Acid, Base and Salts RRB PYQ

Sodium chloride (NaCl) produces a neutral solution because it is a salt formed from a strong acid (HCl) and a strong base (NaOH). When dissolved in water, the ions of a neutral salt do not react with water (hydrolysis), keeping the pH at approximately 7. If a salt is formed from a strong acid and a weak base, the solution will be acidic; if it's from a weak acid and a strong base, the solution will be basic.

An acid does not release OH- ions in water. An acid is a substance that releases hydrogen ions when dissolved in water or donates protons. A base, conversely, is the substance that releases hydroxide ions in water.

When a solution is diluted with water, the concentration of hydroxide ions (OH-) decreases. The initial pH of 8 indicates a basic solution, meaning it has more OH- ions than H+ ions. Adding water reduces the concentration of OH- ions, thereby increasing the concentration of H+ ions relative to OH- ions. As a result, the pH decreases, making the solution less basic and close to neutrality. Dilution generally leads to a reduction in ion concentration, thereby affecting the pH.

The reaction Ca(OH)2 + Cl2 → CaOCl2 + H2O leads to the production of bleaching powder. Bleaching powder is a chemical compound widely used as a disinfectant, bleaching agent, and in water purification processes. Bleaching powder contains chlorine in the form of calcium oxychloride, which is responsible for its bleaching and disinfecting action.

Limewater is a common name for a diluted solution of calcium hydroxide in water. It is known for its slightly basic properties and is used in various applications, including water treatment and as a test for carbon dioxide. Limewater is used in a process known as lime softening to reduce water hardness. It is also used as a neutralizing agent in municipal waste water treatment.

In chemical industries, bleaching powder acts mainly as an oxidising agent due to the release of nascent oxygen when it reacts with acids. Known chemically as calcium oxychloride, it is produced by the action of chlorine gas on dry slaked lime. Its ability to remove color from materials like wood pulp, cotton, and linen is a result of the oxidation of colored substances into colorless ones. Due to its strong oxidizing nature, it is also widely used for disinfecting drinking water by killing harmful germs and bacteria.

According to the Brønsted-Lowry theory, an acid donates a proton. This theory is broader than Arrhenius' theory because it doesn't require the acid or base to be in aqueous solution. This theory is more general than Arrhenius theory and works in non-aqueous solvents.

Bleaching powder is chemically known as calcium hypochlorite (Ca(OCl)2). It is prepared by the reaction of chlorine gas (Cl2) with dry calcium hydroxide (Ca(OH)2). The chemical reaction for the preparation is: 2Ca(OH)2 + 2Cl2 → Ca(ClO)2 + CaCl2 + 2H2O. Bleaching powder is commonly used to disinfect drinking water and as a bleaching agent in the textile and paper industries.

The pH of a neutral solution at 25°C is 7. This is because the concentrations of hydrogen ions and hydroxide ions are equal. The pH of a neutral solution can change with temperature because the concentration of hydrogen ions and hydroxide ions in water varies with temperature, as the equilibrium between water dissociation changes with temperature, leading to more hydrogen ions being produced.

Ethanol (C2H5OH) is not a base, as it does not contribute to increasing the concentration of hydroxide ions in a solution. It is commonly used as a solvent and in alcoholic beverages. Instead, it is a neutral organic compound with no basic characteristics, distinguishing it from KOH, NH4OH, and NaOH, which are all bases.