029_. The towers contain large number of inert plates packed with inert granular materials designed to increase the contact between the gases and water. This reaction is exothermic and continuous cooling is needed. The conversion is favoured by low temperatures and significant reaction occurs until the gases leave the towers. Nitrogen dioxide gas is pumped at _x0035_ to _x0031_0 atm across the inert packing material_x002c_ through which water is trickled from above. Reaction between the water and the gas produces nitric acid_x002c_ which then dissolves in the remaining water. Small quantities of NO are also produced_x002c_ which reacts with oxygen from the air in the tower to produce NO2 which then reacts as before. A solution of nitric acid may be produced that is about _x0034_5_x2013_60_x0025_ HNO3 _x002e_ This can easily be increased to _x0036_8_x0025_ _x0028_equivalent to _x0031_6 M _x0029_ by distilling off some of the water. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0038_ WASTES AND MANAGEMENT _x2022_ The Ostwald process is very energy efficient and produces little waste. _x2022_ The oxidation of ammonia is highly exothermic_x002c_ generating sufficient heat energy to meet the energy needs of the rest of the plant. _x2022_ The main gaseous emissions from the Ostwald process include NO and NO2 _x002e_ Both gases contribute to photochemical smog_x002c_ and therefore_x002c_ careful attention must be paid to minimising how much of these gases are emitted into the atmosphere. One approach involves the heating of these gases using a fuel such as natural gas_x002c_ naphtha or hydrogen_x002c_ over a catalyst_x002c_ so that the NOx is reduced to N2 _x002e_ CH4_x0028_g_x0029_ _x002b_ _x0034_NO2_x0028_g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ _x0032_H2O_x0028_l_x0029_ _x002b_ _x0034_NO_x0028_g_x0029_ then_x002c_ CH4_x0028_g_x0029_ _x002b_ _x0034_NO g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ _x0032_H2O_x0028_l_x0029_ _x002b_ _x0034_N2_x0028_g_x0029_ Also: CH4_x0028_g_x0029_ _x002b_ _x0034_N2O g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ _x0032_H2O_x0028_l_x0029_ _x002b_ _x0032_N2_x0028_g_x0029_ H2_x0028_g_x0029_ _x002b_ NO2_x0028_g_x0029_ _x00e0_ _x0032_H2O_x0028_l_x0029_ _x002b_ NO_x0028_g_x0029_ then_x002c_ _x0032_H2_x0028_g_x0029_ _x002b_ _x0032_NO_x0028_g_x0029_ _x00e0_ _x0032_H2O_x0028_l_x0029_ _x002b_ N2_x0028_g_x0029_ Also: H2_x0028_g_x0029_ _x002b_ N2O g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ H2O_x0028_l_x0029_ _x002b_ _x0032_N2_x0028_g_x0029_ In addition_x002c_ the absorption tower may be modified by increasing its size or operating pressure so as to maximise conversion of NOx to nitric acid. _x2022_ The gas mixture entering the converter is filtered to remove catalytic poisons_x002c_ which increases the efficiency of the catalysts and hence decreasing the pressure _x0028_and energy_x0029_ required to force the gas through the catalyst bed. _x2022_ Heat exchangers are employed to remove heat released by the reaction in the converter and then using it to heat incoming gases or generate electricity. _x2022_ At the high temperatures and pressures used in the converter_x002c_ the catalyst slowly vaporises and is lost. Gases leaving the converter are passed through a filter to recover the metals and minimise the impact of these vapours on the environment. _x2022_ Specific catalysts are added to the converter to decompose any N O2 formed. Note: Nitrogen_x0028_I_x0029_ oxide is a significant greenhouse gas. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0039_ HEALTH AND SAFETY _x2022_ Concentrated nitric acid is corrosive and causes severe burns to the skin and eyes. Its fumes evolve nitrogen dioxide gas which at low concentrations may cause lung oedema _x0028_fluid in the lungs_x0029_ and fatal with excessive exposure. _x2022_ As a strong oxidant_x002c_ nitric acid reacts readily with a range of organic materials and metals to produce flammable and _x002f_or explosive products. _x2022_ NOx gases are significant greenhouse gases and some can react with water to form acid rain. Safety Measures Employed: _x2022_ There is careful monitoring in nitric acid plants for leaks and spills and all employees are trained to handle such if they do occur. _x2022_ Equipment must be carefully maintained to avoid corrosion. _x2022_ Acid spills are contained using materials such as earth_x002c_ clay or sand_x002c_ and then neutralised with a base such as slaked lime _x0028_Ca_x0028_ OH _x0029_2 _x0029_ or sodium carbonate. _x2022_ Full protective equipment and breathing apparatus is readily accessible across the plant. _x2022_ The ratio of ammonia to air in the gas entering the converter is continuously measured and controlled to ensure it does not reach explosive conditions. _x2022_ Un-reacted gases are recycled where possible. _x2022_ Various methods are employed to limit NOx emissions_x002c_ maximise conversion efficiency_x002c_ and minimise loss of energy. