Acid, Base and Salts RRB PYQ

The reaction between silver nitrate and sodium chloride to form silver chloride and sodium nitrate is an example of a double displacement reaction. This reaction involves the exchange of ions between the two aqueous reactants: the silver ions (Ag+) pair with chloride ions (Cl-) and sodium ions (Na+) pair with nitrate ions (NO3-). A key feature of this specific reaction is the formation of a white precipitate of silver chloride (AgCl), which is insoluble in water. The remaining product, sodium nitrate, stays dissolved in the solution, making this a classic example of a precipitation reaction.

The Contact Process is used for the manufacturing of sulphuric acid. Burning sulphur to form sulphur dioxide (SO2): S + O2 → SO2. Oxidation of SO2 to SO3 using a vanadium (V) oxide catalyst: 2SO2 + O2 → 2SO3. SO3 is absorbed in concentrated H2SO4 to form oleum, which is then diluted to make sulphuric acid.

Bleaching powder is chemically known as calcium hypochlorite, with the formula Ca(OCl)2. The reactants used for its production are calcium hydroxide (Ca(OH)2) and chlorine gas (Cl2). The chemical reaction for the production of bleaching powder is: 2Ca(OH)2 + 2Cl2 → Ca(ClO)2 + CaCl2 + 2H2O.

Baking soda is pure sodium bicarbonate (NaHCO3), while baking powder blends sodium bicarbonate with a dry acid (commonly tartaric acid or cream of tartar) plus a moisture-absorbing filler like starch. Baking soda needs an external acidic ingredient (e.g., buttermilk, lemon juice) to release CO2 for leavening; baking powder already contains the acid, so it produces CO2 when moistened and heated. Baking powder is typically 'double-acting,' giving off some CO2 at room temperature and more during baking, whereas baking soda reacts only once, immediately after it meets an acid and liquid.

When metals react with acids, they typically produce hydrogen gas as one of the products. This reaction is a common example of a single displacement or substitution reaction, where the metal displaces hydrogen ions from the acid, resulting in the formation of a salt and the release of hydrogen gas. Hydrogen gas is colorless and odorless, making it difficult to detect without proper equipment.

Statements 1 and 2 are correct because a precipitation reaction is defined by the formation of an insoluble solid when two aqueous solutions are mixed. Precipitation reactions typically involve ionic salts reacting through double displacement, whereas reactions involving only acids and bases are called neutralisation reactions. These reactions occur when the attraction between certain ions in a solution is stronger than their attraction to water molecules, causing them to bond and 'fall out' of the solution.

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.

Washing soda is chemically known as sodium carbonate decahydrate, represented as Na2CO3·10H2O. The compound contains 10 water molecules of crystallization, hence the value of 'x' is 10. It is commonly used in cleaning products and as a water softener. The presence of water of crystallization in washing soda makes it efflorescent, meaning it can lose water molecules when exposed to air.

30 ml NaOH will be required to neutralise 15 ml of HNO3. This is calculated using the concept of neutralization and proportionality. 20 ml of NaOH neutralizes 10 ml of HNO3; so the ratio is NaOH/HNO3 = 20/10 = 2. Now, for 15 ml of HNO3, NaOH = 2 x 15 = 30 ml.

Ammonium hydroxide (NH4OH) is a weak base because it does not fully dissociate into its ions in an aqueous solution. A weak base is a base that is partially ionized in water, producing a small amount of OH- ions. Examples include NH4OH and Mg(OH)2. A strong base is a base that is completely ionized in water, producing a large amount of OH- ions. Examples include NaOH and KOH.