[CHEM] Chapter 7.2 - Salts

1 DARRELL ER (COPYRIGHTED) © TOPIC 7.2: SALTS DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Complex chapter • Salt preparation requires high level of mastery • Requires strong knowledge from Acid & Bases • Very important chapter for Qualitative Analysis • Light-Medium overall weightage • Constitute to 3.5% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 OXIDES NEUTRALISATION APPLICATION OF NEUTRALISATION KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

4 4 TYPES OF OXIDES BASIC OXIDE ACIDIC OXIDE AMPHOTERIC OXIDE NEUTRAL OXIDE DARRELL ER (COPYRIGHTED) ©

5 OXIDES SUMMARY TABLE Oxides Basic Oxides Acidic Oxides Amphoteric Oxides Neutral Oxides Element type Metal oxides Non-metal oxides Some metal oxides Some non-metal oxides Chemical properties Behaves like an alkali, neutralise with acid Behaves like an acid, neutralise with alkali Can behave like an acid or an alkali, can react with both acid and alkali Does not react Examples - Sodium oxide - Potassium oxide - Calcium oxide - Carbon dioxide - Sulfur dioxide - Phosphorus (V) oxide - Aluminium oxide, Al2O3 - Lead (II) oxide, PbO - Zinc oxide, ZnO - Water, H2O - Carbon monoxide, CO - Nitrogen monoxide, NO DARRELL ER (COPYRIGHTED) ©

6 NEUTRALISATION NEUTRALISATION Neutralisation is the process where acid reacts with a base to produce salt & water. ACID + BASE  SALT + WATER REAL-LIFE APPLICATIONS - Regulating the pH of soil Farmers will add bases like slaked lime (calcium hydroxide) or quicklime (calcium oxide) to ensure the soil maintains the optimal pH for growth of plants. - Treating indigestion Overeating can result in the overproduction of hydrochloric acid by our stomach, causing indigestion. In order to neutralise the excess hydrochloric acid, we would need to intake antacid (a type of base). - Toothpaste Bacteria on our teeth produce acids which can result in tooth decay. Toothpastes contain magnesium hydroxide help to remove bacteria & neutralise the acids in our mouth. DARRELL ER (COPYRIGHTED) ©

7 SALT SOLUBILITY TABLE ACID + EXCESS INSOLUBLE SUBSTANCE TITRATION PRECIPITATION KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

8 SALT SOLUBILITY TABLE SUMMARY TABLE Soluble salts Insoluble salts SPA - Sodium - Potassium - Ammonium ALL NONE Nitrates ALL NONE Chlorides ALL except Lead(II) chloride, PbCl2 Silver chloride, AgCl Sulfates ALL except Lead(II) sulfate, PbSO4 Barium sulfate, BaSO4 Calcium sulfate, CaSO4 Carbonates SPA salts ALL except Oxides & Hydroxides Group I & some Group II elements ALL except Ba, Ca (oxide / hydroxide) are slightly soluble. SPA Anything with sodium, potassium & ammonium are definitely soluble. All Group I metals form soluble salts. (Sodium, Potassium…) *Find your own method for memorising. Make your life easier by finding a methodology that works for you! DARRELL ER (COPYRIGHTED) ©

9 UNDERSTANDING SALT PREPARATION VS MEMORISING Due to the seemingly complex nature of salt preparation, many students opt to memorise the procedure for salt preparation and attempt regurgitate the content in exams. While that might work to an extent, they will not be able to solve application questions and might remember some parts wrongly. In this upcoming section, I will attempt to break down the logic behind salt preparation and show you why you do not need to memorise anything once you have understood salt preparation. *If you find the next couple of slides too complicated, feel free to skip to SLIDE 20. DARRELL ER (COPYRIGHTED) ©

10 3 methods ACID + INSOUBLE SUBSTANCE TITRATION PRECIPITATION There are only 3 ways to prepare a salt. Choosing which method to use depends on the solubility of the salt and the solubility of the reagents. Use the table above to see how each preparation method is different! DARRELL ER (COPYRIGHTED) © NAME REACTION PRECIPITATION SOLUBLE + SOLUBLE  INSOLUBLE SALT ACID + INSOLUBLE SUBSTANCE SOLUBLE + INSOLUBLE  SOLUBLE SALT TITRATION SOLUBLE + SOLUBLE  SOLUBLE SALT