(Credits to Mustafa Asif) Powerpoint NotesDownload presentation hereSummaryAcidsElectrical conductivityAny solution's ability to conduct electricity is defined by is charges ions in it. As a result, a strong acid will produce more charged ions than a weak one, and so it's solution will be a better electrical conductor than a weak acid. The same goes for strong/weak bases. Acids in daily life
Common laboratory acids
Concentrated acids: solution containing large amount of acid dissolved in water Properties of acids
Storage of acids
Uses of acids
Acids and hydrogen ions
Fizzy drinks
Concentration vs Strength
Bases and Alkalis
Laboratory Alkalis
Properties of Alkalis
Strong and weak alkalis
Uses of Alkalis
pH and IndicatorsIndicators are substances that has different colours in acidic and alkaline solutionsCommon indicators:
pH ScaleA measure of acidity or alkalinity of a solution is known as pH
Measuring pH of a Solution
Ionic EquationsIonic equation is equation involving ions in aqueous solution, showing formation and changes of ions during the reactionRule to make ionic equations:
Reaction between Metals and AcidsEg. reaction of sodium with hydrochloric acid2Na (s) + 2HCl (aq) → 2NaCl (aq) + H2 (g) Its ionic equation is written as: 2Na (s) + 2H+ (aq) + 2Cl- (aq) → 2Na+ (aq) + 2Cl- (aq) + H2 (g) Since 2 Cl- (aq) ions don’t change, they’re not involved in reaction. As ionic equation is used to show changes in reactions, we omit Cl- (aq) ions. So we’re left with: 2Na (s) + 2H+ (aq) → 2Na+ (aq) + H2 (g) Reaction between soluble ionic compounds and acidse.g. Reaction of sodium hydrogencarbonate with hydrochloric acidNaHCO3 (aq) + HCl (aq) → NaCl (aq) + CO2 (g) + H2O (l) Its ionic equation is: Na+ (aq) + H+ (aq) + CO32- (aq) + H+ (aq) + Cl- (aq) → Na+ (aq) + Cl- (aq) + CO2 (g) + H2O (l) Since Na+ (aq) and Cl- (aq) ions don’t change, we omit them, leaving: H+ (aq) + CO32- (aq) + H+ (aq) → CO2 (g) + H2O (l) CO32- (aq) + 2H+ (aq) → CO 2 (g) + H2O (l)Reaction between insoluble ionic compounds and acidse.g. Reaction between iron(II) oxide and sulphuric acidFeO (s) + H2SO4 (aq) → FeSO 4 (aq) + H2O (g)Its ionic equation is: FeO(s) + 2H+ (aq) + SO42- (aq) → Fe2+ (aq) + SO42- (aq) + H2O (g) Note: FeO is written in full as it is solid (although it is an ionic compound) Since SO42- (aq) ions don’t change, we omit SO42- ions, leaving: FeO (s) + 2H+ (aq) → Fe2+ (aq) + H2O (g) E.g. Reaction between calcium carbonate and hydrochloric acid CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l) Its ionic equation is: CaCO3 (s) + 2H+ (aq) + 2Cl- (aq) → Ca2+ (aq) + 2Cl- (aq) + CO2 (g) + H2O (l) Since 2 Cl- (aq) ions don’t change, we omit Cl- ions, leaving: CaCO3 (s) + 2H+ (aq) → Ca2+ (aq) + CO2 (g) + H2O (l) Reaction producing precipitateE.g. Reaction between calcium hydroxide and barium sulphateCa(OH)2 (aq) + BaSO4 (aq) → Ba(OH)2 (s) + CaSO4 (aq) Its ionic equation is written as: Ca2+ (aq) + 2OH- (aq) + Ba2+ (aq) + SO42- (aq) → Ba(OH) 2 (s) + Ca2+ (aq) + SO42- (aq)Since Ca2+ (aq) and SO42- (aq) ions don’t change, we omit them, leaving: Ba2+ (aq) + 2OH- (aq) → Ba(OH)2 (s) Displacement reactionsE.g. Reactions between magnesium with zinc sulphateMg (s) + ZnSO4 (aq) → MgSO4 (aq) + Zn (s) Its ionic equation is written as: Mg (s) + Zn2+ (aq) + SO42- (aq) → Mg2+ (aq) + SO42- (aq) + Zn (s) Since SO42- (aq) ions don’t change, we omit them, leaving: Mg (s) + Zn2+ (aq) → Mg2+ (aq) + Zn (s) Neutralization
