Acid, Base and Salts RRB PYQ

Common salt can be used as the raw material for making all of the options listed. It is a key ingredient in the production of baking soda (sodium bicarbonate), sodium hydroxide (caustic soda), and bleaching powder (calcium hypochlorite). Each of these products is derived from salt through various chemical processes.

Bases do not turn blue litmus to red, unlike acids which can. Acids turn blue litmus to red, while bases turn red litmus to blue. Bases react with acids to form salts, essentially neutralizing them. Bases have a bitter taste, whereas acids have a sour taste. On the pH scale from 0 to 14, pH less than 7 indicates an acid, above 7 indicates a base, and pH 7 is neutral.

Plaster of Paris is chemically known as calcium sulphate hemihydrate: CaSO4·(1/2)H2O. It is produced by heating gypsum (calcium sulphate dihydrate) to about 150°C. When mixed with water, it rehydrates and forms a hard solid, making it useful for medical casts, sculptures, and construction. It is widely used for making casts and setting properties and ease of use.

When the pH of rainwater falls below 5.6, it is commonly referred to as acid rain. Normal rainwater has a pH of around 5.6 due to the natural presence of carbon dioxide forming weak carbonic acid. When the pH drops below 5.6, due to pollutants like sulfur dioxide and nitrogen oxides mixing with rainwater, it becomes more acidic.

In a universal indicator, the red color shows a pH of 0 to 3, meaning the substance is strongly acidic. A universal indicator helps us understand how acidic or basic a substance is by changing color. It's a mix of different indicators that show various colors depending on the pH level. For example, a neutral solution turns green, an acidic solution turns yellow, orange, or red, and a basic solution turns blue, purple, or violet, with the exact color depending on the pH value.

The reaction between sodium sulfate and barium chloride to form barium sulfate and sodium chloride is an example of a double displacement reaction. This reaction involves the mutual exchange of ions between the two reacting compounds, where the sodium ions (Na+) pair with chloride ions (Cl-) and barium ions (Ba2+) pair with sulfate ions (SO4^2-). It is characterized by the formation of an insoluble white precipitate of barium sulfate, which settles at the bottom of the test tube during the process.

CO2 gas turns lime water milky. The chemical formula for lime water is Ca(OH)2. When CO2 is added to lime water, Calcium Carbonate is formed which forms a milky solution in water: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l). Thus, CO2 gas turns lime water milky due to the formation of Calcium Carbonate.

When washing soda (sodium carbonate decahydrate, Na2CO3·10H2O) is exposed to a hot atmosphere, it begins to lose water molecules. This process is called efflorescence, where hydrated salts release water into the air. As a result, washing soda becomes powdery and turns into anhydrous sodium carbonate (Na2CO3). This is a physical change, where the crystalline structure changes due to the loss of water, but the chemical composition of the salt remains the same.

The pH of a solution containing significant concentrations of H+ ions is less than 7. The pH of a solution is a measure of its acidity or alkalinity. The pH scale ranges from 0 to 14. pH less than 7 indicates an acidic solution, while pH greater than 7 indicates a basic or alkaline solution. Since the question refers to a solution containing significant concentrations of H+ ions, it would suggest an acidic solution, which would have a pH less than 7.

The litmus paper test is used to determine if a solution is acidic or basic. Litmus paper, made from lichens by treating paper with natural dyes, serves as a type of pH paper. Blue litmus paper turns red or pink when it contacts an acidic solution with a pH below 4.5. It becomes purple if the solution's pH is between 4.5 and 8.3, and it stays blue if the pH is above 8.3.