CBSE Class 10 Science Notes Chapter 2 Acids Bases And Salts:, Summaries of Family and Consumer Science

Download CBSE Class 10 Science Notes Chapter 2 Acids Bases And Salts: and more Summaries Family and Consumer Science in PDF only on Docsity! Class 10 Science Notes Chapter 2 Acids Bases And Salts: A salt is formed when hydrogen ions are replaced by a metal or an ammonium ion in an acid. A base is a material that reacts with an acid to produce just water and salt. When an acid reacts with a base, it produces a salt. Bases are commonly found in household cleansers that are used to remove oil from windows and floors, as well as soaps, toothpaste, egg whites, dishwashing liquids, and household ammonia. Introduction to Acids, Bases, and Salts A substance that tastes sour in water, turns blue litmus red and neutralizes bases is known as an acid. If a substance’s aqueous solution tastes bitter, turns red litmus blue, or neutralizes acids, it’s called a base. Salt is a neutral material that has no effect on litmus in an aqueous solution. Classification of matter On the basis of a) composition – elements, compounds, and mixtures b) state – solids, liquids, and gases c) solubility – suspensions, colloids, and solutions Types of mixtures – homogeneous and heterogeneous Types of compounds – covalent and ionic What Are an Acid and a Base? Ionizable and non-ionizable compounds An ionizable compound when dissolved in water or in its molten state dissociates into ions almost entirely. Examples: NaCl, HCl, KOH, etc. A non-ionizable compound does not dissociate into ions when dissolved in water or in its molten state. Examples: glucose, acetone, etc. Acids and Bases An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid. Acidic substances are usually identified by their sour taste. Arrhenius's theory of acids and bases Arrhenius acid – when dissolved in water, dissociates to give H+ (aq) or H3O+ ion. Arrhenius base – when dissolved in water, dissociates to give OH− ion. Examples Acids ● Hydrochloric acid (HCl) ● Sulphuric acid (H2SO4) ● Nitric acid (HNO3) Bases ● Sodium hydroxide (NaOH) ● Potassium hydroxide (KOH) ● Calcium hydroxide (Ca(OH)2) Bronsted Lowry theory A Bronsted acid is an H+ (aq) ion donor. A Bronsted base is an H+ (aq) ion acceptor. Example In the reaction: HCl (aq) + NH3 (aq) → NH+4(aq) + Cl− (aq) HCl – Bronsted acid and Cl−: its conjugate acid NH3 – Bronsted base and NH+4 : its conjugate acid Physical test Given are two possible physical tests to identify an acid or a base. a. Taste An acid tastes sour whereas a base tastes bitter. The method of taste is not advised as an acid or a base could be contaminated or corrosive. Example: The flavors of curd, lemon juice, orange juice, and vinegar are all sour. Because they contain acids, these compounds have a sour flavor. Baking soda has a sour flavor. It’s an example of a foundation. b. Effect on indicators by acids and bases An indicator is a chemical substance which shows a change in its physical properties, mainly color or odor when brought in contact with an acid or a base. Below mentioned are commonly used indicators and the different colors they exhibit: a) Litmus In a neutral solution – purple ● They are comprised of metal oxides, metal hydroxides, metal carbonates, and metal bicarbonates. ● Most of them are insoluble in water. Alkali: ● An alkali is an aqueous solution of a base, (mainly metallic hydroxides). ● It dissolves in water and dissociates to give OH− ion. ● All alkalis are bases, but not all bases are alkalis. Hydronium ion Hydronium ion is formed when a hydrogen ion accepts a lone pair of electrons from the oxygen atom of a water molecule, forming a coordinate covalent bond. Dilution Dilution is the process of reducing the concentration of a solution by adding more solvent (usually water) to it. It is a highly exothermic process. To dilute acid, the acid must be added to water and not the other way round. Strength of acids and bases Strong acid or base: When all molecules of a given amount of an acid or a base dissociate completely in water to furnish their respective ions, H+(aq) for acid and OH−(aq) for base). Weak acid or base: When only a few of the molecules of a given amount of an acid or a base dissociate in water to furnish their respective ions, H+(aq) for acid and OH−(aq) for base). Dilute acid: contains less number of H+(aq) ions per unit volume. Concentrated acid: contains more number of H+(aq) ions per unit volume. Universal indicator A universal indicator has a pH range from 0 to 14 that indicates the