To identify a weak acid, we need to understand the definition of strong and weak acids. Strong acids dissociate completely in water, while weak acids dissociate only partially.
B) Acetic acid (\(\text{CH}_3\text{COOH}\)): Acetic acid is a carboxylic acid. When dissolved in water, it undergoes partial dissociation, establishing an equilibrium:
\[ \text{CH}_3\text{COOH} \text{(aq)} + \text{H}_2\text{O} \text{(l)} ightleftharpoons \text{CH}_3\text{COO}^- \text{(aq)} + \text{H}_3\text{O}^+ \text{(aq)} \]Because it only partially dissociates, it is classified as a weak acid.
The question asks for the best description of a strong base. To answer this, we need to recall the definition of strong bases in chemistry, particularly how they behave in aqueous solutions.
D) Ionises almost completely in aqueous solution
This statement directly aligns with the chemical definition of a strong base. For example, sodium hydroxide (\(\text{NaOH}\)) is a strong base because it dissociates almost entirely into \(\text{Na}^+\) and \(\text{OH}^-\) ions when dissolved in water:
\[ \text{NaOH (aq)} \rightarrow \text{Na}^+\text{(aq)} + \text{OH}^-\text{(aq)} \]
This complete ionisation is the defining characteristic of a strong base.
The question asks for the definition of 'Glacial acetic acid'. This term refers to a specific form of acetic acid, and understanding its properties is key to identifying the correct option.
A) Pure (water-free) acetic acid, which can solidify into ice-like flakes in cold climate. This is the precise definition of glacial acetic acid, owing to its high freezing point and ice-like appearance when solid.
The dilution of concentrated acids is a highly exothermic process, meaning it releases a significant amount of heat. To ensure safety and prevent dangerous reactions like boiling, splashing, or even container breakage, a specific procedure must be followed. The key is to manage the heat generated during the mixing process.
Correct Option: B) Add the concentrated acid slowly to water, with constant stirring
This method ensures that the large volume of water can absorb the heat generated during the exothermic dilution process, preventing dangerous boiling and splashing. Adding the acid slowly and stirring constantly helps to dissipate the heat evenly and control the reaction.
The question asks to identify a natural substance that acts as an indicator, showing a specific color change in acidic and basic mediums. We need to recall the properties of common acid-base indicators, especially natural ones.
C) Turmeric is a natural indicator that is yellow in acidic solutions and turns reddish-brown in basic solutions. This property is often observed in daily life, for instance, when curry (containing turmeric) stains a white cloth and then turns reddish-brown when washed with soap (which is basic).
The question asks about the color changes of phenolphthalein, a common synthetic indicator, in acidic and basic solutions. To answer this, one needs to recall the characteristic color properties of phenolphthalein across different pH ranges.
C) Colourless in an acidic solution and pink in a basic solution. This statement accurately describes the color changes of phenolphthalein in acidic and basic media.