Railway Science (Chemistry-Acid ,Bases and Salt)

Total Questions: 50

31. In general, the oxides of metals are ______ in nature. [RRC Group D 13/09/2022 (Evening)]

Correct Answer: (a) basic
Solution:

When a Non-Metal reacts with Oxygen, it gives Oxide which on dissolution with water gives an acid. Properties of Non-Metals - Poor conductors of electricity and heat, Non-Ductile, High electronegative elements, Great oxidizing agents etc.
When a metal reacts with oxygen, it gives Metallic Oxide which on dissolution with water gives bases. Properties of Metals-Density and melting point is high, Ductile, low electronegativities, Good reducing agents etc. Examples of bases : Zinc hydroxide Zn(OH)₂ and copper oxide (CuO).

32. The acid and base which form sodium hydrogen carbonate are: [RRC Group D 15/09/2022 (Evening)]

Correct Answer: (a) H₂CO₃ and NaOH
Solution:

The acid and base used are Sodium Hydroxide ( NaOH ) and Hydrogen carbonate ( H₂CO₃) and the pH (8.3). Sodium hydroxide carbonate (sodium bicarbonate - Baking soda) - NaHCO₃ .
Reaction: (NaHCO₃). NaOH + H₂CO₃ ⟶ NaHCO₃+ H₂O. A Buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. HCI and NaCI as well as H₂CO₃ and Na₂CO₃ can be used as a buffer.

33. Which of the following is used to detect the presence of starch in food? [RRC Group D 17/09/2022 (Evening)]

Correct Answer: (d) Iodine solution
Solution:

Food items like rice, potato, bread, etc - rich in starch. After adding a few drops of dilute iodine solution to the sample of these food items, it develops a deep blue or blue-black colour. This confirms the presence of starch in the sample.
Solution and Use: Litmus solution (a type of dye) acts as an indicator for acidic and basic solutions. Naturally purple in colour but with acids turns red and with bases turns blue.
It is extracted from Lichen. Phenolphthalein (a colourless, weak acid) used as an indicator in titration experiments to indicate the endpoint of the titration.

34. Red cabbage is a natural indicator which gives different colour when mixed with an acid or a base. Identify the change in colour when it is mixed with an alkaline solution. [RRC Group D 17/09/2022 (Evening)]

Correct Answer: (c) Bluish green
Solution:

A purple solution (Red cabbage Indicator) determines the product is acidic or basic. A solution that serves as a pH indicator can be made using red cabbage. Flavin (anthocyanin) - A pigment molecule found in cabbage that reacts with acidity to change the color. The purple solution changes colour to red when it reacts with an acid and when it reacts with the base, changing colour to bluish-green.

35. Which of the following statements is true for a solution with high concentration of hydroxide ions? [RRC Group D 18/09/2022 (Morning)]

Correct Answer: (a) Solution is basic with high pH value.
Solution:

In an aqueous solution, the strong acid dissociates and releases more cationic hydrogen H⁺ ions so the pH ranges between 0 - 3. In an aqueous solution, the strong bases dissociate completely and release hydroxide OH⁻ ions, therefore pH ranges between 12 - 14.

36. A salt is dissolved in water and the pH of this salt solution is measured with a universal indicator paper. If the pH of solution is more than 7, the salt is most likely to be- [RRC Group D 19/09/2022 (Morning)]

Correct Answer: (c) K₂CO₃
Solution:

A white salt, soluble in water (insoluble in ethanol) which forms a strongly alkaline solution, basic in nature. NH₄CI(Ammonium Chloride) - pH = <7, Na₂SO₄ (Sodium sulphate) - pH = <7. KCl ( Potassium chloride) - pH = 7.
The strength of acids and bases depends on the number of H⁺ ions and OH⁻ ions produced respectively. Salts of strong acid and strong base form neutral solutions while salts of weak acid/base and strong base/acid are basic and acidic respectively in nature.

37. Which of the following solutions will turn pH paper blue? [RRC Group D 26/09/2022 (Evening)]

Correct Answer: (c) Sodium hydroxide
Solution:

(NaOH, basic solution). Litmus paper turns into blue when it is dipped in a basic solution. Sodium hydroxide gives Na⁺ and OH⁻ . The compound which gives OHions is considered as base. Lemon Juice : pH - 2-3, Gastric Juice : 1.5 - 2.5, Hydrochloric Acid (HCl) : pH - 2, All of these substances come under the acidic category. They turn the blue litmus paper into red when litmus paper comes in contact with them.

38. What will be the colour of pH paper when it is dipped in gastric juice? [RRC Group D 28/09/2022 (Afternoon)]

Correct Answer: (a) Red
Solution:

{acidic in nature, pH value (1.5-2.0), HCl (hydrochloric acid) is an important component in gastric juice} is colorless. The blue paper turns red when the pH is acidic and the red paper turns blue when the pH is alkaline. Neutral doesn't result in any change of color.Litmus paper determines only if the substance is acidic or alkaline while the pH paper determines the pH value.

39. Which of the following statements is/are incorrect? [RRC Group D 29/09/2022 (Evening)]

A) Oxides of metals are basic and that of non-metals are acidic in nature.
B) Oxides of metals are acidic and that of non-metals are basic in nature.
C) Non-metals are electronegative in nature while metals are electropositive in nature.

Correct Answer: (a) Only B
Solution:

Metallic Oxides - That contain at least one metal and one oxygen atom. They can be either ionic or covalent, but most are ionic. Non-metallic Oxides - That contain at least one non-metal and one oxygen atom. They can be either ionic or covalent, but most are covalent. Non-metals are generally electronegative in nature because these metal hydroxides release OH⁻ ions in solution.

40. pH paper shows light blue colour when dipped into milk of magnesia. This indicates that milk of magnesia is: [RRC Group D 29/09/2022 (Evening)]

Correct Answer: (a) A mild base
Solution:

Magnesium hydroxide {Mg(OH)₂} is named Milk of Magnesia. In general, magnesium salts react with alkaline water to form magnesium oxide as a precipitate. A pH paper is a piece of paper used to find out if a solution is basic, acidic or neutral. This is determined by dipping part of the paper into a solution and observing the colour change. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under alkaline conditions.