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

Total Questions: 50

11. When acid reacts with metal carbonate, ____________ is formed. [RRB JE 24/05/2019 (Morning)]

Correct Answer: (b) All of the options
Solution:

Example - 2HCl (Hydrochloric acid)+ MgCO₃ (Magnesium Carbonate) → MgCl₂ (Magnesium chloride) + CO₂ (Carbon dioxide) + H₂O (water). H₂SO₄ (Sulfuric acid) + FeCO₃ (Ferrous carbonate) → FeSO₄ (Ferrous sulfate) + H₂O (Water) + CO₂ (Carbon dioxide) .

12. A substance X turns the colour of red litmus blue, and it will change methyl orange- [RRB JE 24/05/2019 (Morning)]

Correct Answer: (a) Yellow
Solution:

Base turns the color of red litmus to blue. It means X is a base. In an acidic medium, methyl orange becomes red. Methyl Orange (C₁₄H₁₄N₃NaO₃S) is a weak acid that breaks down into orange neutral molecules when it comes into contact with water. The equilibrium is to the left in acidic conditions, and the concentration of neutral molecules is too poor to see the orange color. The presence of much water causes the red color of a faintly acid solution of methyl orange to become yellow, probably due to hydrolytic dissociation. Acid turns the color of blue litmus to red.

13. What is the colour of the base? [RRB JE 24/05/2019 (Afternoon)]

Correct Answer: (d) Pink with phenolphthalein and yellow with methyl orange
Solution:

It turns red in the presence of an acid and blue in the presence of a base. Phenolphthalein - It is a colorless indicator that turns pink in the presence of a base and remains colourless in the presence of an acid. Bromothymol blue - It is a pH indicator that turns yellow in the presence of an acid and blue in the presence of a base. Methyl orange - It is an indicator that changes from red in acidic solutions to yellow in basic solutions.

14. Which of the following is a weak base? [RRB JE 25/05/2019 (Morning)]

Correct Answer: (a) 𝑁𝐻₄OH
Solution:

Weak base - A base which is partially ionized in water to produce a small amount of OH⁻ ions. Example: Lead hydroxide Pb(OH)₂ , Aluminum hydroxide Al(OH)₃ . Strong Base - A base that is completely ionized in water to produce a large amount of OH⁻ ions. Examples - NaOH (Sodium Hydroxide), KOH (Potassium Hydroxide), Ca(OH)₂ (Calcium Hydroxide).

15. In universal indicators, red colour shows a pH of- [RRB JE 25/05/2019 (Evening)]

Correct Answer: (d) 0 to 3
Solution:

A universal indicator is a mixture of different types of indicators that exhibits different coloration at different levels. It is used to detect the acidic or basic nature of a substance or a solution. It can be in the form of a paper strip or a solution. Examples: Methyl red, and Phenolphthalein. It gives an orange or yellow color if the solution is a weak acid (pH: 3-6). It gives green color with a neutral solution (pH: 7), gives blue color with a weak base (pH: 8-11) and gives Indigo color with a strong base (pH > 11).

16. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solutions would reverse the change? [RRB JE 26/05/2019 (Evening)]

Correct Answer: (c) Hydrochloric acid
Solution:

Acids are sour in taste and change the blue litmus to red. Examples : Nitric acid, Sulphuric acid. Bases are bitter in taste and change the red litmus to blue. Examples: Ammonium hydroxide, Sodium hydroxide, Calcium hydroxide, Sodium bicarbonate (Baking soda). Litmus is a water-soluble mixture of different dyes extracted from lichens.

17. Acidic solutions in water conduct electricity because they produce- [RRB JE 26/05/2019 (Evening)]

Correct Answer: (c) Hydrogen ions
Solution:

The nucleus of a hydrogen atom that has been isolated from its electron. Acidic solutions - A solution that has a higher concentration of positively charged hydrogen ions (H⁺) than negatively charged hydroxide ions (OH⁻). Basic Solution - A solution that has a higher concentration of hydroxide ions. Neutral solution - A Solution that is neither acidic nor basic.

18. Oxides of non-metals are ______in nature. [RRB JE 27/05/2019 (Morning)]

Correct Answer: (b) Acidic
Solution:

Chemical compounds composed of oxygen combined with another element or elements. Example - (Carbon dioxide) CO₂ , (Sulphur dioxide) SO₂ , (Calcium oxide) CaO, (Carbon monoxide) CO, (Zinc Oxide) ZnO, (Barium peroxide) BaO₂ , (water) H₂O. Based on their acid-base characteristics oxides are classified as Acidic , Basic, Amphoteric and Neutral.

19. Which of the following gases causes acid rain along with sulfur dioxide and carbon monoxide ? [RRB JE 27/05/2019 (Morning)]

Correct Answer: (c) Nitrogen oxides
Solution:

Acid rain is rain when the pH of water drops below 5.6. It is formed high up in the atmosphere when SO₂ (sulphur dioxide) and NO₂ (Nitrogen oxides) combine with water, oxygen and other chemicals to form more acidic pollutants (sulfuric acid (H₂SO₄) and nitric acid (HNO₃). The major sources of SO₂ and NO₂ in the atmosphere are burning of fossil fuels like coal, gasoline and natural gas.

20. A basic solution changes the colour of turmeric indicator from- [RRB JE 28/05/2019 (Morning)]

Correct Answer: (c) Yellow to red
Solution:

(Due to the neutralization reaction). The turmeric is acidic in nature and it is yellow in color. When turmeric paste is added to the acidic solution, it remains unchanged. The color in the acidic solution is yellow. Litmus (a natural indicator) - Blue litmus paper turns red if the substance is acidic. Red litmus paper turns blue if the substance is basic or alkaline. A basic solution is a solution with pH value > 7. Turmeric is also a natural acid-base indicator. An acidic solution is a solution with pH value < 7.