4 + H2OH2SO4 (aq) + NaOH (aq) --> Na2SO 4 (aq) + H2O (g)Ionic equation is: H+ (aq) + OH- (aq)→ H2O (g) Plants don’t grow well in acidic soil. Quicklime (calcium hydroxide) is added to neutralise the acidity of soil according to equation: Acid (aq) + Ca(OH)2 (aq) --> Ca(acid anion) (aq) + H2O (g) Reaction between Base and Ammonium SaltsE.g. Reaction between NaOH and NH4OHNaOH (aq) + NH4Cl (aq) --> NaCl (aq) + NH3 (g) + H2O (g) Ionic equation: NH4+ (aq) + OH-(aq) → NH3 (g) + H2O (g) Oxides
Preparation of Salts
Preparation of insoluble salts - ionic precipitation
Preparation of soluble salts1. By Metal Hydroxide and Acid
KOH (aq) + HCl (aq) --> KCl (aq) + H2O (l)
Zn (s) + H2SO4 (aq) --> ZnSO4 (aq) + H2O(l)
CuO (s) + H2SO4 (aq) --> CuSO4 (aq) + H2O (l)
K2CO3 (s) + H2SO4 (aq) --> K2SO4 (aq) + CO2 (g) + H2O (l)
Properties and uses of Ammonia
Conditions for Manufacturing Ammonia to have high yield of ammonia we should have:
Plants need nitrogen as one of component for growth and ammonium fertilizers contain nitrogen for that. % content of nitrogen in ammonium fertilizers E.g. Ammonium sulphate, (NH4)2SO4, and urea, (NH2)2CO, are 2 kinds of fertilizers. Deduce, in terms of nitrogen content, which of these fertilizers best for plants. % mass = (total mass of element / total mass of compound) x 100 (NH4)2SO4 = (28 / 132) x 100 = 21.2% of N (NH2)2CO = (28 / 60) x 100 = 46.7% of N Therefore, (NH2)2CO is a better fertilizer since it contains more nitrogen. Problems with Ammonia
MCQ Questions1. Which of the following gases cannot be removed from the exhaust gases of a petrol powered car by its catalytic converter?a. carbon dioxide b. carbon monoxide c. hydrocarbons d. nitrogen dioxide 2. An excess of dilute sulphuric acid reacts with both aqueous barium hydroxide and aqueous barium chloride. In what way are the two reactions the same? a. a gas is produced b. an insoluble salt is produced c. the final pH is 7 d. water is produced 3. In separate experiments, an excess of aqueous sodium hydroxide or aqueous ammonia was gradually added to a solution X. In both experiments, a precipitate was obtained which dissolved in an excess of the added reagent. What could X contain? a. copper(II) nitrate b. iron(II) nitrate c. iron(III) nitrate d. zinc nitrate 4. Which of the following is a property of ethanoic acid but is not a property of sulphuric acid? a. it reacts with copper(II) oxide b. it reacts with sodium carbonate c. it reacts with magnesium d. it burns in air 5. Which salt could be prepared by a method involving crystallization as the final stage? a. barium sulphate b. calcium carbonate c. silver chloride d. sodium nitrate 6. An element X forms a hydroxide which dissolves both in acids and in alkalis. What could X be? a. aluminium b. calcium c. copper d. iron 7. Under suitable conditions, hydrochloric acid reacts with each of the following substances. Which reaction gives a colorless solution only? a. calcium carbonate b. iron(II) hydroxide c. potassium hydroxide d. silver nitrate 8. After acidification with dilute nitric acid, a colorless solution of X reacts with aqueous silver nitrate to give a white precipitate. What could X be? a. calcium iodide b. copper(II) chloride c. lead(II) chloride d. sodium chloride 9. Two tests were carried out on a colorless liquid X. X turned anhydrous copper(II) sulphate from white to blue. X reacted with calcium, giving hydrogen. What could X be? 