Test: Acids, Bases and Salts - SSC CGL MCQ

Bases are typically characterized by a bitter taste. This taste distinction, along with their slippery feel when in solution, helps differentiate bases from acids. For instance, substances like baking soda are classified as bases due to their bitter taste.

In the Arrhenius concept, a base is defined as a substance that can release OH- ions in water. Examples of bases based on this definition include sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH), which can both release hydroxide ions in aqueous solutions.

The Bronsted-Lowry concept of acids and bases revolves around the idea that an acid is a substance capable of donating a proton, while a base is a substance capable of accepting a proton. This concept expands the definition of acids and bases beyond the simple release of ions in solution.

Acid-base indicators are crucial in distinguishing between acids and bases in a solution primarily through a color change. When an indicator is added to a solution with an acid or base, it changes color based on the pH of the solution. This color change helps in identifying whether the solution is acidic or basic, providing a visual cue for the nature of the substance in question.

Phenolphthalein is not recommended for weak bases like ammonium hydroxide, and methyl orange is unsuitable for weak acids such as acetic acid. This limitation arises because these indicators do not provide distinct color changes in the presence of weak acids or bases, making them less effective in such scenarios.

The pH scale is instrumental in quantifying the acidity or basicity of solutions. It provides a numerical value that indicates the concentration of hydrogen ions in a solution, which in turn signifies the strength of the acid or base. Lower pH values denote acidic solutions, while higher pH values indicate basic solutions.

The pH value of a liquid indicates its acidity or basicity level. This value is a measure of how acidic or basic a substance is on a scale from 0 to 14. Substances with a pH less than 7 are considered acidic, while those with a pH greater than 7 are basic. A pH of 7 is neutral. pH plays a critical role in various biological and chemical processes and is crucial for the survival of plants, animals, and even humans.

Plants and animals usually require a specific pH level to survive, which typically falls within the range of 7.0 to 7.8. This range provides the optimal conditions for various biochemical processes within organisms. Any significant deviation from this range can have detrimental effects on the health and well-being of plants and animals.

The formula to calculate the pH of a liquid is pH = -log [H+]. This formula represents the negative logarithm (base 10) of the hydrogen ion concentration in moles per liter. By calculating the pH value using this formula, one can determine whether a substance is acidic, basic, or neutral based on its pH value.

Neutralization is the chemical reaction that occurs when an acid and a base are mixed in the right proportions. This reaction results in the formation of salt and water, along with the release of heat. It is an essential concept in chemistry, demonstrating the balance of acidic and basic properties to create a neutralized solution.

Normal salts like sodium chloride and sodium nitrate do not contain replaceable hydrogen or hydroxyl groups. They are formed from the reaction of a base with an acid where both hydrogen and hydroxyl groups are not involved in the reaction, resulting in a simple salt compound.

When salts resulting from a weak acid and a weak base undergo hydrolysis in water, they produce a neutral solution. An example of this is ammonium acetate, which originates from acetic acid and ammonium hydroxide, leading to a solution that is neither acidic nor basic but neutral.

In the Lewis concept, acids are substances that can accept an electron pair, while bases are substances that can donate an electron pair. This distinguishes Lewis acids like boron fluoride (BF3) and aluminium chloride (AlCl3) from Lewis bases like fluoride ions (F−) and water.

Natural indicators like turmeric, litmus (from lichens), and China rose petals are derived from plant sources, making them organic and environmentally friendly. In contrast, synthetic indicators such as methyl orange and phenolphthalein are artificially created in laboratories to exhibit specific color changes in the presence of acids or bases. The choice between natural and synthetic indicators often depends on the specific requirements of the experiment or test being conducted.

Buffer solutions are special solutions that are known for their ability to resist significant changes in pH when small amounts of acids or bases are added to them. These solutions have specific pH values and are crucial in maintaining the stability of pH in various biological and chemical systems. Buffer solutions play a vital role in regulating pH levels and preventing drastic shifts in acidity or basicity, ensuring that processes can function optimally.