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_0 MIXED QUESTIONS QUESTION _x0031_ A number of different oxidation states of nitrogen are involved in the industrial production of nitric acid from ammonia. State the various nitrogen containing compounds involved in the Ostwald Process and the corresponding oxidation states of nitrogen. Solution QUESTION _x0032_ Describe the theoretical conditions that should be used to maximise the rate of the reaction of ammonia and oxygen to produce nitrogen monoxide. Are these the conditions actually used_x003f_ If not_x002c_ why not_x003f_ Solution _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_1 QUESTION _x0033_ Which of the following is not a property of nitric acid_x003f_ A It is monoprotic. B It is a strong acid. C It is a good oxidant. D It forms nitride salts. QUESTION _x0034_ Write equations for the following reactions of nitric acid: _x0028_a_x0029_ With water. _x0028_b_x0029_ With ammonia to make ammonium nitrate. _x0028_c_x0029_ With potassium hydroxide to make potassium nitrate. _x0028_d_x0029_ With zinc metal to form zinc ions and ammonia. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_2 QUESTION _x0035_ During the Ostwald process_x002c_ nitrogen monoxide is made from ammonia at about _x0039_00_x00b0_C and then cooled to _x0033_0_x00b0_C before being reacted with air to make nitrogen_x0028_IV_x0029_ oxide. Both these reactions are exothermic. Why are the temperatures used for these reactions so different_x003f_ Solution QUESTION _x0036_ As the gas passes through the catalyst bed in the converter during nitric acid manufacture_x002c_ its temperature increases. The gas must be cooled before it is mixed with air. _x0028_a_x0029_ Why does the temperature of the gas rise_x003f_ _x0028_b_x0029_ Why is it necessary to cool the gas_x003f_ _x0028_c_x0029_ What side benefit is obtained from the need to cool gases_x003f_ Solution _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_3 QUESTION _x0037_ The flow chart below shows the processes leasing to the production of nitric acid on an industrial scale. _x0028_i_x0029_ What is Gas A_x003f_ What is Gas B_x003f_ _x0028_ii_x0029_ Write an equation for the process occurring in Reactor _x0031_. _x0028_iii_x0029_ What would be the effect of increasing the temperature in Reactor _x0031_ on the rate of production of gas B_x003f_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_4 _x0028_iv_x0029_ What would be the effect of increasing the temperature in Reactor _x0031_ on the equilibrium yield of gas B_x003f_ _x0028_v_x0029_ What is the function of the catalyst in Reactor _x0032__x003f_ _x0028_vi_x0029_ At low temperatures_x002c_ NO2 is in equilibrium with another oxide of nitrogen. Write an equation for this equilibrium. _x0028_vii_x0029_ What is reagent D_x002c_ which is added into Reactor _x0034_ with NO2 _x003f_ Write an equation for the reaction occurring in Reactor _x0034_. _x0028_viii_x0029_ Reagent E is recycled back into the cooling tower as shown in the diagram. What is reagent F_x003f_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_5 QUESTION _x0038_ Nitrogen oxide_x002c_ NO_x002c_ is a small but important component of the atmosphere and is produced commercially on a large scale during the manufacture of nitric acid. _x0028_i_x0029_ Name two processes_x002c_ one natural and one involving the activities of man_x002c_ that contribute significant significantly to the NO present in the atmosphere. _x0028_ii_x0029_ Write a balanced equation for the reaction by which NO is formed during the production of nitric acid by the Ostwald process. _x0028_iii_x0029_ NO produced during the Ostwald process is oxidised to NO2 _x002c_ according to the equation _x0031_ _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0032_ _x0031_81 NO O NO H kJmol gg g _x2212_ _x002b_ _x2192_ _x0394_="−" _x002e_ In a particular factory_x002c_ energy is released at a rate of _x0035_70 kJ per minute during this stage. What volume of NO2 at STP is being released each minute_x003f_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_6 QUESTION _x0039_ _x0028_a_x0029_ Calculate the atom economy of ethylene oxide_x002c_ created in the following reaction: _x0028_b_x0029_ Would this method of production of ethylene oxide be considered as a _x201c_Green_x201d_ process_x003f_ Give a reason for your answer. _x0028_c_x0029_ Recently_x002c_ a method of synthesising