1. ____________ is one of the few ____________ found in a ____________ state over most of ____________ surface.
2. where are most of the shared electrons found in water molecules? ______________________
3. what does it mean when a molecule is said to be polar?
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4. define hydrogen bond:
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5. how does the structure of water contribute to its unique properties?
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6. define cohesion:
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7. define adhesion:
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8. how are cohesion and adhesion similar? how are they different?
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9. why is water’s heat capacity relatively high? _______________________________________
10. the human body’s mass is composed of about ____________ water.
11. define mixture:
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____________________________________________________________________________________
12. define solution:
____________________________________________________________________________________
13. define solute:
____________________________________________________________________________________
14. define solvent:
____________________________________________________________________________________

Question

Accepted Answer

### Question 1
# Brief Explanations:
Water is one of the few substances found in a liquid state over most of Earth’s surface. This is because of water's unique molecular structure and intermolecular forces (like hydrogen bonding) that allow it to remain liquid in a wide range of temperatures common on Earth.
# Answer:
Water; substances; liquid; Earth’s

### Question 2
# Brief Explanations:
In a water molecule ($H_2O$), oxygen is more electronegative than hydrogen. Electronegativity refers to an atom's ability to attract shared electrons in a covalent bond. So, the shared electrons in the covalent bonds between oxygen and hydrogen are pulled more towards the oxygen atom. Thus, most of the shared electrons are found closer to the oxygen atom in water molecules.
# Answer:
Most of the shared electrons in water molecules are found closer to the oxygen atom (because oxygen is more electronegative than hydrogen and pulls the shared electrons more strongly towards itself).

### Question 3
# Brief Explanations:
A polar molecule has a distribution of electrical charge such that one end (or region) of the molecule is slightly positive and the other end (or region) is slightly negative. This occurs due to an unequal sharing of electrons in the molecule's covalent bonds (usually because of differences in electronegativity between the atoms involved) and an asymmetrical molecular shape, which results in a permanent dipole moment (a separation of positive and negative charges within the molecule). For example, in water ($H_2O$), the oxygen end is slightly negative and the hydrogen ends are slightly positive.
# Answer:
A polar molecule is one in which there is an unequal distribution of electrical charge, resulting in a molecule with a slightly positive region and a slightly negative region (due to unequal electron sharing and molecular geometry).

### Question 4
# Brief Explanations:
A hydrogen bond is a weak intermolecular force that occurs when a hydrogen atom, which is covalently bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) in one molecule, is attracted to another highly electronegative atom (in a different molecule or sometimes within the same molecule). The highly electronegative atom pulls the electron from the hydrogen, making the hydrogen have a partial positive charge, which then is attracted to the partial negative charge of the electronegative atom in another molecule. For example, in water, the hydrogen of one water molecule is hydrogen - bonded to the oxygen of another water molecule.
# Answer:
A hydrogen bond is a weak intermolecular force where a hydrogen atom (covalently bonded to a highly electronegative atom like O, N, or F) is attracted to a highly electronegative atom in another (or the same) molecule.

### Question 5
# Brief Explanations:
1. **Polarity and Hydrogen Bonding**: Water has a bent molecular shape with two hydrogen atoms bonded to an oxygen atom. Oxygen is more electronegative than hydrogen, so the electrons in the O - H bonds are pulled towards oxygen, making the oxygen end slightly negative and the hydrogen ends slightly positive. This polarity allows water molecules to form hydrogen bonds with each other.
2. **Effect on Properties**:
   - **Cohesion and Surface Tension**: The hydrogen bonds between water molecules lead to cohesion (attraction between water molecules). This cohesion, along with surface tension (a result of cohesive forces at the surface), allows water to form droplets and support small organisms on its surface.
   - **Adhesion**: Water molecules also form hydrogen bonds with other polar or charged substances, leading to adhesion (attraction between water and other substances). This is seen in capillary action, where water can move up narrow tubes (like xylem in plants) against gravity.
   - **High Specific Heat Capacity**: To break the hydrogen bonds, a relatively large amount of heat energy is required. So, water can absorb or release a lot of heat with only a small change in temperature, which helps regulate temperatures in organisms and the environment.
   - **Expansion upon Freezing**: When water freezes, the hydrogen bonds form a regular, open - lattice structure, causing ice to be less dense than liquid water. This is why ice floats, which is important for aquatic ecosystems as it insulates the water below.
   - **Universal Solvent**: The polar nature of water allows it to surround and dissolve many ionic and polar substances. The positive part of the water molecule (hydrogen) is attracted to negative ions, and the negative part (oxygen) is attracted to positive ions, pulling the solute particles apart.
# Answer:
Water’s structure (polar, bent shape, hydrogen - bonding ability) leads to unique properties: polarity and H - bonding cause cohesion (surface tension), adhesion (capillary action), high heat capacity (temperature regulation), expansion on freezing (ice floats), and water being a universal solvent (dissolves polar/ionic substances).

