AISS 2024 Salts Notes

6092 Chemistry 1 AISS Chemistry Unit Chapter 12: Salts Name: …………………………………….( ) Class: …….. Date: ………………. ___________________________________________________________________ 12.1 What is a Salt? Based on your knowledge on the chemical reactions in the chapter of acids and bases, state the possible reactions that would allow you to prepare a salt. • Acid + metal → salt + hydrogen gas 2HCl + Zn → ZnCl2 + H2 • Acid + base → salt + water H2SO4 + 2NH3 → (NH4)2SO4 • Acid + metal carbonate → salt + carbon dioxide + water 2HNO3 + CaCO3 → Ca(NO3)2 + CO2 + H2O A salt is a compound formed when the hydrogen ion in an acid is replaced by a metallic ion or an ammonium ion. Reactions in Which Salts Can Be Made Possible reactants Salt formed Metal/ Carbonate (for the cation) Acid (for the anion) zinc (Zn) hydrochloric acid (HCl) Zinc chloride (ZnCl2) copper(II) carbonate (CuCO3) Nitric acid (HNO3) copper(II) nitrate Cu(NO3)2 At the end of this section, you should be able to: • define a salt • state common reactions used to prepare a salt • describe the general rules for the solubility of common salts in water

6092 Chemistry 2 Magnesium (Mg) / Magnesium carbonate (MgCO3) sulfuric acid (H2SO4) magnesium sulfate (MgSO4) aqueous ammonia NH3(aq) sulfuric acid (H2SO4) Ammonium chloride NH4Cl potassium hydroxide (KOH) Phosphoric acid (H3PO4) potassium phosphate (K3PO4) Checkpoint 1 State possible starting reactants for the following salts based on the above chemical acid/base reactions. No Reactants Products (Salts) 1 Copper(II) oxide/hydroxide/carbonate + nitric acid copper(II) nitrate 2 Sodium oxide/hydroxide/carbonate + hydrochloric acid sodium chloride 3 Potassium oxide/hydroxide/carbonate + sulfuric acid potassium sulfate 4 Zinc/zinc oxide/hydroxide/carbonate + hydrochloric acid zinc chloride 5 magnesium/magnesium oxide/hydroxide/carbonate + nitric acid magnesium nitrate

6092 Chemistry 3 12.2 General rules for the solubility of common salts in water Do ionic compounds dissolve in water? …………………………………………………………………………………………………………. The table below summarises the general rules for solubility of the common salts in water at room temperature. Soluble salts Insoluble salts All sodium, potassium, ammonium salts (SPA) All nitrates All Chlorides (Clown Laugh & Smile) except Lead chloride, PbCl2 Silver chloride, AgCl All Sulfates (Super Big Chicken Leg) except Barium sulfate, BaSO4 Calcium sulfate, CaSO4 Lead sulfate, PbSO4 Sodium carbonate, Na2CO3 Potassium carbonate, K2CO3 Ammonium carbonate, (NH4)2CO3 except All carbonates Sodium hydroxide, NaOH Potassium hydroxide, KOH Ammonium hydroxide, NH4OH except All hydroxides Calcium hydroxide, Ca(OH)2 is slightly soluble Sodium oxide, Na2O Potassium oxide, K2O except All oxides Calcium oxide, CaO is slightly soluble The solubility of a salt must be determined before we can choose a suitable method for preparing the salt. Yes. Water molecules are attracted to ions. This weakens the electrostatic forces between the ions. The ions are pulled from the lattice structure and the compound dissolves to form aqueous solution. However, solubility in water is dependent on temperature and nature of solute as well. Not salts, these are bases.

6092 Chemistry 4 12.3 Water of Crystallisation • Salts crystals are often formed by crystallisation from aqueous solutions, and thus often have water molecules bonded to them. This water is known as water of crystallisation. • Salts that contain water of crystallisation are known as hydrated salts. • Heating a hydrated salt drives away the water, leaving the anhydrous salt. Examples of salts containing water of crystallisation hydrated salt → anhydrous salt + water heat Checkpoint 2 State the solubility of the following salts/bases. No Salts Solubility (Soluble/Insoluble) 1 copper(II) nitrate Soluble 2 sodium chloride Soluble 3 barium sulfate Insoluble 4 zinc chloride Soluble 5 magnesium hydroxide Insoluble

6092 Chemistry 5 12.4 Preparation of Salts Recall: Solubility table The method of preparation depends on three factors: (a) Solubility of the salt (b) Reactivity of the metal (c) Chemicals being reacted together to make the salt

6092 Chemistry 6 12.4.1 Preparation of Soluble Salts • The following are different ways to prepare a soluble salt. 1. Reaction between an acid and excess of an insoluble solid: a) Reacting an acid with an insoluble carbonate b) Reacting an acid with an insoluble base c) Reacting an acid with a metal • Never use reactive metals , e.g. sodium, potassium, as the reaction is highly dangerous. • Never use unreactive metals e.g. copper, gold, silver, platinum • Only moderately reactive metals such as magnesium, zinc are suitable for this method. 2. Titration a) Reacting an acid with an alkali (soluble base) b) Reacting an acid with a soluble carbonate (SPA carbonate) (1) Reacting an acid with an insoluble carbonate E.g. Preparation of pure and dry copper(II) sulfate, CuSO4 crystals Step 1 Identify solubility of salt Copper(II) sulfate, CuSO4, is soluble in water (Not SPA) Step 2 Identify the appropriate method Thought process: 1. How do I decide the acid to be used? ……………………………………………………………………………. ……………………………………………………………………………. 2. Why can’t a metal be used to prepare this salt? ……………………………………………………………………………. ……………………………………………………………………………. At the end of this section 2, you should be able to: • Correlate practical experiment to the chemical equation and state symbols • Understand the rationale of the steps to prepare soluble and insoluble salts • Suggest suitable separation techniques to obtain soluble and insoluble salts • Suggest suitable reactants to obtain soluble and insoluble salt • Acid to be used is decided by identity of the anion of the salt. Acid → sulfuric acid Copper is an unreactive metal, so copper will not react with acid to form salt. Other unreactive metals include, silver, gold and platinum

6092 Chemistry 7 3. Can an insoluble base be used to prepare this salt? If yes, give the possible insoluble bases. ……………………………………………………………………………. ……………………………………………………………………………. Write the balanced chemical equations , with state symbols for the possible reactants used with acid to prepare copper(II) sulfate. (1) ……………………………………………………………………… (2) ……………………………………………………………………… (3) ……………………………………………………………………… Step 3 Prepare the salt by following the steps Teacher can choose to do demonstration or play video in class. →copper(II) carbonate + sulfuric acid Step 1: Fill half a beaker with dilute sulfuric acid. With constant stirring, add solid copper(II) carbonate until no more copper(II) carbonate can be dissolved. See Think Before addition of chemicals: Colour and state of (Appearance) • Sulfuric acid: colourless solution • Copper(II) carbonate: green solid Copper is a transition metal, forming coloured compounds Copper(II) oxide Copper(II) hydroxide Copper(II) carbonate CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g) Cu(OH)2 + H2SO4(aq) → CuSO4(aq) + 2H2O(l)

6092 Chemistry 8 During the addition of chemicals, what do you observed? 1. effervescence is observed 2. Green solid dissolved as it is added 3. Colourless solution turns blue 4. Colour of blue litmus paper (turns red) Excess insoluble solid added 1. Effervescence 2. Green solid could no longer dissolve → implies excess insoluble solid 3. Colour of blue litmus paper • Production of CO2 • All copper(II) carbonate reacts with the sulfuric acid to form c