ethylene oxide from ethene and oxygen using a silver catalyst was developed. What_x2019_s the atom economy of this alternative reaction_x003f_ SOLUTIONS _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_ FOR ERRORS AND UPDATES_x002c_ PLEASE VISIT WWW.TSFX.COM.AU _x002f_MC-UPDATES QUESTION _x0031_ The Ostwald process involves the oxidation of nitrogen_x002c_ through a series of steps_x002c_ from its lowest oxidation state to its highest. Starting with ammonia _x0028_ NH3 _x002d_ oxidation number of N="−3)," nitrogen monoxide _x0028_ NO _x002d_ oxidation number of N="+2" _x0029_ is formed_x002c_ followed by nitrogen dioxide _x0028_ NO2 _x002d_ oxidation number of N="+4" _x0029_ and finally nitric acid _x0028_ HNO3 _x002d_ oxidation number of N="+5)." QUESTION _x0032_ Refer to Notes. QUESTION _x0033_ Answer is D QUESTION _x0034_ _x0028_a_x0029_ HNO H O H O NO _x0033__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0033_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ aq l aq aq _x002b_ _x2212_ _x002b__x2192_ _x002b_ _x0028_b_x0029_ HNO NH NH NO _x0033__x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0034_ _x0033__x0028_ _x0029_ aq g aq _x002b_ _x2192_ _x0028_c_x0029_ HNO KOH H O KNO _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ aq aq l aq _x002b_ _x2192__x002b_ _x0028_d_x0029_ _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0038_4 _x0033_ Z s aq aq aq g l n HNO H Zn NH H O _x002b_ _x002b_ _x002b_ _x002b__x2192_ _x002b_ _x002b_ or _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0028_ _x0029_ _x0034__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0039_4 _x0033_ Z s aq aq aq g l n HNO H Zn NH H O _x002b_ _x002b__x002b_ _x002b_ _x002b__x2192_ _x002b_ _x002b_ QUESTION _x0035_ Stage _x0031_ of the Ostwald Process: The nitrogen monoxide produced in the converter is cooled to about _x0033_0o C to maximise the production of NO2 in the reaction below. _x0031_ _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0032_ _x0031_14 NO O NO H kJmol gg g _x2212_ _x002b_ _x0394_="−" _x0083_ As this reaction is exothermic_x002c_ high yields of product can be achieved by using lower temperatures. And as reaction rates for this system increase with decreasing temperature_x002c_ no conflicts are created between rates and yields. In Stage _x0032_ of the Ostwald Process_x002c_ the reaction once again is exothermic_x002c_ meaning that higher product yields will be obtained by using lower temperatures. In this case however_x002c_ the process is carried out at high temperatures _x0028_820 _x0039_30o _x2212_ C _x0029_ as the rate at which the reaction proceeds at low temperatures is too slow to be commercially viable. To compensate for the resultant loss in product yield_x002c_ the gas mixture is passed over a catalyst a number of times to produce a moderate yield of NO _x002e_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0032_ QUESTION _x0036_ _x0028_a_x0029_ As the reaction that occurs in the converter is exothermic. _x0028_b_x0029_ To maximise rates and product yields. _x0028_c_x0029_ Reaction rates are increased as in this particular reaction_x002c_ rates for this system increase with decreasing temperature. QUESTION _x0037_ QUESTION _x0038_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0033_ QUESTION _x0039_ _x0028_a_x0029_ C2H4O="44g/mol" CaCl2="111g/mol" H2O="18g/mol" _x0028_2 _x0034_4_x0029_ _x0031_00 _x0025_ _x0033_7.4_x0025_ _x0028_2 _x0034_4 _x0031_11 _x0032__x0028_18_x0029__x0029_ Atom Economy _x00d7_ _x00d7_="=" _x00d7__x002b_ _x002b_ _x0028_b_x0029_ An atom economy of _x0033_7.4_x0025_ is particularly poor_x002c_ and this is a very wasteful process. This would not be considered a green process_x002c_ as one the key principles of green chemistry is that it is better to develop reactions with fewer waste products than to have to clean up the waste _x0028_eg. achieve high atom economy_x0029_. _x0028_c_x0029_ All atoms in the reactants used in products_x002c_ therefore _x0031_00_x0025_ atom economy>production of nitric acid unit four – 2014 – chemistry © The School For Excellence 2014 Unit 4 Chemistry – The Production of Nitric Acid Page 1 THE PRODUCTION OF NITRIC ACID (HNO3) USES OF NITRIC ACID In terms of production, nitric acid is the third most widely produced acid across the world. It has a wide range of uses in agriculture, industry and medicine where it is used as a fertiliser and in the manufacture of fireworks, explosives, medicines, dyes, food preservatives, pesticides and detergents. PROPERTIES OF NITRIC ACID Nitric acid: • Is colourless in its pure form but may become orange or reddish in colour if contaminated by nitrogen oxides. • Is highly corrosive. • Is a