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

Total Questions: 50

1. The concentration of __________ in pure water is: [RRB Group D 27/09/2018 (Afternoon)]

Correct Answer: (c) H⁺ and OH⁻ are similar ions.
Solution:

Pure water has the highest concentration of water molecules. The water potential of pure water is always taken as zero at standard temperature and pressure. When some solute is dissolved in water, the water potential of pure water decreases. The pH of a solution is a measure of the concentration of hydrogen ions in solution. The pH of pure water is 7.

2. The pH of ______ CANNOT be found directly using pH paper. [RRB Group D 27/09/2018 (Evening)]

Correct Answer: (c) solid sodium bicarbonate
Solution:

pH (power of hydrogen) - Measurement of acidity and basicity of solution. Range : 0 - 14 (7 being neutral, less than 7 indicate acidity, whereas greater than 7 indicates a base). Litmus paper - An indicator which tells if a substance is an acid or a base.

3. ____ is not acidic. [RRB Group D 28/09/2018 (Morning)]

Correct Answer: (b) CCl₄
Solution:

It is neither an acid nor a base. It is a non-flammable, colorless liquid with a "sweet" chloroform-like smell that can be detected at low levels. Acids - Sour to taste, turn the blue litmus red, do not change the color of red litmus, do not change the color of turmeric indicator. Bases - Bitter to taste, do not change the color of blue litmus, turn the red litmus blue, turn the color of turmeric indicator to red.

4. A solution turns blue litmus to red, its pH is likely to be______. [RRB Group D 28/09/2018 (Morning)]

Correct Answer: (c) 6
Solution:

Base turns red litmus blue and acid turns blue litmus red. Acidic substances change the color of the solution from purple to red or pink. Neutral substances turn the purple solution to blue. Basic substances change the color of the purple solution to green or yellow. Some pH value: Seawater (8.1), human body (7.4), vinegar (2.4).

5. The element common to all acids is : [RRB Group D 28/09/2018 (Evening)]

Correct Answer: (b) Hydrogen
Solution:

All the acids contain hydrogen which dissolves in water to produce hydrogen ions. A solution with pH value less than 7 is acidic and more than 7 is basic. A pH of 7 means that the number of hydrogen ions and hydroxide ions in a solution are equal.

6. Which of the following is not correct regarding alkali? [RRB Group D 01/10/2018 (Afternoon)]

Correct Answer: (d) Turns blue litmus red
Solution:

Litmus is a Natural indicator to test acid and bases. It is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.

7. The substances whose odour changes in acidic or basic media are called_____. [RRB Group D 01/10/2018 (Evening)]

Correct Answer: (d) Olfactory indicators
Solution:

Such substances can be used in the laboratory to test whether a solution is a base or an acid, and this process is called olfactory titration. Examples - onion, clove oil and vanilla extract. Natural indicators - A class of indicators that are present in nature that may tell if a compound is basic or acidic.
Synthetic indicators - Indicators that are synthesized in the laboratory and they indicate the presence of acid or base by changing their colour. Acid-base indicators - Compounds that change color at a particular pH.

8. Which of the following statements is/are true/false? [RRB Group D 01/10/2018 (Evening)]

A. An acid which is completely ionized into ions and produces a large number of H⁺ ions. For example HCl, H₂SO₄, HNO₃
B. An acid which is partially ionized in water and produces less number of H⁻  ions. Form example CH₃COOH, H₂CO₃ , H₂SO₃ ,

Correct Answer: (a) Both A and B are true
Solution:

Acids : The compounds which produce hydrogen (H⁺) ions when dissolved in water. Chemical properties of acids : Acids react with metals to form salts and release hydrogen gas, Acids react with bases to form salts and water, which is also known as a neutralization reaction, Acids have a pH value of less than 7.

9. What is the natural source of Oxalic acid? [RRB Group D 03/10/2018 (Morning)]

Correct Answer: (a) Tomato
Solution:

It is a dicarboxylic acid and naturally occurring organic acid in plants, vegetables, etc. Natural Source and their Acid: Vinegar (Acetic acid), Orange (Citric), Tamarind, Grapes (Tartaric), Sour milk, Curd (Lactic), Lemon (Citric), Ant sting (Methanoic acid), Apple (Malic).

10. Which one of the following is highly exothermic? [RRB Group D 03/10/2018 (Afternoon)]

Correct Answer: (d) Dissolving sulphuric acid in water
Solution:

Sulfuric acid (H₂SO₄) is a strong mineral acid and soluble in water at all concentrations. If water is mixed to concentrate sulphuric acid, it acts to boil and spits. Exothermic - reaction in which energy is released in the form of light or heat. Endothermic - reactions in which the reactants absorb heat energy from the surroundings.