1. dilute hydrochloric acid 2. ethanol 3. water a. 1 only b. 1 and 2 only c. 1 and 3 only d. 1, 2 and 3 10. Which of the following is a characteristic property of alkalis in aqueous solution? a. they liberate ammonia from ammonium salts b. they liberate carbon dioxide from carbonates c. they give hydrogen with any metal d. they turn universal indicator red 11. A mineral X dissolves in dilute hydrochloric acid, giving off a gas which turns limewater milky. When aqueous ammonia is added to the colorless solution, a white precipitate is formed. The precipitate dissolves in an excess of aqueous ammonia to give a colorless solution. What is X? a. calcium carbonate b. copper(II) carbonate c. zinc carbonate d. zinc sulphide 12. Aqueous sodium hydroxide reacts with a metal ion producing a colored precipitate. This precipitate changes color on standing. What is the ion present? a. Al3+ b. Cu2+ c. Fe2+ d. Zn2+ 13. A bee sting is acidic. Which household substance will neutralize a bee sting? a. damp bicarbonate of soda pH 8 b damp common salt pH 7 c. lemon juice pH 5 D. vinegar pH 4 14. An excess of sodium hydroxide is added to an aqueous solution of salt X and boiled. Ammonia gas is only given off after aluminium foil is added to the hot solution. What could be X? a. ammonium chloride b. ammonium nitrate c. sodium chloride d. sodium nitrate 15. Which ion reacts with aqueous ammonia to give a precipitate that dissolves in an excess of ammonia? a. Al3+ b. Fe2+ c. Fe3+ d. Zn2+ 16. A solid element conducts electricity. The element burns in air to form a white solid. This white solid dissolves in water to give an alkaline solution. What is the element? a. aluminium b. calcium c. carbon d. copper 17. Which calcium compound does not increase the pH of acidic soils? a. calcium carbonate b.calcium hydroxide c. calcium oxide d. calcium sulphate 18. What is the concentration of hydrogen ions in 0.05 mol/dm3 sulphuric acid? a. 0.025 g/dm3 b. 0.05 g/dm3 c. 0.10 g/dm3 d. 2.0 g/dm3 19. A solution X forms a white precipitate with dilute sulphuric acid and also with aqueous silver nitrate. What could solution X contain? a. barium chloride b. barium nitrate c. magnesium chloride d. magnesium sulphate 20. Which of the following is a reaction of dilute hydrochloric acid? a. ammonium chloride reacts to give ammonia b. calcium carbonate reacts to give carbon dioxide c. copper reacts to give hydrogen d. universal indicator paper turns blue 21. Which compound in solution produces a precipitate with aqueous ammonia that does not dissolve when an excess of ammonia is added? a. copper(II) sulphate b. iron(II) chloride c. potassium hydroxide d. zinc chloride 22. A white compound produces a mixture of gases when heated. This mixture turns moist Universal Indicator paper red and relights a glowing splint. What does this mixture contain? a. an acidic gas and hydrogen b. an acidic gas and oxygen c. an alkaline gas and hydrogen d. an alkaline gas and oxygen 23. Which of the following describes a step in the preparation of insoluble barium sulphate from aqueous barium chloride and dilute sulphuric acid? a. add dilute sulphuric acid until no more gas is produced b. add the indicator methyl orange c. collect the precipitate of barium sulphate by filtration d. evaporate the filtrate until it crystallises 24. Solid R is gradually added to aqueous solution S. The changes in pH are shown in the graph What are R and S?