poisonous liquid (freezing point -42˚C, boiling point 83˚C). • Reacts with water or steam to produce heat and toxic, corrosive and flammable vapours. • Can cause severe burns. • Miscible in water at all concentrations. • Has an acid dissociation constant (pKa) of −1.4. In aqueous solution, it almost completely (93% at 0.1 mol/L). • Will decompose at higher temperatures to form nitrogen oxides. Nitric acid is both a strong monoprotic acid and a strong oxidant, particularly when hot and concentrated. © The School For Excellence 2014 Unit 4 Chemistry – The Production of Nitric Acid Page 2 OXIDISING PROPERTIES The products of the reaction between nitric acid and metals depends upon the reactivity of the metal and the concentration of the acid. As a general rule, oxidising reactions occur primarily with the concentrated acid, favouring the formation of nitrogen dioxide (NO2). Reaction between a reactive metal and dilute acid (

<_x0031_M_x0029_: _x0038__x0723__x0029__x0748__x0be6__x0029_ _x002b_ _x0033_0_x072a__x0731__x0730__x0b37__x0028__x0bd4__x0be4__x0029_ _x2192_ _x0038__x0723__x0731__x0730__x0029__x0748__x0b37__x0029__x0b36__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0033__x0730__x072a__x0b38__x0730__x0731__x0b37__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0039__x072a__x0b36__x0731__x0028__x0bdf__x0029_ Nitrogen has been reduced from _x002b_5 all the way to _x002d_3. Reaction between a less reactive metal and more concentrated acid: _x2022_ Acid concentration _x0033_ to _x0036_M: _x0033__x0751__x0725__x0029__x0be6__x0029_ _x002b_ _x0038__x072a__x0731__x0730__x0b37__x0028__x0bd4__x0be4__x0029_ _x2192_ _x0033__x0751__x0725__x0731__x0730__x0029__x0b37__x0029__x0b36__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0034__x072a__x0b36__x0731__x0028__x0bdf__x0029_ _x002b_ _x0032__x0730__x0731__x0028__x0bda__x0029_ Nitrogen has been reduced from _x002b_5 to _x002b_2. _x2022_ Acid concentration _x0031_2M: _x0751__x0725__x0029__x0be6__x0029_ _x002b_ _x0034__x072a__x0731__x0730__x0b37__x0028__x0bd4__x0be4__x0029_ _x2192_ _x0751__x0725__x0731__x0730__x0029__x0b37__x0029__x0b36__x0028__x0bd4__x0be4__x0029_ _x002b_ _x0032__x072a__x0b36__x0731__x0028__x0bdf__x0029_ _x002b_ _x0032__x0730__x0731__x0b36__x0028__x0bda__x0029_ Nitrogen has been reduced from _x002b_5 to _x002b_4. Since nitric acid is an oxidising agent_x002c_ hydrogen _x0028_H2_x0029_ is rarely formed. Only magnesium _x0028_Mg_x0029__x002c_ manganese _x0028_Mn_x0029_ and calcium _x0028_Ca_x0029_ react with cold_x002c_ dilute nitric acid to give hydrogen: Mg_x0028_s_x0029_ _x002b_ _x0032_ HNO3_x0028_aq_x0029_ _x2192_ Mg_x0028_NO3_x0029_2_x0028_aq_x0029_ _x002b_ H2_x0028_g_x0029_ Reaction with non-metallic elements _x0028_with the exceptions of nitrogen_x002c_ oxygen_x002c_ noble gases_x002c_ silicon and halogens_x0029_ usually oxidises them to their highest oxidation states. The formation of nitrogen dioxide occurs for concentrated acid and nitric oxide for dilute acid. C_x0028_s_x0029_ _x002b_ _x0034_ HNO3_x0028_aq_x0029_ _x2192_ CO2_x0028_g_x0029_ _x002b_ _x0034_ NO2_x0028_g_x0029_ _x002b_ _x0032_ H2O_x0028_l_x0029_ _x0033_ C_x0028_s_x0029_ _x002b_ _x0034_ HNO3_x0028_aq_x0029_ _x2192_ _x0033_ CO2_x0028_aq_x0029_ _x002b_ _x0034_ NO_x0028_q_x0029_ _x002b_ _x0032_ H2O_x0028_l_x0029_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0033_ ACIDIC PROPERTIES Nitric acid is a strong acid. In moderately dilute solution _x0028__x007e_ _x0030_.1 M_x0029_ it is dissociated to an extent of about _x0039_3_x0025__x002c_ in accordance with the reaction_x002c_ Being an acid_x002c_ it reacts with alkalies to from nitrates It decomposes carbonates and bicarbonates as: _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0034_ THE PRODUCTION OF NITRIC ACID Nitric acid is made from ammonia in a three-step process known as the Ostwald process. Step _x0031_: Oxidation of NH3 to NO _x002e_ Step _x0032_: Oxidation of NO to NO2 _x002e_ Step _x0033_: Absorption and reaction of NO2 with water. STEP _x0031_: CATALYTIC OXIDATION OF AMMONIA Air is preheated and mixed with ammonia _x0028_which is not preheated as it would decompose_x0029_ and then passed through a converter where the following reaction occurs: _x0031_ _x0033__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0035_ _x0034_ _x0036_ _x0039_07 NH O NO H O H kJmol gg g g _x2212_ _x002b_ _x2192_ _x002b_ _x0394_="−" In this reaction_x002c_ ammonia undergoes catalytic oxidation to form nitrogen monoxide _x0028_nitric oxide _x0028_NO_x0029_ and water. This is the start of the oxidation process. The nitrogen in ammonia starts with an oxidation number of _x002d_3 _x0028_its lowest possible oxidation state_x0029_ and is