Railway Science (Chemistry-Acid ,Bases and Salt) (Part-II)

Total Questions: 50

31. The pH of the solutions are given. Which of the solutions has the highest concentration of hydrogen ions? [RRB Group D 18/09/2018 (Morning)]

Correct Answer: (c) 2.4
Solution:

The pH level (ranges from 0 to 14) is a measure of the number of Hydrogen ions in a solution. The lower the solution on the pH scale, the higher will be the concentration of hydrogen ions. pH value of 7 (water) is considered neutral, pH value greater than 7 is Basic and pH value less than 7 is Acidic. Important pH values: Acid rain (less than 5.6), Milk (6.5 - 6.8), Milk of Magnesia (10), Lemon juice (2.2), Pure blood (7.4).

32. Which of the following compounds does NOT possess water of crystallisation? [RRB Group D 18/09/2018 (Morning)]

Correct Answer: (d) Baking soda
Solution:

Water of crystallization is the fixed number of water molecules present in one formula unit of a salt. Compounds possess water of crystallization and their Chemical formula: Gypsum (CaSO₄.2H₂O), Washing soda (Na₂CO₃ .10H₂O), Copper sulphate (CuSO₄ , 5H₂O).

33. 5-8% of acetic acid is called: [RRB Group D 18/09/2018 (Morning)]

Correct Answer: (b) vinegar
Solution:

Vinegar is a diluted form of acetic acid that is commonly used in cooking and food preparation. Ester (General formula: –COO–R) : is a different chemical compound formed by the reaction between an alcohol and an organic acid. Ethanol (C₂H₅OH) : A renewable fuel made from corn and other plant materials. Glacial acetic acid refers to pure, concentrated acetic acid without any water content. Chemical Formula of acetic acid (ethanoic acid): CH₃COOH.

34. The pH values of three solutions X, Y and Z are 2, 11 and 7 respectively. Arrange them in descending order of hydrogen ion concentration. [RRB Group D 18/09/2018 (Evening)]

Correct Answer: (b) X, Z, Y
Solution:

The pH of a solution is a measure of the concentration of hydrogen ions (H⁺) in the solution. The lower the pH value, the higher the hydrogen ion concentration. A decrease in pH below 7 shows an increase in acidity (hydrogen ions), while an increase in pH above 7 shows an increase in alkalinity (hydroxyl ions).

35. The substances whose smell changes in acidic or alkaline medium are called _______. [RRB Group D 19/09/2018 (Morning)]

Correct Answer: (b) olfactory indicator
Solution:

Olfactory indicators are substances whose odour changes in acidic or basic medium. These substances are often used in qualitative analysis to detect the presence of acidic or basic solutions based on changes in smell. Examples : Onion, vanilla extract and clove oil. Example of other Indicators : Natural indicators (Litmus, turmeric), Synthetic indicators (methyl orange, phenolphthalein).

36. Tooth decay starts when the pH of the mouth is: [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (c) less than 5.5
Solution:

If we do not clean our teeth and mouth after eating, many harmful bacteria also begin to live and grow in it. These bacteria break down the sugars present from the leftover food and release acids. The acids gradually damage the teeth. This is called tooth decay. Chocolates, sweets, soft drinks and other sugar products are the major culprits of tooth decay.

37. As the pH value increases from 7 to 14, it represents: [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (b) an increase in the OH⁻ ion concentration
Solution:

pH or potential of hydrogen ion is a scale used to determine the hydrogen ion (H+) concentration in a solution. Its scale determines the acidity or basicity of the solution, ranging from 0 to 14, with 7 being neutral. pHs less than 7 are acidic while pHs greater than 7 are alkaline (basic).

38. ______ oxides react with acids as well as bases. [RRB Group D 19/09/2018 (Evening)]

Correct Answer: (d) Amphoteric
Solution:

Some metal oxides, such as aluminum oxide, zinc oxide, etc., show both acidic as well as basic behavior. Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.

39. Which of the following acids gives less 𝐻⁺ ions when dissolved in water ? [RRB Group D 19/09/2018 (Evening)]

Correct Answer: (c) acetic acid
Solution:

Acetic acid (CH₃COOH) is a weak acid, meaning it partially dissociates in water to produce fewer hydrogen ions (H⁺) compared to strong acids like hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃), which fully dissociate in water to produce more hydrogen ions.

40. The pH value of solution A is 6, the pH value of solution B is 8 and the pH value of solution C is 2. Which solution has the highest concentration of hydrogen ions? [RRB Group D 22/09/2018 (Morning)]

Correct Answer: (a) C
Solution:

The pH level is a measure of the number of Hydrogen ions in a solution. The lower the solution or compound on the pH scale, the higher will be the concentration of hydrogen ions. Therefore the solution having a pH of 2 i.e., Solution C will have the highest concentration of hydrogen ions.