25. Two solutions are mixed in a beaker and the mass of the beaker and the contents is then recorded at various times. The graph shows the results. What could be the two solutions? a. aqueous copper(II) sulphate and aqueous ammonia b. aqueous sodium carbonate and dilute nitric acid c. aqueous sodium hydroxide and aqueous zinc sulphate d. dilute hydrochloric acid and aqueous sodium sulphate 26. Element L burns in air giving a product that dissolves in water producing an alkaline solution. What is element L? a. carbon b. iron c. sodium d. sulfur 27. In an accident at a factory, some nitric acid was spilt. Which substance, when added in excess, neutralises the acid without leaving an alkaline solution? a. aqueous ammonia b. aqueous sodium hydroxide c. calcium carbonate d. water 28. Which statement does not describe a property of a weak acid in solution? a. it forms a salt with sodium hydroxide b. it has a pH of between 8 and 9 c. it is only partly dissociated into ions d. it reacts with sodium carbonate to give off carbon dioxide 29. An aqueous solution of a sulphate is made from a solid hydroxide, of a metal M, by the reaction: M(OH)2 (s) + H2SO4 (aq) ----> MSO4 (aq) + 2H2O (l) For which hydroxide would the method not work? a. barium hydroxide b. copper(II) hydroxide c. iron(II) hydroxide d. magnesium hydroxide 30. In an experiment, 4.0 cm3 of 1.0 mol/dm3 aqueous copper(II) sulphate was mixed with 8cm3 of 1.0 mil/dm3 aqueous sodium carbonate. CuSO4 + Na2CO3 ---> Na2SO4 + CuCO3 What did the reaction vessel contain when the reaction was complete? a. a colourless solution only b. a green precipitate and a blue solution c. a green precipitate and a colourless solution d. a white precipitate and a blue solution 31. Which of the following compounds dissolves in water to give a solution with a pH greater than 7? a. calcium carbonate b. copper(II) hydroxide c. sodium hydroxide d. sulphur dioxide 32. Waste water from a factory was found to have a pH value of 2. Which substance could be used to neutralise the waste water before it is released into a river? a. ammonium sulphate b. lime c. oxygen d. sulphur dioxide 33. Which of the following gases will not turn moist blue litmus paper red? a. carbon dioxide b. chlorine c. hydrogen chloride d. nitrogen monoxide 34. Which of the following correctly describes the solution formed and the gas evolved when potassium reacts with water? Solution Gas a. alkaline neutral b. acidic neutral c. alkaline acidic d. neutral neutral 35. Which of the following compounds can be classified as a normal salt? I. K2SO4 II. Zn(OH)Cl III. NaHCO3 IV. CH3COONa a. I and II only b. II and IV only c. I, II, and III d. I and IV only 36. Which salt could be prepared by a method involving crystallisation as the final stage? a. barium sulphate b. calcium carbonate c. silver chloride d. sodium nitrate 37. Nitrates from fertilisers used on farmland can cause pollution. Why do nitrates pollute rivers? a. nitrates are salts b. nitrates are very soluble in water c. nitrates contain oxygen d. nitrate ions are negatively charged 38. Farmers use potassium chloride on agricultural land. Why is it used? a. it removes excess acidity in the soil b. it kills harmful bacteria in the soil c. it provides potassium which is essential for healthy plant growth d. it reacts with salts in the soil releasing ammonia MCQ Answers1. a2. b (a white precipitate of barium sulphate produced in both cases) 3. d 4. d (ethanoic acid is an organic compound that contain carbon atoms in its molecule that can burn in air to form carbon dioxide) 5. d (sodium nitrate is the only soluble salt. The rest are insoluble and are obtained by filtration) 6. a (aluminum oxide is an amphoteric oxide that reacts with both acids and alkalis) 7. c 8. d (since X is a