Worksheet on Ammonia Name: ( ) Date - ASKnLearn

<strong>Worksheet</strong> on AmmoniaName: _________________________ ( ) Date: ______Class : Sec. 4/ ___1. Ammonia is manufactured industrially by the reaction between nitrogengas and hydrogen gas. This reaction is a reversible reaction. Theammonia gas formed is removed from the mixture of gases as liquidammonia and the unreacted gases are recycled.aState the sources of nitrogen and hydrogen in this processNitrogen: from fractional distillation of liquid airHydrogen: from cracking of oilbi)Write a balanced equation, including state symbols, for the formation ofammonia.N 2 (g) + 3H 2 (g)2NH 3 (g)ii)State three essential conditions required for the production of ammoniain the Haber Process.Catalyst : Finely divided iron , Temperature: 450 0 CPressure: 200 atmospheresci)Ammonia is removed from the mixture of gases products byliquefaction. Suggest an alternative method that you could use in thelaboratory to remove ammonia from the mixture of gases.Bubble the mixture of gases through water and the ammonia willdissolve in water. The gas collected would be a mixture of nitrogenand hydrogen.ii)Why can’t your method in i) be used industrially?The above method can’t be used industrially as it is difficult/ notcost effective to retrieve ammonia from ammonia solution/ammonium sulphate solution.- 1 -

2 The table below shows the percentage yield of ammonia at varioustemperatures and pressures.Temperature(°C)Pressure(atm)350 100 38350 200 53350 300 62400 100 25400 200 38400 300 48450 100 17450 200 27450 300 36500 100 12500 200 20500 300 26Percentage Yield(%)ai)State how pressure and temperature affect the yield in ammonia.Pressure: The higher the pressure, the higher the yieldTemperature: The higher the temperature, the lower the yieldii)A chemical engineer designs a reaction chamber that can support atemperature of 450°C and a pressure of 250 atm. Estimate thepercentage yield of ammonia under such conditions.27% < ammonia yield < 36%b) To further speed up the reaction, a catalyst is used. Name the catalystand suggest, with explanation, what may be done to the catalyst toenhance its effectiveness.Finely divided iron catalystIt increases the surface area which increases the rate of reactionc) The yield of ammonia in the Haber Process is low, compared with otherindustrial reactions. Explain why this is so.The yield of ammonia in the Haber Process is low due to thereaction being reversible – some of the products re-form thereactants at the same time, and hence it is not possible to allowthe all the reactants to turn into products.- 2 -

d) Calculate the mass of ammonia obtained when 56 tonnes of nitrogen isused, assuming that the percentage yield is only 15%.N 2 (g) + 3 H 2 (g)2 NH 3 (g)No. of moles of nitrogen = 56 x 10 6 / 14x2= 2 x 10 6No. of moles of ammonia = 2 ( 2 x 10 6 )Mass of ammonia = 15/100 x ( 4 x 10 6 ) x (14 + 3 )= 10.2 x 10 6 g= 10.2 tonnes ( 3 s.f.)3) Ammonia is manufactured in the Haber Process. The following graphshows the amount of ammonia present in the equilibrium mixture underconditions of temperature and pressure.a) Use the graph to deduce the effect of increasing the pressure on thepercentage of ammonia in the equilibrium mixture.Increasing the pressure increase the percentage of ammonia in theequilibrium mixture.b) An industrial process uses conditions of 450 0 C and 200 atm.i) Use the graph to find the percentage of ammonia in the equilibriummixture.27% or 28%ii)Suggest one advantage and one disadvantage of using 450 0 C ratherthan 350 0 C as the working temperature.Advantage: Faster rate of reactionDisadvantage: Less percentage of ammonia in equilibriummixture.- 3 -

iii)A student has three test-tubes of gas. One tube contains ammonia, onecontains hydrogen and one contains nitrogen. Describe tests thestudent could do to identify the three gases.Moist red litmus papers are placed near the mouth of the 3 testtubes.The gas that turns the moist red litmus blue is ammonia.For the remaining two test-tubes of gases, place , a lighted splint atthe mouth of the test-tubes. The gas which extinguishes thelighted splint with a ‘pop’ sound is Hydrogen. The remaining gasmust be nitrogen gas as it does not give positive results to these 2tests.4. Ammonia is used to manufacture nitric acid, by a two-stage process.Stage 1: the ammonia is converted to nitrogen (II) oxide.4NH 3 (g) + 5O 2 (g) → 4NO (g) + 6 H 2 OH = - 950kJ/mola) State and explain how the rate changes when the pressure isincreased. Use ideas about colliding particles.As the pressure increases, the molecules are forced closertogether, increasing the number of collision and successfulcollisions. Hence, increasing the rate of reaction.b) During the reaction, the ammonia and oxygen are passed through apowdered catalyst.i) Explain why the catalyst becomes hot during the reaction.It is an exothermic reaction.ii)Explain why the catalyst is used in the form of powder.Catalyst in the form of powders have greater surface area. Henceincreasing the rate of reactionc) It is possible to find out whether this reaction has finished by followingpH changes during the reaction. Samples of gas are taken from thereaction vessel at intervals and bubbled through water to form asolution. The pH of each solution is measured. Explain why themeasured pH changes during the reaction.The pH decreases because ammonia which is alkaline is beingused up.- 4 -

Stage 2: the nitrogen dioxide is converted to nitric acid.4NO(g) + 2H 2 O (g) + 3O 2 (g) → 4HNO 3 (aq)d) Calculate the maximum mass of nitric acid which can be made from720 dm 3 of nitrogen (II) oxide, NO, at room temperature and pressure.No. of moles of NO = 72024= 30No. of moles of HNO 3 = 30Mass of HNO 3 = 30 x (1 + 14 + 3 x 16)= 1890 g ( 3 s.f.)e) Use the two equations to construct an overall equation for theconversion of ammonia to nitric acid.simplify add the right hand side of the equations together and lefthand side of the equations together and simplify.4NH 3 + 5O 2 + 4NO + 2H 2 O + 3O 2 → 4HNO 3 + 4NO + 6H 2 O4NH 3 + 8O 2 → 4HNO 3 + 4H 2 ONH 3 + 2O 2 → HNO 3 + H 2 O (divide throughout by 4)5 a) ammoniab) Solution X is alkalinec) Calcium chloride2Cl - + Ca 2+ → CaCl 2d) 2NH 4 Cl + Ca(OH) 2 → CaCl 2 + 2NH 3 + 2H 2 O6 a) Moist red litmus paper turned blue and then red again.Explain your answer.Ammonium chloride decomposes upon heating to form ammonia andhydrogen chloride gas. Ammonia gas having a lower relative molecularmass (17) diffuses at a faster rate than hydrogen chloride gas (36.5)turning the moist red litmus blue. Hydrogen chloride gas diffuses out ofthe test tube slower and hence turning the moist blue litmus red again.b) State one other observation she would make. Explain thisobservationWhite sublimate observed. Ammonia gas and hydrogen gas will recombinefurther up the test-tube where is cooler to form ammoniumchloride which is seen as a white sublimate- 5 -