acidity or alkalinity of a solution. A neutral solution has pH=7 pH pH=−log10[H+] In pure water, [H+]=[OH−]=10−7 mol/L. Hence, the pH of pure water is 7. The pH scale ranges from 0 to 14. If pH < 7 → acidic solution If pH > 7→ basic solution c) Metallic salt + conc. sulphuric acid → salt + more volatile acid 2NaCl(aq) + H2SO4(aq) → Na2SO4(aq) + 2HCl(aq) 2KNO3(aq) + H2SO4(aq) → K2SO4(aq) + 2HNO3(aq) d) Metal + oxygen → metallic oxide (base) 4Na(s) + O2(g) → 2Na2O(s) 2Mg(s) + O2(g) → 2MgO(s) e) Metal + water → base or alkali + hydrogen Zn(s) + H2O(steam) → ZnO(s)+ H2(g) f) Few metallic oxides + water → alkali Na2O(s) + H2O(l) → 2NaOH(aq) g) Ammonia + water → ammonium hydroxide NH3(g) + H2O(l) → NH4OH(aq) Salts Salts A salt is a combination of an anion of an acid and a cation of a base. Examples – KCl, NaNO3, CaSO4, etc. Salts are usually prepared by the neutralization reaction of an acid and a base. Common salt Sodium Chloride (NaCl) is referred to as common salt because it’s used all over the world for cooking. Family of salts Salts having the same cation or anion belong to the same family. For example, NaCl, KCl, and LiCl. pH of salts A salt of a strong acid and a strong base will be neutral in nature. pH = 7 (approx.). A salt of a weak acid and a strong base will be basic in nature. pH > 7. A salt of a strong acid and a weak base will be acidic in nature. pH < 7. The pH of a salt of a weak acid and a weak base is determined by conducting a pH test. Chemicals from common salt Sodium chloride is a common salt. NaCl is its molecular formula. The fundamental element in our meals is sodium chloride. It is used in our food as a flavor enhancer as well as a preservative. From common salt, we may make the following four compounds. 1. Sodium hydroxide or lye or caustic soda 2. Baking soda or sodium hydrogen carbonate or sodium bicarbonate 3. Washing soda or sodium carbonate decahydrate 4. Bleaching powder or calcium hypochlorite Preparation of Sodium hydroxide The strong base sodium hydroxide is a common and useful one. Preparing a solution of sodium hydroxide (NaOH) in water requires extra caution because the exothermic reaction releases a lot of heat. It’s possible that the solution will spatter or boil. Here’s how to manufacture a sodium hydroxide solution safely, as well as recipes for a variety of NaOH strengths. Chemical formula – NaOH Also known as – caustic soda Preparation (Chlor-alkali process): Electrolysis of brine (solution of common salt, NaCl) is carried out. At anode: Cl2 is released At cathode: H2 is released Sodium hydroxide remains in the solution. Bleaching powder Bleaching powder is soluble in water and is used as a bleaching agent in textile industries. It is also used as an oxidizing agent and a disinfectant in many industries. It should also be noted that bleaching powder is synthesized by the reacting chlorine gas on dry slaked lime i.e. Ca(OH)2. Chemical formula – Ca(OCl)Cl or CaOCl2 Preparation – Ca(OH)2(aq)+Cl2(g)→CaOCl2(aq)+H2O(l) On interaction with water – bleaching powder releases chlorine which is responsible for bleaching action. Uses of Bleaching Powder ● It is used for bleaching dirty clothes in the laundry, and as a bleaching agent for cotton and linen in the textile industry. ● It is a strong oxidizing agent, hence used as an oxidizer in many industries. ● It is used as a disinfectant which is used for disinfecting water to make potable water. Baking soda Sodium bicarbonate, also known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3 and the IUPAC designation sodium hydrogen carbonate. A sodium cation (Na+) and a bicarbonate anion (HCO3) combine to form this salt. Sodium bicarbonate is a white, crystalline substance that is commonly found as a fine powder. It tastes slightly salty and alkaline, like washing soda (sodium carbonate). Chemical name – Sodium hydrogen carbonate Chemical formula – NaHCO3 Preparation (Solvay process): a. Limestone is heated: CaCO3→CaO+CO2 b. CO2 is passed through a concentrated solution of sodium chloride and ammonia: NaCl(aq)+NH3(g)+CO2(g)+H2O(l)→NaHCO3(aq)+NH4Cl(aq) Uses: ● Reduces the acidity in the stomach ● Acts as an antacid that is used to treat stomach upset and indigestion ● Used in the process of washing as a water softener Washing soda Chemical name – Sodium hydrogen carbonate Chemical formula – NaHCO3 Preparation (Solvay process) – a. Limestone is heated: CaCO3→ CaO + CO2 b. CO2 is passed through a concentrated solution of sodium chloride and ammonia: NaCl(aq) + NH3(g) + CO2(g) + H2O(l) → NaHCO3(aq) + NH4Cl(aq)