CHAPTER 8 SALTS. NaCl. A salt is an ionic substance produced when the hydrogen ion of the acid is replaced by metal ion or an ammonium ion.

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1 CHAPTER 8 SALTS A salt is an ionic substance produced when the hydrogen ion of the acid is replaced by metal ion or an ammonium ion. The salt consists of two parts, cation from base and anion from acid. NaOH (Base) NaCl HCl (Acid) 148

2 Complete the table below. Table of Metal ion Sulphate salt (SO4 2- ) Chloride salt (Cl - ) Nitrate salt (NO3 - ) Carbonate salt (CO3 2- ) K + K2SO4 KCl KNO3 K2CO3 Na + Ca 2+ Mg 2+ Al 3+ Zn 2+ Fe 2+ Sn 2+ Pb 2+ Cu 2+ Ag + NH4 + Ba 2+ Based on the table above, mark the insoluble salt. 149

3 SOLUBLE & INSOLUBLE SALTS SALT SOLUBLE INSOLUBLE K +, Na +, NH4 + All soluble none Nitrate salts (NO3 - ) Chloride salts (Cl - ) Sulphate salts (SO4 2- ) Carbonate salts (CO3 2- ) Oxide salts (O 2- ) Hydroxide salts (OH - ) All nitrate salts All chloride salts All sulphate salts Sodium carbonate, Na2CO3 Potassium carbonate, K2CO3 Ammonium carbonate, (NH4)2CO3 Sodium oxide, Na2O Potassium oxide, K2O Calcium oxide, CaO (slightly soluble) Sodium hydroxide, NaOH Potassium hydroxide, KOH Calcium hydroxide, Ca(OH)2 (slightly soluble) none Lead (II) chloride, PbCl2 Silver chloride, AgCl Mercury chloride, HgCl Lead (II) sulphate Calcium sulphate Barium sulphate All others carbonate salts All oxide salts All hydroxide salts 150

Eg: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) [write the step of preparation of the salts on the

4 Preparation and Purification of Soluble Soluble salt can be prepared by the following ways: 1. Reaction between acid and alkali - preparation for sodium, potassium and ammonium salts only. Eg: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) [write the step of preparation of the salts on the diagram] Burette HCl solution NaCl solution Evaporating dish NaOH solution NaCl crystal salt NaCl salt crystal 151

Reaction between acid and metal Eg: H2SO4(aq) + Zn (s) ZnSO4(aq) + H2 (g) 3.

[write the step of preparation of the salts on the diagram] Copper(II) nitrate Solution + excess

5 Preparation and Purification of Soluble Soluble salt can be prepared by the following ways: 1. Reaction between acid and metal oxide Eg: HNO3(aq) + MgO(s) Mg(NO3)2 (aq) + H2O(l) 2. Reaction between acid and metal Eg: H2SO4(aq) + Zn (s) ZnSO4(aq) + H2 (g) 3. Reaction between acid and metal carbonate Eg: HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l) [write the step of preparation of the salts on the diagram] Copper(II) nitrate Solution + excess CuO heat heat Copper(II) nitrate solution Evaporating Dish Copper(II) nitrate solution & crystal salt Cu(NO 3 ) 2 crystal salt 152

6 Crystallization is a process to crystallize the soluble salts. Recrystallization process will carried out in order to get pure and more defined crystal Physical characteristic of crystals Fixed geometrical shapes such as a cuboids, rhombic or prism Flat surface, straight edges and sharp angles. Same shapes for same substance but differ in sizes Fixes angle between two neighbouring surfaces. 153

7 Preparation of insoluble salts An insoluble salt is prepared through precipitation method. Aqueous solution of two soluble salts are mixed to form insoluble and soluble salt: [write the general equation of preparation insoluble salt] The reaction is called double decomposition. Two solutions contain ions that make up the insoluble salts. Eg: Preparation of lead(ii) iodide salt by using lead(ii) nitrate solution and potassium iodide solution. [write the balance chemical equation] Double Decomposition 154

8 Chemical and Ionic Equation Chemical and ionic equation can be written for all reaction That used to prepare salts. Example: Formation of precipitate Barium Sulphate, BaSO4. 1. : BaCl2 (aq) + Na2SO4 (aq) BaSO4(s) + 2NaCl (aq) 2. Ionic Equation: Ionic equation shows the ions take part in the reaction. Exercise 1. Change each of the following word equations to a balanced chemical equation. a) Sulphuric acid + zinc zinc sulphate + hydrogen gas. b) Silver nitrate + potassium iodide silver iodide + potassium nitrate c) Nitric acid + chromium(iii) hydroxide chromium(iii) nitrate + water 155

