Problem 145 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statement about water is false? (a) Water can act both as an acid and as a base. (b) There is a extensive intramolecular hydrogen bonding in the condensed phase. (c) Ice formed by heavy water sinks in normal water (d) Water in oxidised to \(\mathrm{O}_{2}\) daring photosynthesis.

Step-by-Step Solution

Answer

Statement (b) is false.

Step 1: Understanding the Question

We need to determine which statement about water is not true. The statements pertain to the chemical and physical properties of water.

Step 2: Evaluating Statement (a)

Statement (a) suggests that water can act both as an acid and as a base. This is known as amphoteric behavior. Water can donate a proton to become a hydroxide ion ( ext{OH}⁻) or accept a proton to become a hydronium ion ( ext{H}_3 ext{O}⁺). Therefore, statement (a) is true.

Step 3: Evaluating Statement (b)

Statement (b) claims that there is extensive intramolecular hydrogen bonding in the condensed phase of water. Hydrogen bonding in water is primarily intermolecular, involving attractions between molecules rather than within a single molecule. Thus, statement (b) is false.

Step 4: Evaluating Statement (c)

Statement (c) suggests that ice formed by heavy water sinks in normal water. Ice formed from heavy water ( ext{D}_2 ext{O}) is denser than normal water and will sink. Therefore, statement (c) is true.

Step 5: Evaluating Statement (d)

Statement (d) states that water is oxidized to ext{O}_2 during photosynthesis. This is true as water is split in the light-dependent reactions of photosynthesis to release oxygen. Therefore, statement (d) is true.

Key Concepts

Amphoteric Behavior

Water is quite a unique substance due to its ability to act both as an acid and a base, a property known as amphoteric behavior. This remarkable capability is evident in water's participation in acid-base reactions. When water acts as an acid, it donates a proton ( +), converting into a hydroxide ion ( {OH}^-). Conversely, when water acts as a base, it accepts a proton to form a hydronium ion ( {H_3O}^+).

Such behavior is fundamental in many biological and chemical processes. For instance, this enables water to maintain a balanced pH in biological systems and supports chemical equilibrium in various reactions. It's important to note that this ability is not very common among substances, making water's amphoteric nature a special characteristic.

• This dual ability of water to either donate or accept protons showcases its versatility.
• Amphoteric behavior helps regulate key processes in both living organisms and the environment.

Intermolecular Hydrogen Bonding

A key property that makes water a rather intriguing compound is its ability to form strong hydrogen bonds between molecules, known as intermolecular hydrogen bonding. Unlike intramolecular hydrogen bonding, which involves bonding within the same molecule, intermolecular bonds occur between different molecules. These bonds are responsible for many of water's unique properties.

For example, hydrogen bonds contribute to water's high boiling and melting points compared to other molecules of similar size. These bonds also lead to a high surface tension, making water droplets form beads on surfaces.

• Hydrogen bonds hold water molecules closely together, resulting in a liquid state under normal conditions.
• These bonds impact water's specific heat capacity, enabling it to absorb or release significant amounts of heat with little temperature change.

When in solid form, such as ice, these hydrogen bonds arrange water molecules in a lattice structure that actually takes up more space than the liquid form, hence ice floating on liquid water despite statement (c) focusing on heavy water.

Photosynthesis Oxygen Production

Water plays a crucial role in photosynthesis, the process by which plants produce oxygen and food energy. During the light-dependent reactions of photosynthesis, water molecules are split, a process known as photolysis. This splitting releases oxygen gas ( {O}_2), a vital byproduct for life on Earth.

The overall reaction transforms water and carbon dioxide into glucose and oxygen, providing fuel for the plant and oxygen for the environment. This process also illustrates the role of water as a reactant that is essential in sustaining plant life and indirectly supporting the survival of aerobic organisms.

• Oxygen released from photosynthesis originates from the water molecules absorbed by plants.
• This process highlights the essential nature of water in ecological and atmospheric balance.

Water’s involvement in photosynthesis thus underscores its critical importance in global life-support processes, making the exploration of its properties key to understanding ecological dynamics.