Class 10 – Science Extra Questions – Ch. 2 – Acids Bases and Salts

Ans: A

Explanation: The pH scale ranges from 0 to 14. A pH of 7 is considered neutral. Substances with a pH less than 7 are acidic, and substances with a pH greater than 7 are alkaline (or basic). A pH of 2 is significantly less than 7, indicating that the substance is acidic. Soapy substances are typically alkaline.
Correct Option: A

Ans: A

Explanation: pH is a measure of the acidity or alkalinity of a solution. A strong acid has a low pH (typically below 7). When a strong acid is diluted with pure water, the concentration of hydrogen ions (H+) decreases. This decrease in H+ concentration leads to an increase in the pH of the solution. Pure water has a neutral pH of 7. As more water is added to the acid, the solution becomes less acidic and its pH moves closer to 7. Therefore, the pH increases.
Correct Option: A

Ans: C

Explanation: A weak acid is defined as an acid that dissociates only partially in water, meaning it does not fully ionize. Acetic acid (CH3COOH) is a weak acid because it only releases a small fraction of its hydrogen ions (H+) when dissolved in water. Option A is incorrect because an acidic solution is a characteristic of all acids, strong or weak. Option B is incorrect because high ionization is characteristic of strong acids. Option D is incorrect because the presence of a -COOH group is characteristic of carboxylic acids, which can be either strong or weak; the strength is determined by the degree of ionization.
Correct Option: C

Ans: B

Explanation: The question states that indigestion is caused by excess stomach acid and asks for a class of drugs that neutralizes stomach acid. Antacids are specifically designed to neutralize stomach acid. Antivirals treat viral infections, antifungals treat fungal infections, and anticoagulants prevent blood clotting. Therefore, antacids are the correct class of drugs.
Correct Option: B

Ans: B

Explanation: Plaster of Paris is a building material developed by heating gypsum, a sulfate mineral composed of calcium sulfate dihydrate (CaSO₄·2H₂O). When heated, gypsum loses one and a half molecules of water, forming calcium sulfate hemihydrate (CaSO₄·½H₂O). This hemihydrate is what is commonly known as plaster of Paris. When mixed with water, it rehydrates to form a solid matrix of gypsum.
Correct Option: B

Ans: B

Explanation: Carbonic acid is formed when carbon dioxide dissolves in water. This is what gives carbonated beverages their characteristic tangy flavor and effervescence. Boric acid is a mild antiseptic, sulfuric acid is a strong mineral acid and is corrosive, and oxalic acid is found in plants like rhubarb and can be toxic in large amounts. Therefore, carbonic acid is the acid responsible for the flavor in beverages.
Correct Option: B

Ans: C

Explanation: Citric acid is found in citrus fruits like oranges, lemons, and limes. Lactic acid is produced during the fermentation of milk, making it a key component of yogurt. Tartaric acid is naturally present in many fruits, including tamarind. Acetic acid is the main component of vinegar, which is produced by the fermentation of ethanol. While grapes contain tartaric acid, acetic acid is not their primary acidic component; rather, it’s found in vinegar derived from fermented sources, which can include grapes but the direct matching of acetic acid to grapes as its *common source* is less precise than the others.
Correct Option: C

Ans: A

Explanation: Hydrogenation of oils involves adding hydrogen gas across the carbon-carbon double bonds in unsaturated fatty acids, converting them into saturated fatty acids. This process requires hydrogen to react with these double bonds. Option A accurately describes this essential characteristic of hydrogen gas in this specific reaction. While hydrogen can act as a reducing agent (Option B), its specific reactivity with C=C bonds is the direct reason for its utility in hydrogenation. Option C describes a hazardous property and not the reason for its chemical utility. Option D is incorrect; hydrogen gas is a reactant, not a catalyst.
Correct Option: A

Ans: B

Explanation: The thick white and yellowish clouds of Venus are primarily composed of droplets of sulfuric acid. These clouds are a result of complex photochemistry involving sulfur dioxide and water vapor in Venus’s atmosphere. Acetic acid, nitric acid, and hydrochloric acid are not the primary components of these clouds.
Correct Option: B

Ans: B

Explanation: Acidity is typically associated with the ability of a substance to donate protons (H+) in a polar solvent like water, where these protons can be solvated. In non-polar solvents, ions are not readily formed or stabilized. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) are strong acids, meaning they dissociate readily in water. Acetic acid (CH3COOH) is a weak acid. While some degree of dissociation might occur, it would be significantly less pronounced in a non-polar solvent. However, the question asks which substance *would exhibit properties of acidity*. Some polar covalent molecules, when dissolved in non-polar solvents, can still exhibit acidic behavior due to intermolecular forces and slight polarity. Of the options provided, HCl is the most likely to exhibit some degree of acidic properties even in a non-polar solvent, although the extent of dissociation would be very low compared to its behavior in water. It’s important to note that “acidity” in non-polar solvents is a more nuanced concept and less pronounced than in polar solvents. However, compared to the other options, HCl is the strongest acid and thus most likely to show some characteristic acidic behavior.

Reconsidering the question: The core of acidity is the donation of a proton. This process is significantly hindered in non-polar solvents because the resulting ions are not stabilized. In a purely non-polar solvent, ionic dissociation is extremely difficult. Therefore, none of the substances would effectively exhibit typical acidic properties (like significant H+ donation or reaction with bases) in hexane. Acetic acid, being a weak acid in water, would be even weaker in hexane. HCl and H2SO4, while strong in water, would also undergo very little dissociation in hexane. Thus, the concept of “exhibiting properties of acidity” in a non-polar solvent for these compounds is highly limited.

Given the typical context of high school chemistry, where acidity is strongly tied to aqueous solutions and ion formation, and considering the extreme difficulty of ionic dissociation in a non-polar solvent like hexane, it’s most likely that none of the options will exhibit *significant* properties of acidity.

Correct Option: B