What is the nature of the new product which is formed by the action of water on quick lime?
Neutral
Acidic
Amphoteric
Basic
(4)
When quick lime is added to water, it reacts to form slaked lime . Slaked lime or calcium hydroxide is basic in nature because it dissociates into OH? ions when dissolved in aqueous solution.
The pH range most conducive for life of fresh water plants and animals is:
6.5–7.5
2.0–3.5
3.5–5.0
9.0–10.5
(1)
A neutral pH is most conducive for life of fresh water plants and animals and the pH range 6.5–7.5 is almost neutral.
Phenolphthalein turns acids to _______ solution.
colourful
colourless
pink
orange
(2)
Phenolphthalein is used as an indicator in acid–base titrations. For this application, it turns acids to colourless solutions and bases to pink solutions.
Which one of the following is acidic in nature?
Gastric juice
Sodium hydroxide solution
Lime water
Blood plasma
(1)
Gastric juice is acidic in nature due to the presence of hydrochloric acid (HCl). This acid is secreted by the stomach lining and plays a crucial role in digestion by providing an acidic environment. In contrast, sodium hydroxide solution (b) is a base, lime water (c) is slightly basic due to the presence of calcium hydroxide, and blood plasma (d) is slightly alkaline with a pH around 7.4, necessary for proper physiological functions.
An aqueous solution ‘A’ turns phenolphthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’, the pink colour disappears. The following statement is true for solution ‘A’ and ‘B’
A is strongly basic and B is a weak base
A is strongly acidic and B is a weak acid.
A has pH greater than 7 and B has pH less than 7
A has pH less than 7 and B has pH greater than 7
(3)
Phenolphthalein solution turns pink in basic solutions. Hence, solution A lies in the pH range of above 7. On adding solution B, the pink colour disappears, hence it has a pH less than 7.
To protect tooth decay we are advised to brush our teeth regularly. The nature of the tooth paste commonly used is:
Acidic
Neutral
Basic
Corrosive
(3)
When we consume acidic food or drinks, the pH of the mouth falls to 5.5 due to which tooth decay occurs. This lowering of pH within the mouth can lead to dental plaque. To protect this, doctors advise to brush the teeth with the toothpaste which are basic in nature as it neutralises the acidic condition inside the mouth. Hence, the nature of the toothpaste should be basic.
Which one of these acid-base indicators is used by a visually impaired student?
Litmus
Turmeric
Vanilla
Phenolphthalein
(3)
Vanilla essence is used as an acid-base indicator because of its smell which helps visually challenged people to realise the change in pH.
When you add a few drops of acetic acid to a test-tube containing sodium bicarbonate powder, which one of the following is your observation?
No reaction takes place
A colourless gas with pungent smell is released with brisk effervescence
A brown coloured gas is released with brisk effervescence
Formation of bubbles of a colourless and odourless gas
(4)
When a few drops of acetic acid is added to the test tube containing sodium bicarbonate powder, sodium acetate is formed along with the release of colourless and odourless CO? gas which can be observed as the bubbles in the test tube.
A student puts a drop of reaction mixture of a saponification reaction first on a blue litmus paper and then on a red litmus paper. He may observe that:
There is no change in the blue litmus paper and the red litmus paper turns white.
There is no change in the red litmus paper and the blue litmus paper turns red.
There is no change in the blue litmus paper and the red litmus paper turns blue.
No change in colour is observed in both the litmus papers.
(3)
Saponification is the alkaline hydrolysis of the fatty acid esters. Hence, the solution is basic, bases with blue litmus gives no colour change. Whereas, on dipping red litmus paper in a mixture of saponification reaction it turns blue
The pH value of a sample of hydrochloric acid is 2. pH value of this sample when diluted by adding water will be:
less than 2 but more than 0
more than 2 but less than 7
more than 7
no change in pH
(2)
When we add water to the solution of hydrochloric acid (pH = 2), the pH will increase till 7 but it will be less than 7 as it contains more hydrogen ions (ions) as compared to hydroxide ions (ions). So, the pH on dilution will be more than 2 but less than 7.