colorless solution, it does not contain transition metal ions. The white ppt is likely to be AgCl) 9. c 10. a 11. c 12. c 13. a 14. d (for ammonium nitrate, ammonia gas would also be evolved when it is boiled with sodium hydroxide. Boiling the sample in sodium hydroxide and aluminium foil is a chemical test for identifying nitrate ions) 15. d 16. c 17. d 18. c 19. a 20. b 21. b 22. b 23. c (when 2 solutions are mixed, BaSO4 precipitate is formed. It may be obtained by filtration) 24. a 25. b (the graph shows a loss in mass. hence, the reaction is likely to be one that gives out a gas that escapes from the reaction vessel) 26. c 27. c 28. b 29. a (barium hydroxide is soluble in water and reacts with dilute sulphuric acid to form insoluble barium sulphate) 30. c 31. c 32. b 33. d 34. a 35. d 36. d (sodium nitrate is the only soluble salt that can be obtained by crystallisation) 37. b 38. c Structured Questions Worked Solutions1a. Hydrogen chloride is a neutral gas and dissolves in water to form an acidic solutioni. explain why dry hydrogen chloride gas is neutral ii. explain why aqueous hydrogen chloride is acidic iii. describe how sodium carbonate can be used to confirm that an aqueous solution contains an acid 1b. The oxides of elements may be acidic, basic, or amphoteric. Give the name and formula of one example of each of these three types of oxide. Solution 1ai. Hydrogen chloride is covalently bonded, with sharing of electrons. Hence the molecules are not charged since no ionisation occurs. 1aii. When hydrogen chloride dissolves in water the molecules then ionises to form H+ and Cl-. Water also ionises to form H+ and OH-. The number of hydrogen ions is greater than hydroxide ions so the solution becomes acidic. 1aiii. It reacts with sodium carbonate to liberate carbon dioxide. 1b. sulphur dioxide, SO2 - ACIDIC potassium hydroxide, KOH - BASIC zinc oxide, ZnO - AMPHOTERIC 2. The reaction between zinc granules and dilute sulphuric acid at 25oC can be made to go faster by adding a small amount of copper powder. a. in an experiment, 0.65 g of zinc granules and 100 cm3 of 0.2 mol/dm3 sulphuric acid are allowed to react. i. calculate the number of moles of zinc in 0.65 g ii. calculate the number of moles of sulphuric acid in 100 cm3 of 0.2 mol/dm3 solution iii. give the equation, including state symbols, for the reaction iv. explain why the reaction stops. b. give one other method of making the reaction between zinc granules and dilute sulphuric acid go faster. Explain in terms of collisions between reacting particles how the method you have described speeds up the reaction. Solution 2ai. no. of moles of Zn = mass/Mr = 0.65/65 = 0.01 2aii. no. of moles of sulphuric acid = molarity x volume = 0.2 x 0.1 = 0.02 2aiii. Zn (s) + H 2 SO4 (aq) --> ZnSO4 (aq) + H2 (g)2aiv. All the zinc have reacted with the H 2 SO4. The H2 SO4 acid is in excess.2b. Use powdered zinc instead of granules. With powdered zinc, more zinc particles are able to move and collide with the acid particles. This increases the number of collision and thus increases the rate of reaction. 3. This question is about oxides. Use only the following oxides as answers. carbon dioxide copper(II) oxide sodium oxide carbon monoxide silicon dioxide sulphur dioxide a. which oxide has a macromolecular structure? b. which oxide is used to bleach wood pulp in the manufacture of paper? c. which oxides are basic? d. which oxides are common atmospheric pollutants? e. which oxide is the main constituent of sand? f. which oxide gives a blue solution when heated with dilute sulphuric acid? Solution 3a. silicon dioxide 3b. sulphur dioxide 3c. copper(II) oxide and sodium oxide 3d. carbon monoxide and sulphur dioxide 3e. silicon dioxide 3f. copper(II) oxide 4. Describe what is observed in each