[CHEM] Chapter 7.1 - Acid _ Bases

1 DARRELL ER (COPYRIGHTED) TOPIC 7.1: ACID & BASES DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Very important chapter that is needed for Salts & QA • 4 key concepts: Acids, Bases, pH & indicators • 2 advanced concepts: Strength/Concentration/Basicity & Base vs Alkaline • Commonly tested every year Need to know relevant chemical and ionic equations (not going through in detail here, will focus on equations for “Chemical Equations” chapter instead) • Medium overall weightage • Constitute to 6% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 ACIDIC PROPERTIES ACID’S CHEMICAL REACTIONS STRENGTH, CONCENTRATION, BASICITY KEY CONCEPTS DARRELL ER (COPYRIGHTED) ©

What makes a compound/substance an ‘acid’? A compound is considered as an ‘acid’ due to the ability to dissociate H+ ions when they are dissolved in water. For example, HCl(l) in liquid state is called hydrogen chloride. (not acid yet) HCl(aq) in aqueous state is called hydrochloric acid. Hydrogen Chloride Hydrochloric Acid This is because when HCl dissolves in water, it dissociates to produce H+ ions which classifies it as an acid. HCl (aq)  H+ (aq) + Cl- (aq) In other words, an acid is only considered as an acid after it has been dissolved in water! 4 ACIDS Physical properties of acids 1) Acids tastes sour. 2) Dilute acids are irritants and will result in rashes and blisters. 3) Acids has the ability to change the colour of indicators, turning blue litmus paper to red. Examples of acids: Hydrochloric acid, HCl Sulfuric acid, H2SO4 Nitric acid, HNO3 Phosphoric acid, H3PO4 Hydrofluoric acid, HF Hydrobromic acid, HBr *Aqueous refers to a compound being in a solution. In other words, water is added. DARRELL ER (COPYRIGHTED) © Cl Cl Cl- Cl- H H H + H +

5 3 CHEMICAL REACTIONS ACID + METAL ACID + BASE ACID + CARBONATE 1) ACID + METAL  SALT + HYDROGEN GAS For example, H2SO4 + Mg  MgSO4 + H2 In order to test for hydrogen gas, use a lighted splint, it should extinguish with ‘pop’ sound. 2) ACID + BASE  SALT + WATER For example, H2SO4 + MgO  MgSO4 + H2O This is also known as a neutralisation reaction. 3) ACID + CARBONATE  SALT + WATER + CARBON DIOXIDE For example, H2SO4 + MgCO3  MgSO4 + H2O + CO2 In order to test for carbon dioxide gas, bubble the carbon dioxide gas into limewater, Ca(OH)2, a white precipitate will be formed. 1) ACID + METAL  SALT + HYDROGEN GAS 2) ACID + BASE  SALT + WATER 3) ACID + CARBONATE  SALT + WATER + CARBON DIOXIDE GAS DARRELL ER (COPYRIGHTED) ©

6 What is the relationship between the 3? STRENGTH CONCENTRATION BASICITY Let’s understand how all 3 are distinct yet related. Let’s run through each of them individually and keep it simple. ADVANCED CONCEPT DARRELL ER (COPYRIGHT