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.

Short answer

Statement (b) about water is false.

Step-by-step solution

Understanding the Properties of Water

Let's first identify true properties of water. Water acts as both an acid (proton donor) and a base (proton acceptor), which is known as being amphoteric. Hence, statement (a) is true.

Analyzing Hydrogen Bonding

Next, consider the nature of hydrogen bonding in water. Water exhibits extensive intermolecular, not intramolecular, hydrogen bonding due to interactions between different water molecules. Therefore, statement (b) is false.

Considering Ice Formed by Heavy Water

Ice formed by heavy water (D2O) is denser than normal water and will sink in it. Thus, statement (c) is true.

Photosynthesis Reaction

In photosynthesis, water is oxidized to form oxygen gas (O_2). This makes statement (d) true.

Key concepts

Amphoterism

Water has the unique ability to act both as an acid and a base. This behavior is known as amphoterism. When water acts as an acid, it donates a proton (\(H^+\)), and when it acts as a base, it accepts a proton.
The chemical reaction that showcases this property is the self-ionization of water:\[2H_2O(l) \rightleftharpoons H_3O^+(aq) + OH^-(aq)\]This reaction demonstrates how one molecule of water donates a hydrogen ion to another, functioning as an acid, while the receiving molecule acts as a base.
Amphoterism is significant because it allows water to neutralize both acids and bases. This property is pivotal in many chemical reactions, making water a universal solvent crucial for life.

Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole attraction between water molecules. It's not to be confused with typical covalent bonds.
In water, hydrogen bonds form between the hydrogen atom of one water molecule and the oxygen atom of another. This intermolecular bonding is responsible for many of water’s unique properties, such as high surface tension, high boiling point, and its role in temperature regulation in living systems.
Contrary to what's sometimes assumed, water does not have intramolecular hydrogen bonding – meaning these bonds do not occur within a single water molecule but rather between multiple water molecules.

• Hydrogen bonds are relatively weak compared to covalent bonds but are strong enough to affect the physical properties of compounds.
• They are essential for the structure and function of biological molecules like proteins and nucleic acids.

Photosynthesis

Photosynthesis is the process through which plants, algae, and certain bacteria convert light energy into chemical energy, storing it in the bonds of glucose. Water plays a critical role in this process.
During photosynthesis, water is split in a reaction known as photolysis. This reaction produces oxygen gas (\(O_2\)), protons, and electrons, which are then used in different phases of the photosynthetic process.
The general equation for photosynthesis is:\[6CO_2 + 6H_2O + light \rightarrow C_6H_{12}O_6 + 6O_2\]This equation shows how water is oxidized to release oxygen as a by-product. Through this vital process, plants provide oxygen, which is essential for all aerobic organisms, including humans.

• The oxygen produced helps maintain the atmospheric balance necessary for life.
• Understanding photosynthesis is crucial for fields such as agriculture and environmental science.

Heavy Water Ice Density

Heavy water, or deuterium oxide (\(D_2O\)), is similar to regular water but with deuterium atoms instead of hydrogen. These atoms increase the molecular weight, affecting its density.
When heavy water freezes to form ice, its density is greater than that of regular water. As a result, ice made from heavy water sinks in normal water. This is different from regular ice, which floats due to its lower density compared to liquid water.
Understanding this property has implications in scientific research and nuclear reactors, where heavy water is used as a neutron moderator.

• Since heavy water ice sinks, it provides a different study model for scientists compared to standard water ice.
• It also serves as a tool in certain types of industrial and medical applications due to its unique properties.