### Question 6
# Brief Explanations:
Cohesion is the attraction between molecules of the same substance. In the case of water, cohesion occurs due to the hydrogen bonds between water molecules. For example, when water forms droplets, it is because the water molecules are more attracted to each other (due to cohesion) than to the surrounding air.
# Answer:
Cohesion is the attraction between molecules of the same substance (e.g., water molecules attracting other water molecules, due to hydrogen bonding in water).

### Question 7
# Brief Explanations:
Adhesion is the attraction between molecules of different substances. For water, adhesion occurs when water molecules are attracted to molecules of other polar or charged substances. For example, when water wets a glass surface, the water molecules are attracted to the polar molecules in the glass (like silicate groups), showing adhesion.
# Answer:
Adhesion is the attraction between molecules of different substances (e.g., water molecules attracting to glass or other polar/charged substances).

### Question 8
# Brief Explanations:
- **Similarities**: Both cohesion and adhesion are intermolecular forces that involve the attraction between molecules. They are both important in determining the behavior of substances, especially in the case of water, and are related to the polarity of molecules (in the case of water, hydrogen bonding plays a role in both).
- **Differences**: Cohesion is the attraction between molecules of the same substance (e.g., water - water attraction), while adhesion is the attraction between molecules of different substances (e.g., water - glass attraction). In terms of effects, cohesion leads to phenomena like surface tension and water droplets, while adhesion leads to phenomena like capillary action and wetting of surfaces.
# Answer:
- **Similarities**: Both are intermolecular attractive forces.
- **Differences**: Cohesion is between same - substance molecules (e.g., water - water); adhesion is between different - substance molecules (e.g., water - glass).

### Question 9
# Brief Explanations:
Water has a relatively high heat capacity because of the hydrogen bonds between its molecules. When heat is added to water, a significant amount of the heat energy is used to break the hydrogen bonds between the water molecules rather than just increasing the kinetic energy of the molecules (which would raise the temperature). Conversely, when heat is removed, the formation of hydrogen bonds releases energy, helping to keep the temperature from dropping too quickly. So, a large amount of heat must be added or removed to change the temperature of water, resulting in a high heat capacity.
# Answer:
Water’s high heat capacity is due to hydrogen bonds: much heat energy is used to break H - bonds (rather than just increasing molecular kinetic energy/temperature), so a large heat change is needed for a small temperature change.

### Question 10
# Brief Explanations:
The human body's mass is composed of about 60 - 70% water (the average is often stated as around 60% - 65% for adults, though it can vary with factors like age, gender, and body composition). This water is essential for various physiological processes like transporting nutrients, regulating temperature, and facilitating chemical reactions.
# Answer:
60 - 70% (or approximately 60% - 65% for adults, with variation based on factors like age, gender, and body composition)

### Question 11
# Brief Explanations:
A mixture is a combination of two or more substances in which each substance retains its own chemical properties. The substances in a mixture are not chemically combined (unlike in a compound) and can be present in varying proportions. Mixtures can be homogeneous (where the components are evenly distributed, like a salt - water solution) or heterogeneous (where the components are not evenly distributed, like a mixture of sand and water).
# Answer:
A mixture is a combination of two or more substances where each substance retains its chemical properties (substances are not chemically combined and can be in variable proportions; can be homogeneous or heterogeneous).

### Question 12
# Brief Explanations:
A solution is a homogeneous mixture composed of a solute and a solvent. The solute is the substance that is dissolved, and the solvent is the substance in which the solute is dissolved. In a solution, the solute particles are evenly distributed throughout the solvent at the molecular or ionic level. For example, in a salt - water solution, salt is the solute and water is the solvent, and the salt ions are evenly distributed in the water.
# Answer:
A solution is a homogeneous mixture of a solute (dissolved substance) and a solvent (substance doing the dissolving), with solute particles evenly distributed at the molecular/ionic level.

### Question 13
# Brief Explanations:
A solute is the substance that is dissolved in a solvent to form a solution. The solute can be a solid, liquid, or gas. For example, in a sugar - water solution, sugar is the solute; in an alcohol - water solution (where alcohol is the solute and water is the solvent), alcohol is the solute. The solute particles are dispersed within the solvent.
# Answer:
A solute is the substance that is dissolved in a solvent to form a solution (can be solid, liquid, or gas, dispersed in the solvent).

### Question 14
# Brief Explanations:
A solvent is the substance that dissolves a solute to form a solution. The solvent is usually the component present in the greater amount (though not always, in some cases like alloys, the concept is a bit different but in typical liquid - based solutions, this holds). Water is a common solvent (called the universal solvent) as it can dissolve many ionic and polar substances. Other examples include alcohol (used to dissolve substances like iodine) and acetone (used to dissolve nail polish).
# Answer:
A solvent is the substance that dissolves a solute to form a solution (usually present in greater amount, e.g., water, alcohol, acetone).

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