【PEP Edition】Junior High Chemistry, Grade 9, Volume 1: Overview of Our Blue Planet's Resources

Looking down from space, Earth is a brilliant blue planet, with about 71% of its surface covered by water. However, hidden beneath this vast expanse of water lies a profound resource paradox:Earth's water reserves are abundant, but the freshwater resources available for use are limited.

1. Global and China's Water Situation

Ocean water storage: Accounts for about 96.5% of the global total water storage. The ocean is a vast resource reservoir, but direct utilization is limited.
Available freshwater: Accounts for about 30.4% of total freshwater, only $1.07 \times 10^{16} \text{ m}^3$.
China's challenge: China's total water resources amount to $2.7 \times 10^{12} \text{ m}^3$, but the per capita water volume is only $2048 \text{ m}^3$, with uneven distribution.

2. Scientific Exploration and Microscopic Nature

Human understanding of water has evolved from macroscopic descriptions to microscopic exploration. Lavoisier once attempted topass steam through a red-hot gun barrelto study its composition, which laid the foundation for establishing water'schemical formula. At the microscopic level, water molecules strictly follow the laws of atomic structure:nuclear charge number = number of protons = number of extranuclear electrons. The atomic nucleus is composed of protons andneutrons. Understanding these rules helps us grasp the composition of substances like $P_2O_5$, $Fe_3O_4$, and understand thatin elementary substances, the oxidation state of an element is 0.

Technology Frontier: Desalination

Through physical purification or chemical pretreatment (such as usingflocculants), we can convert seawater into freshwater. This is a key direction for solving the global water crisis.

QUESTION 1

Which of the following statements about Earth's water resources is correct?

About 71% of Earth's surface is covered by water, so we don't need to conserve water

Ocean water accounts for 96.5% of global water storage and is a valuable source of freshwater

Earth has abundant water reserves, but the freshwater available for use is very limited

The freshwater truly accessible to humans accounts for about 30.4% of total global water storage

QUESTION 2

[Short Answer] Desalination is a way to obtain freshwater from seawater. Can desalination serve as an important approach for humanity to address freshwater shortages, and why?

QUESTION 3

China's per capita water volume is approximately $2048 \text{ m}^3$. If a region's per capita water usage falls below $500 \text{ m}^3$, what is it generally considered to be?

Extreme water scarcity

Mild water scarcity

Adequate water resources

QUESTION 4

[Fill in the blanks] According to the laws of atomic structure, within the hydrogen and oxygen atoms in a water molecule, it always holds that: ____ = number of protons = ____.

QUESTION 5

[Fill in the blanks] Water exists in three states in nature. At 101 kPa, the boiling point of water is ____ $^\circ$C, and its density at $4^\circ$C is ____ $g \cdot cm^{-3}$.