of the following reactions. a. aqueous sodium hydroxide is added to aqueous iron(III) sulphate b. dilute hydrochloric acid is added to solid sodium carbonate c. aqueous barium chloride is added to dilute sulphuric aced d. aqueous silver nitrate is added to aqueous sodium chloride Solution 4a. orange-brown precipitate is seen 4b. solid dissolved and effervescence seen (a colorless and odourless gas is evolved) 4c. white precipitate seen 4d. white precipitate seen 5a. Potassium nitrate is a salt which can be prepared by reacting an acid with an alkali, using the titration method. i. name an acid and an alkali which react to make potassium nitrate ii. explain why the titration method is suitable for the preparation of potassium nitrate 5b. Lead(II) iodide is a salt which can be prepared by the precipitation method. i. name suitable reagents for the preparation of lead(II) iodide ii. explain why the precipitation method is suitable for the preparation of lead(II) iodide Solution 5ai. acid: nitric acid alkali: potassium hydroxide 5aii. Since the acid, alkali and the salt are soluble in water, KNO3 cannot be prepared by other methods (eg. precipitation). The exact quantities of each acid and alkali are determined by titration where the end-point is determined by the use of an indicator. 5bi. lead nitrate and potassium iodide 5bii. Because lead iodide is insoluble in water. Once formed, it precipitates out readily while the salt KNO3 remains soluble in water. 6. Write the name of one example of each of the following. a. a green solid which decomposes on heating to form carbon dioxide b. a gas which turns moist red litmus paper blue c. an acid that forms a white precipitate when mixed with aqueous barium nitrate d. a metal which is extracted by electrolysis Solution 6a. copper(II) carbonate 6b. ammonia 6c. sulphuric acid 6d. aluminium 7a. For each of the following reactions, i. state the observations you would expect to make ii. name the product(s) of the reaction(s) iii. explain the changes which take place 1 Aqueous sodium hydroxide is added to aqueous iron(II) sulphate and the mixture is allowed to stand 2. Chlorine is bubbled into aqueous potassium iodide. The solid product is collected and then heated. 7b. Hydrogen can be manufactured using the reversible reaction between methane and steam. The formation of hydrogen is endothermic. i. write the equation for this reaction ii. explain why this reaction is best carried out at a high temperature but at a low pressure. Solution 7ai. 1. Dirty green precipitate of iron(II) hydroxide is formed which turns brown (iron(III) hydroxide) on standing. The brown solid is formed as a result of air oxidation of iron(II) to iron(III). Fe2+ (aq) + 2OH- (aq) --> Fe(OH)2 (s) 4Fe(OH)2 (s) + O2 (g) + 2H2O (l) --> 4Fe(OH)3 (s) 2. The solution turned brown due to formation of iodine. Iodide is oxidised by chlorine to give iodine. Cl2 (g) + 2I- (aq) --> 2Cl- (aq) + I2 (aq) With more iodine formed, it finally precipitates out as a black solid. Heating this black iodine crystal causes it to sublime to form violet iodine vapour. Black iodine crystals will be seen to form at the cooler surface. I2 (s) <---> I2 (g) 7bi. CH4 (g) + H2O (l) <---> 3H2 (g) + CO (g) 7bii. A high temperature speeds up the rate of reaction. It also helps to push the equilibrium to the right since the forward reaction is endothermic. Since there are greater amount of gaseous products, lowering the pressure would also help shift the reaction to the right. Hence, the yield will be higher. 