converted to _x002b_2 in nitrogen monoxide. The ratio of air _x002f_ammonia must be carefully monitored and is maintain at between _x0039_ and _x0031_2_x0025_. If the concentration of ammonia rises much beyond this_x002c_ the mixture becomes explosive. The catalyst used in this process is _x0039_0_x0025_ platinum alloyed with _x0031_0_x0025_ rhodium for increased strength. The catalyst consists of several woven or knitted gauzes formed from the alloy. The gauze mats are preheated so that the gases are directly heated as they pass over the catalyst. The catalyst may become poisoned by air pollution and contamination from the ammonia which reduces its efficiency. The cost of these catalysts are extremely high and need to be frequently replaced due to the wear and tear they experience under such severe conditions. A cheaper alternative is yet to be developed. NO2 _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0035_ Nitrous oxide_x002c_ nitrogen and water are also simultaneously formed in this step_x002c_ as shown below. _x0031_ _x0033__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0033_ _x0032_ _x0036_ _x0031_267 NH O N H O H kJmol gg g g _x2212_ _x002b_ _x2192_ _x002b_ _x0394_="−" _x0033__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0032_2 _x0033_ NH O N O H O gg g g _x002b__x2192_ _x002b_ Conditions are carefully controlled in the converter in order to ensure that nitrogen monoxide _x0028_NO_x0029_ is the main product_x002c_ rather than nitrogen gas _x0028_N2_x0029_ or nitrogen _x0028_I_x0029_ oxide _x0028_ N O2 _x0029_. The yield of nitric oxide depends on the pressure and temperature as shown below. Pressure _x0028_atm_x0029_ Temperature _x0028__x02da_C_x0029_ NO yield _x0028__x0025__x0029_ Below _x0031_.7 _x0038_10-850 _x0039_7 _x0031_.7-6.5 _x0038_50-900 _x0039_6 Above _x0036_.5 _x0039_00-940 _x0039_5 Typical conditions for the production of NO are therefore: _x2022_ High temperatures _x0028_820 _x0039_30o _x2212_ C _x0029_ _x2022_ High pressures _x0028_11 atm_x0029_ Temperature Considerations Even though higher yields would be obtained at lower temperatures _x0028_the forward reaction is exothermic_x0029__x002c_ the process is carried out at high temperatures _x0028_820 _x0039_30o _x2212_ C _x0029_. This is because the rate at which the reaction proceeds at low temperatures is too slow to be commercially viable. To compensate for the resultant loss in product yield_x002c_ the gas mixture is passed over a catalyst a number of times to produce a moderate yield of NO _x002e_ Pressure Considerations At the high temperatures employed_x002c_ the NO formed decomposes to form nitrogen and oxygen. _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_NO N O g _x0083_ g g _x002b_ To avoid this_x002c_ the gas mixture is passed across the catalyst very rapidly _x0028_contact time is approximately _x0030_.003 sec_x0029_. To achieve this high flow rate_x002c_ the reaction is performed at high pressures even though lower pressures would result in a higher product yield. The consequential loss in yield of NO is compensated for by the increased reaction rates and the quality of product obtained. Note: Even with all the compromises that are required in this step_x002c_ the yield of NO is in the order of _x0039_5_x0025_. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0036_ STEP _x0032_: OXIDATION OF NITROGEN MONOXIDE The waste heat from the gases leaving the converter is recycled and used in other sections of the plant. The temperature of the nitrogen monoxide mixture is reduced to around _x0032_00-250_x02da_C in this process. The gases are then passed through a cooling chamber and their temperature reduced to approximately _x0035_0_x02da_C. Any condensed water is transferred to the absorption tower. As the gases are cooled_x002c_ the nitrogen monoxide oxidises to nitrogen dioxide _x0028_the nitrogen in NO is oxidised from _x002b_2 to _x002b_4 in the nitrogen dioxide_x0029_. The oxygen consumed in this step may be added from an external source or is provided by excess oxygen in the gaseous mixture exiting the converter. The reaction is: _x0031_ _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0032_ _x0031_14 NO O NO H kJmol gg g _x2212_ _x002b_ _x0394_="−" _x0083_ Temperature Considerations As this reaction is exothermic_x002c_ high yields of product can be achieved by using lower temperatures. This reaction is unusual in that its rate increases with decreasing temperature meaning that NO CONFLICT arises between the conditions required to optimise rates and yields. Pressure Considerations Yields can be further maximised by using high pressures. The system will respond to high pressures by favouring the reaction that will produce the fewer mole of gas _x2013_ which in this case is the formation of products. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0037_ STEP _x0033_: ABSORPTION OF NITROGEN DIOXIDE Water is mixed with the nitrogen dioxide gas in absorption towers to form dilute solutions of nitric acid according to the following overall reaction: _x0032__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0033_ _x0032_ NO H O HNO NO g _x002b__x2192_ _x002b_ l aq g This is a redox reaction in which produces nitrogen in its highest oxidation state _x0028__x002b_5 in nitric acid_x0029_. The towers contain large number of inert plates packed with inert granular materials designed to increase the contact between the gases and water. This reaction is exothermic and continuous cooling is needed. The conversion is favoured by low temperatures and significant reaction occurs until the gases leave the towers. Nitrogen dioxide gas is pumped at _x0035_ to _x0031_0 atm across the inert packing material_x002c_ through which water is trickled from above. Reaction between the water and the gas produces nitric acid_x002c_ which then dissolves in the remaining water. Small quantities of NO are also produced_x002c_ which reacts with oxygen from the air in the tower to produce NO2 which then reacts as before. A solution of nitric acid may be produced that is about _x0034_5_x2013_60_x0025_ HNO3 _x002e_ This can easily be increased to _x0036_8_x0025_ _x0028_equivalent to _x0031_6 M _x0029_ by distilling off some of the water. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0038_ WASTES AND MANAGEMENT _x2022_ The Ostwald process is very energy efficient and produces little waste. _x2022_ The oxidation of ammonia is highly exothermic_x002c_ generating sufficient heat energy to meet the energy needs of the rest of the plant. _x2022_ The main gaseous emissions from the Ostwald process include NO and NO2 _x002e_ Both gases contribute to photochemical smog_x002c_ and therefore_x002c_ careful attention must be paid to minimising how much of these gases are emitted into the atmosphere. One approach involves the heating of these gases using a fuel such as natural gas_x002c_ naphtha or hydrogen_x002c_ over a catalyst_x002c_ so that the NOx is reduced to N2 _x002e_ CH4_x0028_g_x0029_ _x002b_ _x0034_NO2_x0028_g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ _x0032_H2O_x0028_l_x0029_ _x002b_ _x0034_NO_x0028_g_x0029_ then_x002c_ CH4_x0028_g_x0029_ _x002b_ _x0034_NO g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ _x0032_H2O_x0028_l_x0029_ _x002b_ _x0034_N2_x0028_g_x0029_ Also: CH4_x0028_g_x0029_ _x002b_ _x0034_N2O g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ _x0032_H2O_x0028_l_x0029_ _x002b_ _x0032_N2_x0028_g_x0029_ H2_x0028_g_x0029_ _x002b_ NO2_x0028_g_x0029_ _x00e0_ _x0032_H2O_x0028_l_x0029_ _x002b_ NO_x0028_g_x0029_ then_x002c_ _x0032_H2_x0028_g_x0029_ _x002b_ _x0032_NO_x0028_g_x0029_ _x00e0_ _x0032_H2O_x0028_l_x0029_ _x002b_ N2_x0028_g_x0029_ Also: H2_x0028_g_x0029_ _x002b_ N2O g_x0029_ _x00e0_ CO2_x0028_g_x0029_ _x002b_ H2O_x0028_l_x0029_ _x002b_ _x0032_N2_x0028_g_x0029_ In addition_x002c_ the absorption tower may be modified by increasing its size or operating pressure so as to maximise conversion of NOx to nitric acid. _x2022_ The gas mixture entering the converter is filtered to remove catalytic poisons_x002c_ which increases the efficiency of the catalysts and hence decreasing the pressure _x0028_and energy_x0029_ required to force the gas through the catalyst bed. _x2022_ Heat exchangers are employed to remove heat released by the reaction in the converter and then using it to heat incoming gases or generate electricity. _x2022_ At the high temperatures and pressures used in the converter_x002c_ the catalyst slowly vaporises and is lost. Gases leaving the converter are passed through a filter to recover the metals and minimise the impact of these vapours on the environment. _x2022_ Specific catalysts are added to the converter to decompose any N O2 formed. Note: Nitrogen_x0028_I_x0029_ oxide is a significant greenhouse gas. