Which one among the following statements with reference to the properties of water is not correct?
Analyzing the Properties of Water
Water is a unique substance with several unusual properties that are essential for life on Earth. Understanding these properties is key to answering questions about its behavior. This question asks us to identify which statement among the given options is not correct regarding the properties of water.
Examining Each Statement on Water Properties
Statement 1: The specific heat of water is abnormally high.
Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius ($1^\circ\text{C}$). Water has a very high specific heat capacity compared to most other liquids and solids. Its specific heat is approximately $4.184 \text{ J/g}^\circ\text{C}$ or $1 \text{ cal/g}^\circ\text{C}$. This high value means that water can absorb a large amount of heat energy without a significant increase in its temperature. This property helps in regulating the temperature of oceans, lakes, and living organisms.
Therefore, this statement is correct.
Statement 2: Latent heat of fusion of water is very low.
Latent heat of fusion ($L_f$) is the amount of heat energy required to change a substance from a solid to a liquid state at its melting point, without changing its temperature. For water, the latent heat of fusion is approximately $334 \text{ J/g}$ or $80 \text{ cal/g}$. This value is relatively high compared to many other substances. A high latent heat of fusion means that a significant amount of energy is needed to melt ice. This property is important in processes like the melting of ice or snow.
Therefore, the statement that the latent heat of fusion of water is very low is not correct. It is, in fact, relatively high.
Statement 3: Density of water is higher than ice.
Density is defined as mass per unit volume. Most substances become denser when they solidify. However, water is an exception. The density of liquid water at $0^\circ\text{C}$ is about $0.9998 \text{ g/cm}^3$, while the density of ice at $0^\circ\text{C}$ is about $0.917 \text{ g/cm}^3$. Since the density of ice is less than the density of liquid water, ice floats on water. This property is crucial for aquatic life in cold climates, as ice forming on the surface insulates the water below.
Therefore, this statement is correct.
Statement 4: Pure water is a non-conductor of electricity.
Electrical conductivity in water is due to the presence of dissolved ions. Pure water, consisting almost exclusively of $\text{H}_2\text{O}$ molecules, undergoes very slight self-ionization, producing very few $\text{H}^+$ and $\text{OH}^-$ ions. Consequently, pure water has very low electrical conductivity, effectively making it a non-conductor or a poor conductor of electricity. The water we encounter daily usually contains dissolved salts and minerals, which provide ions and make it conductive.
Therefore, the statement that pure water is a non-conductor of electricity is essentially correct.
Identifying the Incorrect Statement
Based on the analysis of each statement regarding the properties of water, the statement that is not correct is the one claiming that the latent heat of fusion of water is very low. Water's latent heat of fusion is relatively high.
Revision Table: Key Water Properties Summary
| Property | Description | Water's Behavior/Value | Significance |
|---|---|---|---|
| Specific Heat | Heat required to raise temperature by $1^\circ\text{C}$ | Abnormally High ($\approx 4.184 \text{ J/g}^\circ\text{C}$) | Temperature regulation (climate, bodies) |
| Latent Heat of Fusion | Heat required for solid $\rightarrow$ liquid phase change | Relatively High ($\approx 334 \text{ J/g}$) | Energy needed to melt ice/snow |
| Density (Solid vs. Liquid) | Mass per unit volume | Liquid water is denser than ice | Ice floats, insulating water below |
| Electrical Conductivity | Ability to conduct electric current | Very low for pure water | Conductivity depends on dissolved ions |
Additional Information on Water's Unique Characteristics
Many of water's unusual properties stem from its molecular structure and the strong hydrogen bonds that form between water molecules. These hydrogen bonds require significant energy to break, influencing properties like:
- High Boiling Point and Melting Point: Compared to other molecules of similar size, water has unusually high melting and boiling points.
- High Latent Heat of Vaporization: A large amount of energy is needed to convert liquid water to gas (steam), making sweating an effective cooling mechanism.
- Density Anomaly: The arrangement of water molecules in ice, due to hydrogen bonding, creates a more open structure than in liquid water, making ice less dense.
These unique properties make water indispensable for biological, geological, and climatic processes.
Important Questions from Thermodynamics
A system that does NOT allow exchange of heat with its surrounding is called
A system that does NOT allow exchange of heat with its surrounding is called
- Which of the following statements correctly describes the thermodynamic classification of entropy?
- A mass of $10 \text{ kg}$ is suspended vertically by a rope from the roof. A horizontal force is applied on the rope at a point $P$. The point $P$ is $1 \text{ m}$ vertically below the roof attachment point, and the length of the rope segment from the roof to $P$ is $2 \text{ m}$. If the suspended mass is in equilibrium, what is the tension in the upper part of the rope (from roof to $P$)? (Take $g = 10 \text{ ms}^{-2}$)
Example of thermoplastic among the following is