8a. Name two aqueous solutions which will react to form a precipitate of silver chloride, AgCl 8b. Write an ionic equation, including state symbols, for the reaction in a. 8c. Describe how you would obtain a pure, dry sample of silver chloride precipitate from the mixture in a. Solution 8a. sodium chloride and silver nitrate 8b. Ag+ (aq) + Cl- (aq) --> AgCl (s) 8c. Mix the two solutions. Filter the resulting mixture. AgCl is obtained as the residue. Wash the residue with water and then dry the solid in an oven. 9. A student adds aqueous sodium hydroxide from a burette into 25.0cm3 of dilute sulphuric acid. The student measures the pH value of the mixture during the addition of the sodium hydroxide. a. describe how the pH value changes b. give an ionic equation to represent the neutralisation reaction between sodium hydroxide and sulphuric acid. c. sulphuric acid is a strong acid. i. what is meant by the term acid? ii. what is the difference between a strong acid and a weak acid? d. dilute sulphuric acid reacts with magnesium to give hydrogen. Give the ionic equation for this reaction. Solution 9a. pH increases from 1 to 14 9b. H+ (aq) + OH- (aq) --> H2O (l) 9ci. an acid is a compound that produces hydrogen ions, H+ when it dissolves in water, 9cii. a strong acid dissociates fully in water whereas a weak acid dissociates partially in water to form hydrogen ions H+. 9d. Mg (s) + 2H+ (aq) --> Mg2+ (aq) + H2 (g) 10a. For each salt, suggest the name of the missing reagent and briefly describe how to obtain the solid product from the reaction mixture. i. salt to be made: lithium chloride reagent 1: dilute hydrochloric acid reagent 2: ________________ I could obtain solid lithium chloride by: ___________________ ii. salt to be made: barium sulphate reagent 1: aqueous potassium sulphate reagent 2: _________________ I could obtain solid barium sulphate crystals by: ___________________ iii. salt to be made: blue copper(II) sulphate crystals reagent 1: dilute sulphuric acid reagent 2: _________________ I could obtain blue copper(II) sulphate crystals by: __________________ 10b. Ammonium sulphate can be made by reacting aqueous ammonia with dilute sulphuric acid. 2NH3 (aq) + H2SO4 (aq) --> (NH4)2SO4 (aq) Calculate the mass of ammonium sulphate that can be made from 51 g of ammonia. Solution 10ai. reagent 2: aqueous lithium hydroxide Evaporating the salt solution to dryness to obtain lithium chloride crystals 10aii. reagent 2: aqueous barium chloride Filtration 10aiii. reagent 2: solid copper(II) oxide Crystallisation 10b. Mr of NH3 = 17 Mr of (NH 4 )2SO4 = 132no. of moles of NH3 = 51/17 = 3 no. of moles of (NH 4 )2SO4 = 1.5Mass of (NH 4 )2SO4 made = 1.5 x 132 = 198 g11. The table shows the soil pH ranges required by different crops for growth.
a. A farmer plants peanut and millet crops. Only the peanut crop grows well. Predict the pH of the soil b. Which other crop is most likely to grow well in the same soil c. The farmer adds calcium hydroxide, Ca(OH)2, and ammonium sulphate, (NH4)2SO4, to the soil. Explain the purpose of using each compound. d. A reaction occurs between calcium hydroxide and ammonium sulphate. i. complete the equation for this reaction. Ca(OH)2 + (NH4)2SO4 ----> ___________ + __________ + 2H2O ii. Explain why the farmer should not have added these two compounds to the soil at the same time. Solution 11a. 5.0 - 5.5 11b. Mango crop 11c. Ca(OH)2 is a weak alkali so it neutralises the acidic soil by reacting with H+ ions in the soil. Ca(OH)2 (s) + 2H+ ----> Ca2+ (aq) + 2H2O (l) (NH4)2SO4 serves as a nitrogenous fertiliser to increase the nitrogen content of the soil. 11di. Ca(OH)2 + (NH4)2SO4 ----> CaSO4 + 2NH3 + 2H2O 11dii. Ammonium compounds that make up fertilisers react with alkali, calcium hydroxide under the heat of the sun to release ammonia gas. The nitrogen content of the soil decreases as nitrogen is lost from the soil into the atmosphere. 2NH4+ (aq) + Ca(OH)2 (s) ----> 2NH3 (g) + Ca2+ (aq) + 2H2O (l) |
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