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0039_ HEALTH AND SAFETY _x2022_ Concentrated nitric acid is corrosive and causes severe burns to the skin and eyes. Its fumes evolve nitrogen dioxide gas which at low concentrations may cause lung oedema _x0028_fluid in the lungs_x0029_ and fatal with excessive exposure. _x2022_ As a strong oxidant_x002c_ nitric acid reacts readily with a range of organic materials and metals to produce flammable and _x002f_or explosive products. _x2022_ NOx gases are significant greenhouse gases and some can react with water to form acid rain. Safety Measures Employed: _x2022_ There is careful monitoring in nitric acid plants for leaks and spills and all employees are trained to handle such if they do occur. _x2022_ Equipment must be carefully maintained to avoid corrosion. _x2022_ Acid spills are contained using materials such as earth_x002c_ clay or sand_x002c_ and then neutralised with a base such as slaked lime _x0028_Ca_x0028_ OH _x0029_2 _x0029_ or sodium carbonate. _x2022_ Full protective equipment and breathing apparatus is readily accessible across the plant. _x2022_ The ratio of ammonia to air in the gas entering the converter is continuously measured and controlled to ensure it does not reach explosive conditions. _x2022_ Un-reacted gases are recycled where possible. _x2022_ Various methods are employed to limit NOx emissions_x002c_ maximise conversion efficiency_x002c_ and minimise loss of energy. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_0 MIXED QUESTIONS QUESTION _x0031_ A number of different oxidation states of nitrogen are involved in the industrial production of nitric acid from ammonia. State the various nitrogen containing compounds involved in the Ostwald Process and the corresponding oxidation states of nitrogen. Solution QUESTION _x0032_ Describe the theoretical conditions that should be used to maximise the rate of the reaction of ammonia and oxygen to produce nitrogen monoxide. Are these the conditions actually used_x003f_ If not_x002c_ why not_x003f_ Solution _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_1 QUESTION _x0033_ Which of the following is not a property of nitric acid_x003f_ A It is monoprotic. B It is a strong acid. C It is a good oxidant. D It forms nitride salts. QUESTION _x0034_ Write equations for the following reactions of nitric acid: _x0028_a_x0029_ With water. _x0028_b_x0029_ With ammonia to make ammonium nitrate. _x0028_c_x0029_ With potassium hydroxide to make potassium nitrate. _x0028_d_x0029_ With zinc metal to form zinc ions and ammonia. _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_2 QUESTION _x0035_ During the Ostwald process_x002c_ nitrogen monoxide is made from ammonia at about _x0039_00_x00b0_C and then cooled to _x0033_0_x00b0_C before being reacted with air to make nitrogen_x0028_IV_x0029_ oxide. Both these reactions are exothermic. Why are the temperatures used for these reactions so different_x003f_ Solution QUESTION _x0036_ As the gas passes through the catalyst bed in the converter during nitric acid manufacture_x002c_ its temperature increases. The gas must be cooled before it is mixed with air. _x0028_a_x0029_ Why does the temperature of the gas rise_x003f_ _x0028_b_x0029_ Why is it necessary to cool the gas_x003f_ _x0028_c_x0029_ What side benefit is obtained from the need to cool gases_x003f_ Solution _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_3 QUESTION _x0037_ The flow chart below shows the processes leasing to the production of nitric acid on an industrial scale. _x0028_i_x0029_ What is Gas A_x003f_ What is Gas B_x003f_ _x0028_ii_x0029_ Write an equation for the process occurring in Reactor _x0031_. _x0028_iii_x0029_ What would be the effect of increasing the temperature in Reactor _x0031_ on the rate of production of gas B_x003f_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_4 _x0028_iv_x0029_ What would be the effect of increasing the temperature in Reactor _x0031_ on the equilibrium yield of gas B_x003f_ _x0028_v_x0029_ What is the function of the catalyst in Reactor _x0032__x003f_ _x0028_vi_x0029_ At low temperatures_x002c_ NO2 is in equilibrium with another oxide of nitrogen. Write an equation for this equilibrium. _x0028_vii_x0029_ What is reagent D_x002c_ which is added into Reactor _x0034_ with NO2 _x003f_ Write an equation for the reaction occurring in Reactor _x0034_. _x0028_viii_x0029_ Reagent E is recycled back into the cooling tower as shown in the diagram. What is reagent F_x003f_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_5 QUESTION _x0038_ Nitrogen oxide_x002c_ NO_x002c_ is a small but important component of the atmosphere and is produced commercially on a large scale during the manufacture of nitric acid. _x0028_i_x0029_ Name two processes_x002c_ one natural and one involving the activities of man_x002c_ that contribute significant significantly to the NO present in the atmosphere. _x0028_ii_x0029_ Write a balanced equation for the reaction by which NO is formed during the production of nitric acid by the Ostwald process. _x0028_iii_x0029_ NO produced during the Ostwald process is oxidised to NO2 _x002c_ according to the equation _x0031_ _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0032_ _x0031_81 NO O NO H kJmol gg g _x2212_ _x002b_ _x2192_ _x0394_="−" _x002e_ In a particular factory_x002c_ energy is released at a rate of _x0035_70 kJ per minute during this stage. What volume of NO2 at STP is being released each minute_x003f_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_6 QUESTION _x0039_ _x0028_a_x0029_ Calculate the atom economy of ethylene oxide_x002c_ created in the following reaction: _x0028_b_x0029_ Would this method of production of ethylene oxide be considered as a _x201c_Green_x201d_ process_x003f_ Give a reason for your answer. _x0028_c_x0029_ Recently_x002c_ a method of synthesising ethylene oxide from ethene and oxygen using a silver catalyst was developed. What_x2019_s the atom economy of this alternative reaction_x003f_ SOLUTIONS _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0031_ FOR ERRORS AND UPDATES_x002c_ PLEASE VISIT WWW.TSFX.COM.AU _x002f_MC-UPDATES QUESTION _x0031_ The Ostwald process involves the oxidation of nitrogen_x002c_ through a series of steps_x002c_ from its lowest oxidation state to its highest. Starting with ammonia _x0028_ NH3 _x002d_ oxidation number of N="−3)," nitrogen monoxide _x0028_ NO _x002d_ oxidation number of N="+2" _x0029_ is formed_x002c_ followed by nitrogen dioxide _x0028_ NO2 _x002d_ oxidation number of N="+4" _x0029_ and finally nitric acid _x0028_ HNO3 _x002d_ oxidation number of N="+5)." QUESTION _x0032_ Refer to Notes. QUESTION _x0033_ Answer is D QUESTION _x0034_ _x0028_a_x0029_ HNO H O H O NO _x0033__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0033_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ aq l aq aq _x002b_ _x2212_ _x002b__x2192_ _x002b_ _x0028_b_x0029_ HNO NH NH NO _x0033__x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0034_ _x0033__x0028_ _x0029_ aq g aq _x002b_ _x2192_ _x0028_c_x0029_ HNO KOH H O KNO _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ aq aq l aq _x002b_ _x2192__x002b_ _x0028_d_x0029_ _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0038_4 _x0033_ Z s aq aq aq g l n HNO H Zn NH H O _x002b_ _x002b_ _x002b_ _x002b__x2192_ _x002b_ _x002b_ or _x0032_ _x0028_ _x0029_ _x0033__x0028_ _x0029_ _x0028_ _x0029_ _x0028_ _x0029_ _x0034__x0028_ _x0029_ _x0032_ _x0028_ _x0029_ _x0034_ _x0039_4 _x0033_ Z s aq aq aq g l n HNO H Zn NH H O _x002b_ _x002b__x002b_ _x002b_ _x002b__x2192_ _x002b_ _x002b_ QUESTION _x0035_ Stage _x0031_ of the Ostwald Process: The nitrogen monoxide produced in the converter is cooled to about _x0033_0o C to maximise the production of NO2 in the reaction below. _x0031_ _x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032__x0028_ _x0029_ _x0032_ _x0032_ _x0031_14 NO O NO H kJmol gg g _x2212_ _x002b_ _x0394_="−" _x0083_ As this reaction is exothermic_x002c_ high yields of product can be achieved by using lower temperatures. And as reaction rates for this system increase with decreasing temperature_x002c_ no conflicts are created between rates and yields. In Stage _x0032_ of the Ostwald Process_x002c_ the reaction once again is exothermic_x002c_ meaning that higher product yields will be obtained by using lower temperatures. In this case however_x002c_ the process is carried out at high temperatures _x0028_820 _x0039_30o _x2212_ C _x0029_ as the rate at which the reaction proceeds at low temperatures is too slow to be commercially viable. To compensate for the resultant loss in product yield_x002c_ the gas mixture is passed over a catalyst a number of times to produce a moderate yield of NO _x002e_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0032_ QUESTION _x0036_ _x0028_a_x0029_ As the reaction that occurs in the converter is exothermic. _x0028_b_x0029_ To maximise rates and product yields. _x0028_c_x0029_ Reaction rates are increased as in this particular reaction_x002c_ rates for this system increase with decreasing temperature. QUESTION _x0037_ QUESTION _x0038_ _x00a9_ The School For Excellence _x0032_014 Unit _x0034_ Chemistry _x2013_ The Production of Nitric Acid Page _x0033_ QUESTION _x0039_ _x0028_a_x0029_ C2H4O="44g/mol" CaCl2="111g/mol" H2O="18g/mol" _x0028_2 _x0034_4_x0029_ _x0031_00 _x0025_ _x0033_7.4_x0025_ _x0028_2 _x0034_4 _x0031_11 _x0032__x0028_18_x0029__x0029_ Atom Economy _x00d7_ _x00d7_="=" _x00d7__x002b_ _x002b_ _x0028_b_x0029_ An atom economy of _x0033_7.4_x0025_ is particularly poor_x002c_ and this is a very wasteful process. This would not be considered a green process_x002c_ as one the key principles of green chemistry is that it is better to develop reactions with fewer waste products than to have to clean up the waste _x0028_eg. achieve high atom economy_x0029_. _x0028_c_x0029_ All atoms in the reactants used in products_x002c_ therefore _x0031_00_x0025_ atom economy>