9 2. Complete the following equations. a) HCl (aq) + NiO (s) b) HNO3 (aq) + Ca(OH)2 (aq) c) H2SO4 (aq) + MgCO3 (s) 3. Write an ionic equation for each reaction between the following pairs of substances. a) Sulphuric acid, H2SO4 and barium hydroxide, Ba(OH)2 solution b) Ammonium chloride, NH4Cl solution and silver nitrate, AgNO3 solution. c) Lead(II) nitrate, Pb(NO3)2 solution and copper(ii) sulphate, CuSO4 solution. d) Iron(III) oxide, Fe2O3 and hydrochloric acid, HCl. 156

10 Constructing Ionic Equation using the Continuous Variation Method Continuous variation method can be used to construct ionic equation for the formation of insoluble salts. Fixed volume of a reactant A is react with varying volumes of a reactant B to determine the mole ratio of reactant A that react completely with reactant B. If x mol of reactant A with y mole of reactant B, than the empirical formula for insoluble salt is A x B y. Example: 2Fe 3+ (aq) + 3CO3 2- (aq) Fe2(CO3)3 (s) 157

11 158

12 Example cm 3 of 0.2 mol dm -3 X n+ solution reacts completely with 4.0 cm 3 of 0.1 mol dm -3 Y m- solution to form a salt XmYn. Write the ionic equation and hence determine the empirical formula of the salt reaction cm 3 of 0.1 mol dm -3 solution of P x+ ions reacts completely with 9.0 cm 3 of 0.1 mol dm -3 solution of Q y- ions to form a salt PyQx. Write the ionic equation and hence determine the empirical formula of the salt in this reaction. 159

13 Solving Problem Involving Calculation of Quantities of Reactants or Product in Stoichiometric Reactions Since the quantities of chemicals involved in a reaction are in term of moles, the quantities of chemicals (volume, mass and number of particles) must be converted to moles in calculation regarding quantities of reactant and products. Exercise 1. Calculate the number of moles of aluminium sulphate produced by the reaction of 0.2 mole of sulphuric acid with excess aluminium oxide. [0.067 mole] g of sodium hydroxide reacts with excess sulphuric acid. What is the mass of sodium sulphate produces [RAM: H,1 ; O,16 ; Na,23 ; S,32] [ 3.55 g] 160

14 3. What the volume of carbon dioxide gas evolved at s.t.p when 2.1 g of magnesium carbonate reacts with excess nitric acid. [ RAM: C,12;O,16;Mg,24; s.t.p = 22.4 dm 3 ] [ 560 cm 3 ] 4. What is the mass of magnesium required to react with 20 cm 3 of 2.0 mol dm 3 hydrochloric acid to produce 120 cm 3 of hydrogen at temperature? [RAM: Mg,24 ; 1 mol = 24 dm 3 at room temp.] [ 0.12 g] 161

Observations on the physical properties of salts Qualitative Analysis of General procedure of qualitative analysis Action of heat on salts Tests for cations and anions Colour & Solubility of the Salt

15 Observations on the physical properties of salts Qualitative Analysis of General procedure of qualitative analysis Action of heat on salts Tests for cations and anions Colour & Solubility of the Salt Confirmatory tests for cations and anions GREEN PALE GREEN Iron(II) Sulphate, FeSO 4 Iron(II) Nitrate, Fe(NO 3 ) 2 Iron(II) Chloride, FeCl 2 BROWN YELLOW/BROWN [depend on concentration] Iron(III) Sulphate, Fe 2 (SO 4 ) 3 Iron(III) Nitrate, Fe(NO 3 ) 3 Iron(III) Chloride, FeCl 3 REDDISH-BROWN INSOLUBLE GREEN INSOLUBLE Iron(III) Oxide, Fe 2 O 3 Copper(II) Carbonate, CuCO 3 BLUE BLUE BLACK INSOLUBLE Copper(II) Sulphate, CuSO 4 Copper(II) Nitrate, Cu(NO 3 ) 2 Copper(II) Chloride, CuCl 2 Copper(II) Oxide, CuO 162

16 Colour & Solubility of the Salt WHITE COLOURLESS WHITE INSOLUBLE Potassium Oxide, K 2 O Sodium Oxide, Na 2 O Calcium Oxide, CaO Magnesium Oxide, MgO Aluminium Oxide, Al 2 O 3 WHITE [cold] YELLOW [cold] INSOLUBLE INSOLUBLE YELLOW [hot] BROWN [hot] Zinc Oxide, ZnO Lead(II) Oxide, PbO 163

17 Gas test Oxygen gas hydrogen gas Wooden splinter Oxygen gas, O 2 Hydrogen gas, H 2 Carbon dioxide gas sulphur dioxide gas Carbon dioxide Sulphur dioxide HCl acid HCl acid Sodium Sulphite, Na 2 SO 3 Sodium Carbonate, Na 2 CO 3 Red litmus paper chlorine gas Glass rod dipped into concentrated HCl acid ammonia gas White fumes Chlorine gas, Cl 2 Ammonia gas, NH 3 164

