AcidsBases and Salts

Acids and Bases Content The Reactivity Series Part 1: Acids Definition of Acids Physical Properties of Acids No. Property Explanation 1 Have a sour taste - 2 Dissolve in water to form solutions which conduct electricity (electrodes) - Presence of free and mobile ions to carry electrical charge 3 Turn moist blue litmus paper red - Note: Use the acronym: Popular Scientists Can Make A Zoo In The Lab However Cannot See God

Chemical Properties of an Acid No. Property Observations and test for gases (If any) 1 React with reactive metals to form a salt and hydrogen gas Observations - Effervescence observed - Colourless, odourless gas produced Test for Gas Produced (Hydrogen) - Place a lighted to the gas - Gas evolved extinguishes the lighted splint with a ‘pop’ sound - The gas is Hydrogen 2 React with hydrogen carbonates/carbonates to form a salt, carbon dioxide, and water Observations - Effervescence observed - Colourless, odourless gas produced Test for Gas Produced (Carbon Dioxide) - Bubble the gas through limewater - Gas evolved forms a white precipitate in limewater - The gas is Carbon Dioxide 3 React with Metal Oxides and Hydroxides to form a salt and water only (neutralisation) - 4 React with Aqueous Ammonia to form an Ammonium salt only - Why do acids not react with certain metals? Case no. Case 1 Unreactive Metal - When unreactive metals like Copper or Silver are added to dilute acids, there is no reaction 2 Initial Reaction, but stops shortly after - Metals like Lead will react with acids like Hydrochloric acid and Sulfuric acid in its initial reaction - However, the initial reaction forms a layer of insoluble <salt name> that does not dissolve in water - This prevents the metal from further reacting with the acid hence the reaction stops Role of Water in Acids - When acids are dissolved in water, they dissociate to form hydrogen ions. The hydrogen ions cause acids to be acidic therefore able to be involved in reactions

- When put in a non-aqueous solution, the acid molecules exist as covalent molecules. No dissociation occurs; therefore, no hydrogen ions are produced, therefore it does not display any acidic properties Uses of Acids Acid Use Sulfuric Acid Manufacture of fertilizers Manufacture of Detergents As battery acid in cars Hydrochloric Acid Cleaning impurities by removing rust or scale Ethanoic Acid Vinegar, Preservatives, and Flavour Enhancer Phosphoric Acid Giving a sour taste to beverages Basicity of an Acid - Basicity of an acid is the number of hydrogen ions which can be produced by one molecule of acid. - Acids like Hydrochloric Acid are monobasic, they dissociate to form 1 hydrogen ion per molecule. - Acids like Sulfuric Acid are dibasic, they dissociate to form 2 hydrogen ions per molecule - Acids like Phosphoric Acid are tribasic, they dissociate to form 3 hydrogen ions per molecule Monoacidic and Diacidic Bases - Acidity of a base is the number of hydroxide ions which can be produced by one molecule of a base - Bases like Sodium Hydroxide are monoacidic bases - Bases like Calcium Hydroxide are diacidic bases Part 2: Bases and Alkalis Properties of Alkalis No. Property Observations and Test for gases (If any) 1 Have a bitter taste and feel soapy -

2 Turn red litmus paper blue - 3 React with acids to form a salt and water only (neutralization) - 4 When gently warmed with ammonium salts, produce a salt, ammonia gas and water only Observations - Colourless, pungent gas produced Test for gas (Ammonia) - Place a piece of moist red litmus paper to the gas - Gas evolved will turn the moist red litmus paper blue - Gas is Ammonia 5 React with a solution containing one metal salt to give another metal salt and metal hydroxide - Uses of Bases and Alkalis Base/Alkali name Use Magnesium Oxide - Making refractory bricks Sodium Hydroxide and Potassium Hydroxide - Preparation of detergents Calcium Hydroxide - Reduce acidity in soils Ammonia solution - Making fertilizers Why are Ammonia and Calcium Hydroxide not added together to soil? - Both compounds will react to form ammonia gas, the nitrogen content decreases by ammonia gas, hence the plant will not grow well as nitrogen is lost. Part 3: Strength and Concentration Definitions of Strong and Weak Acids/Alkalis Definition of a Strong Acid/Alkali - Defined as an acid/alkali that is completely ionized in aqueous solution Definition of a Weak Acid - Defined as an acid/alkali that is partially ionized in aqueous solution Concentration vs Strength of an acid Strength Concentration Extent of ionisation How much of an acid is dissolved in a solution Part 4: The pH Scale Different Methods used to measure the pH of a chemical 1. Using a chemical compound known as an indicator Note: - The strength of an acid is NEVER affected by its concentration - Dilute Acid does not mean Weak Acid - A strong acid will always be fully ionised regardless of concentration

2. Using a data logger with a pH sensor/probe Common Indicators and their changes of colour Indicator Colour in acidic solution pH range in which colour change is observed Colour in alkaline solution Methyl Orange Red 3-5 Yellow Screened Methyl Orange Violet 3-5 Green Litmus Red 5-8 Blue Bromothymol blue Yellow 5-8 Blue Phenolphthalein Colourless 8-10 Pink Importance of pH in soil - It may be unsuitable for plant growth if the soil is too acidic or too alkaline Part 4: Oxides Acidic Oxides - Examples include Carbon Dioxide, Phosphorus Oxide, and Sulfur Trioxide Basic Oxides - Defined as an oxide that reacts with an acid to form a salt and water only - Examples include Copper (II) Oxide, Magnesium Oxide, and Calcium Oxide Amphoteric Oxides - Examples include Zinc Oxide, Aluminium Oxide, and Lead (II) Oxide Neutral Oxides - Examples are Carbon Monoxide and Nitric Oxide, and Water Appendix I: Acid Salts and Basic Salts Acid Salts - It is called an acidic salt as the hydrogen ions in the acid are not completely replaced by the metal cation or ammonium cation from the base or carbonate it reacts with. The pH of the solution is lower than 7 - Usually formed when a strong acid reacts with a weak base - Example include Sodium Bicarbonate and Sodium dihydrogen phosphate Basic Salts - Is called a basic salt as the hydroxide ions in the base are not completely replaced by the anion of the acid it reacts with. The solution has a pH more than 7 - Usually formed when a weak acid reacts with a strong base - Examples include Calcium Carbonate

Salts Part 1: Water of Crystallisation - Many salts combine with water molecules to form crystals - Are removed by evaporating the crystals to dryness - Can always be rehydrated. Part 2: Solubility of Salts Soluble Salts Insoluble Salts All Sodium salts All Potassium Salts All Ammonium salts All nitrates - All chlorides/iodides Lead (II) Chloride/ Iodide Silver Chloride/Iodide All sulfates Barium Sulfate Lead (II) Sulfate Calcium Sulfate Sodium Carbonate/ Sodium Hydroxide Potassium Carbonate/ Potassium Hydroxide Ammonium Carbonate/ Aqueous Ammonia All Carbonates and Bases Part 3: Making Salts Section A: Titration (Both starting materials are soluble) How to carry out Titration? Diagram Steps 1. Pipette 25.0𝑐𝑚3 of acid into a conical flask 2. Add a few drops of indicator into the conical flask 3. Add the alkali drop by drop slowly until the indicator turns from <initial color> to <final color> permanently 4. Record the volume of alkali needed to completely react with the acid 5. Repeat the experiment using 25.0𝑐𝑚3 of acid and the recorded volume of alkali without indicator 6. Heat to evaporate the water until saturated 7. Cool until <salt name> crystals can form 8. Filter and dry <salt name> crystals between shee