Acid, Base and Salts RRB PYQ

Carbon dioxide gas is passed through calcium hydroxide to form calcium carbonate and water. This reaction is generally used in the limewater test, which helps detect the presence of CO2. Helium gas is an inert gas, while oxygen gas does not form calcium carbonate with calcium hydroxide. Hydrogen gas does not react with calcium hydroxide.

A solution is considered alkaline if its pH is greater than 7. pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration: pH = -log10([H+]). For [H+] = 1×10^-4 Mol/l, pH ≈ 4, which is less than 7, so this solution is acidic. For [H+] < 1×10^-7 Mol/l, a lower hydrogen ion concentration indicates a higher pH; since the comparison is less than a very small value (1×10^-7), we can infer the pH is greater than 7, so this solution is alkaline.

Baking soda is chemically known as Sodium bicarbonate. It is widely used in baking as a leavening agent, in cleaning, and for antacid purposes. Its chemical properties—ability to release CO2, neutralize acids, and act as a mild base—make it extremely useful in everyday life.

Sodium carbonate (Na2CO3) is a salt formed from a strong base (NaOH) and a weak acid (H2CO3). When it is dissolved in water, it undergoes hydrolysis, producing sodium hydroxide (NaOH) and carbonic acid (H2CO3). Since NaOH is a strong base and dominates the reaction, the solution becomes basic in nature. As a result, the solution has a pH greater than 7.

On the pH scale, a dark blue colour usually indicates a strong base (alkaline solution). A strong basic solution has a pH between 12 and 14. Examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH) solutions. Acids are shown by red/orange, neutral by green, and weak bases by lighter blue.

In chemistry, bases exhibit distinct color changes when mixed with certain indicators. When phenolphthalein is added to a basic solution, it turns pink; this is because phenolphthalein is colourless in acidic or neutral conditions but changes to pink in alkaline (basic) conditions. On the other hand, when methyl orange is added to a base, it turns yellow. Methyl orange is typically red in acidic conditions and changes to yellow as the solution becomes more alkaline. These colour changes help chemists determine whether a substance is acidic or basic and are commonly used in titration experiments to identify the endpoint.

Acids are compounds that, when dissolved in water, form free hydrogen ions (H+ ions). When bases are dissolved in water, they form hydroxyl ions (OH-). The pH scale is used to determine the acidity or basicity of an acid or base, going from 0 to 14. pH indicators are made up of several chemical compounds known as universal indicators, which are used to measure the exact pH.

The atmosphere of Venus is notably covered by thick, opaque clouds composed primarily of droplets of sulphuric acid. These clouds are responsible for the planet's characteristic yellowish-white appearance and its high reflectivity. While the bulk of Venus's atmosphere is carbon dioxide (96.5%), its upper cloud deck is dominated by concentrated sulphuric acid. Sulphuric acid is formed photochemically when sunlight triggers reactions between sulphur dioxide and water vapour in the upper atmosphere. Despite being further from the Sun than Mercury, Venus is the hottest planet in the solar system due to a runaway greenhouse effect caused by its dense carbon dioxide atmosphere.

A pH of 11 indicates that the substance is basic or alkaline. A substance with a pH of 11 is alkaline, meaning it has more OH- ions than H+ ions. Such a basic solution will change red litmus paper to blue, unlike neutral or acidic solutions.

The pH range of a strongly acidic solution is 0-3. A strongly acidic solution has a very low pH, typically between 0 and 3. These solutions have a high concentration of hydrogen ions. Examples include hydrochloric acid or sulfuric acid in high concentrations.