18 Carbonate salts EFFECT OF HEAT ON SALTS Sodium carbonate & potassium carbonate are very stable. They do not decompose on heating. Carbonate Salt Metal Oxide + Carbon dioxide Carbonate salts 1. Calcium carbonate 2. Magnesium carbonate 3. Aluminium carbonate Carbonate salts [ yellow hot ] [ white cold ] 1. Zinc carbonate 165

19 Carbonate Salt Metal Oxide + Carbon dioxide Carbonate salts [ brown ] [ brown ] 1. Iron(III) carbonate Carbonate salts [ green ] [ black ] 1. Copper(II) carbonate Carbonate salts [ brown hot ] [ yellow cold ] 1. Lead(II) carbonate 166

20 Carbonate Salt Metal + Carbon dioxide + Oxygen gas Carbonate salts [ grey ] 1. Mercury(II) carbonate Carbonate salts [ shiny grey ] 1. Silver carbonate Carbonate salts [ golden yellow ] 1. Aurum(II) carbonate 167

21 nitrate salts Nitrate Salt Metal Oxide + Oxygen gas + Nitrogen dioxide nitrate salts 1. Calcium nitrate 2. Magnesium nitrate 3. Aluminium nitrate nitrate salts [ yellow hot ] [ white cold ] 1. Zinc nitrate 168

22 Nitrate Salt Metal Oxide + Oxygen gas + Nitrogen dioxide nitrate salts [ brown ] [ brown ] 1. Iron(III) nitrate nitrate salts [ blue ] [ black ] 1. Copper(II) nitrate nitrate salts [ brown hot ] [ yellow cold ] 1. Lead(II) nitrate 169

23 Nitrate Salt Metal + Nitrogen dioxide + Oxygen gas nitrate salts [ grey ] 1. Mercury(II) nitrate nitrate salts [ shiny grey ] 1. Silver nitrate Nitrate Salt Metal nitrite + Oxygen gas nitrate salts 1. Potassium nitrate 2. Sodium nitrate 170

24 TEST FOR ANIONS Unknown aqueous salt solution Salt needed to be dissolved into water first to produce aqueous salt solution. [ state the procedure ] [ state the procedure ] [ state the procedure ] [ state the procedure ] OBSERVATION OBSERVATION OBSERVATION OBSERVATION [ label the diagram ] [ label the diagram ] [ label the diagram ] [ label the diagram ] Ionic Equation Ionic Equation Ionic Equation Ionic Equation CONCLUSION CONCLUSION CONCLUSION CONCLUSION [ state the anion ] [ state the anion ] [ state the anion ] [ state the anion ] 171

25 TEST FOR CATIONS Unknown aqueous salt solution Add NaOH drop by drop Salt needed to be dissolved into water (soluble salts) or in dilute acid then filtered (insoluble salts) first to produce aqueous salt solution. No precipitate White precipitate Coloured precipitate Green Add NaOH drop by drop until excess Brown Dissolve in excess NaOH Insoluble in excess NaOH Blue * All coloured ions insoluble in excess NaOH 172

26 TEST FOR CATIONS Unknown aqueous salt solution Add NH 3 drop by drop Salt needed to be dissolved into water (soluble salts) or in dilute acid then filtered (insoluble salts) first to produce aqueous salt solution. No precipitate White precipitate Coloured precipitate Green Add NH 3 drop by drop until excess Brown Dissolve in excess NH 3 Insoluble in excess NH 3 Blue Dissolved in excess NH 3 Dark blue solution * Fe 2+ & Fe 3+ ions insoluble in excess NH 3 173

27 Confirmatory Test for Cation Cation Procedure Observation Fe 2+ Fe 3+ Pb 2+ NH 4 + Exercise 1. Identify the aqueous solutions based on the test and observation given. a. Potassium thiocyanate, KSCN, solution is added. b. Potassium iodide, KI, solution is added. c. Ammonia solution, NH3, is added until excess. d. A little hydrochloric acid is added. e. A sulphuric acid, iron(ii) sulphate solution and concentrated sulphuric acid is added. f. Ammonia solution is added until excess. Type Observation Answer Blood red solution formed. Yellow precipitate is formed. Blue precipitate dissolve to form dark blue solution. Effervescene occur and lime water turn into chalky. Brown ring formed. White precipitate dissolved. K 2 CO 3 ZnCl 2 PbCl 2 CuSO 4 NaNO 3 FeCl 3 174

Salts Soluble Insoluble Nitrate salts - All nitrate salts - Carbonate salts - Potassium carbonate, K 2 CO. Except

Salts Soluble Insoluble Nitrate salts - All nitrate salts - Carbonate salts - Potassium carbonate, K 2 CO. Except Chapter 8: Salts 1. Salts - A salt is an ionic compound. - The anion part comes from the acid while the cation part comes from a base. - Example: KCl, KOH(aq) + HCl(aq) KCl(aq) + H 2 O(l) - A salt is a