Tiêu đề Acid Basics and salts.pdf ✅

Acids, Bases & Salts ACIDS BASES SALTS Neutralisation In Water Acids react with metal carbonates or bicarbonates to form salt and water with the evolution of carbon dioxide gas. For Example: 1. Hydrochloric acid reacts with sodium carbonate to form sodium chloride and water with the release of carbon dioxide gas. Na2CO3(s) + 2 HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l) ii. Similarly, sodium bicarbonate also reacts with hydrochloric acid to form sodium chloride and water with the release of carbon dioxide gas. NaHCO3(s) + HCl (aq) → NaCl (aq) + CO2(g) + H2O(l) The reaction between an acid and a base to form salt and water is called a neutralisation reaction. For example: Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water. HCl + NaOH → NaCl + H2O Acids: An acid is a substance which dissociates (or ionises) when dissolved in water to release hydrogen ions. For Example: An aqueous solution of hydrochloric acid dissociates to form hydrogen ions. Since hydrogen ions do not exist as H+ in solution, they combine with polar water molecules to form hydronium ions. [H3O + ]. HCl (aq) → H+ (aq) + Cl- (aq) H+ + H2O → H3O + The presence of hydrogen ions [H+ ] in hydrochloric acid solution makes it behave like an acid. Acids react with metallic oxides to form salt and water. For Example: Copper oxide (II), a black metal oxide reacts with dilute hydrochloric acid to form a blue- green coloured copper chloride (II) solution. CuO + 2HCl → CuCl2(aq) + H2O Acids react with metals to produce salt by displacing hydrogen. For Example: 1. When dilute sulphuric acid reacts with the metal zinc, zinc sulphate is formed with the evolution of hydrogen gas. Zn + H2SO4 → ZnSO4 + H2 2. Zinc is the only metal which reacts with sodium hydroxide to form sodium zincate with the release of hydrogen gas. Zn + 2NaOH → Na2ZnO2 + H2 Reaction of Metallic Oxides Reaction with Metal Carbonates & Bicarbonates Reaction with Metals Baking Soda Plaster of Paris Water Of Crystallisation Bleaching Powder Reaction of Non- Common Salt Metallic Oxides Importance of pH in everyday life In Water Universal Indicator Bases react with non-metallic oxides to form salt and water. For Example: Calcium hydroxide reacts with non-metallic oxides like carbon dioxide to form calcium carbonate salt and water. Ca(OH)2 + CO2 → CaCO3 + H2O o Our body works well within a narrow pH range of 7.0 to 7.8. o When the pH of rain water is less than 5.6, it is known as acid rain. o To get rid of this pain, bases called antacids are used. o Antacids are a group of mild bases which react with the excess acid and neutralise it. o Commonly used antacids are magnesium hydroxide [Mg(OH)2] & sodium bicarbonate[NaHCO3] Tooth decay starts when the pH in the mouth falls below 5.5. o Tooth enamel is made up of calcium phosphate which is the hardest substance in the body. In case of a colourless liquid, the accurate pH can be obtained by adding a universal indicator. It is a mixture of several indicators and shows different colours at different concentration of hydrogen ions in a solution. For Example: o A universal indicator produces green colour in a neutral solution, pH = 7. o The colour changes from blue to violet as pH increases from 7 to 14. o The colour changes from yellow to pink and then to red as pH decreases from 7 to 1. A base is a substance which dissolves in water to produce hydroxide ions [OH- ions]. Bases which are soluble in water are called alkalis. For Example: Sodium hydroxide dissolves in water to produce hydroxide and sodium ions. NaOH (aq) → Na+ (aq) + OH- (aq) The presence of hydroxide ions [OH- ] in sodium hydroxide solution makes it behave like a base. Chemical formula: NaHCO3 It is produced on a large scale by treating cold and concentrated solution of sodium chloride (brine) with ammonia and carbon dioxide. NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3 On heating, it decomposes to give sodium carbonate with the evolution of carbon dioxide. 2NaHCO3 Na2CO3 + H2O + CO2 Uses Used as an antacid to treat acidity of the stomach. Used to make baking powder, which is used in preparation of cakes, breads, etc. Used in soda-acid fire extinguishers. Water molecules which form a part of the structure of a crystal are called water of crystallisation. The salts which contain water of crystallisation are called hydrated salts. Every hydrated salt has a fixed number of molecules of crystallisation in its one formula unit. For Example: CuSO4.5H2O, Na2CO3.10H2O, CaSO4.5H2O, and FeSO4.7H2O Copper sulphate crystals (CuSO4.5H2O) are blue in colour, and on heating strongly they lose all the water of crystallisation and form anhydrous copper sulphate, which is white. On adding water to anhydrous copper sulphate, it gets hydrated and turns blue. CuSO4.5H2O →CuSO4 + 5H2O CuSO4 + 5H2O→ CuSO4.5H2O Plaster of Paris is prepared by heating gypsum at 373 K. On heating, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.1/2 H2O) which is called Plaster of Paris. CaSO4.2H2O CaSO4. 1⁄2 H2O + 1 1⁄2 H2O Gypsum Plaster of Paris Uses Used in hospitals as plaster for supporting fractured bones in the right position. Used as a fire-proofing material. Chemical name: Sodium chloride Common salt is a neutral salt and can be prepared in the laboratory by the reaction of sodium hydroxide and hydrochloric acid. NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(aq) It is an important raw material for products of daily use such as NaOH, baking soda, washing soda and bleaching powder. Bleaching powder is manufactured from chlorine gas. It is produced by the action of chlorine on dry slaked lime [Ca(OH)2]. Ca(OH)2 + Cl2 → CaOCl2 + H2O It is represented as CaOCl2 Uses: For bleaching cotton and linen in the textile industry and for bleaching wood pulp in the paper industry. Used for disinfecting drinking water to make it free of germs. Understand the chemistry and remember the equations