Properties of Water (AS)

What is the shape of water?

• Linear

• Tetrahedral

• Bent

• Trigonal planar

Answer explanation

The question asks about the geometrical shape of water. The correct answer is 'Bent'. In a water molecule, the oxygen atom shares each of its two lone pairs of electrons with two hydrogen atoms. This forms a bent molecular geometry (or V-shaped). The bond angle is approximately 104.5 degrees, less than the 109.5 degrees for a perfect tetrahedron, due to the effects of electron-electron repulsion.

What is the charge of oxygen in a water molecule?

• Positive

• Negative

• Neutral

• Variable

Answer explanation

Within a water molecule, oxygen has a charge of negative. This is due to the oxygen atom's ability to pull electrons towards itself more strongly than the hydrogen atoms, resulting in a partial negative charge. Therefore, the correct answer is 'Negative'.

What type of bonds form between water molecules?

• Covalent bonds

• Ionic bonds

• Hydrogen bonds

• Van der Waals forces

Answer explanation

Water molecules form hydrogen bonds with each other. This happens because water is a polar molecule, with the oxygen (O) atom being more negatively charged than the hydrogen (H) atoms. This difference in charge causes the negative oxygen atom in one molecule to be attracted to the positive hydrogen atom in another molecule, forming a hydrogen bond.

What property of water allows it to stick to the xylem walls in plants?

• Adhesion

• Cohesion

• Surface tension

• Solvent power

Answer explanation

The property of water that allows it to stick to the xylem walls in plants is called adhesion. This is a property of water that refers to its ability to stick to other substances, not just to itself. It's this characteristic that enables water to travel upward against gravity in plants, a critical aspect of their survival and growth.

What is the reason behind the surface tension of water?

• Cohesion

• Adhesion

• Specific heat

• Evaporation

Answer explanation

The surface tension of water is due to Cohesion. Cohesion refers to the attraction between molecules of the same substance. In the case of water, its molecules are strongly attracted to each other, creating a sort of 'skin' on its surface - this is surface tension.

What type of molecules can water dissolve?

• Nonpolar molecules

• Hydrophobic molecules

• Polar molecules

• Ionic compounds

Answer explanation

Water can dissolve polar molecules because of its own polarity. The positive and negative ends of water molecules attract and mix with the polar molecules, causing them to dissolve. Nonpolar molecules and hydrophobic molecules do not mix or dissolve in water because they do not have charges for the water molecules to interact with. Ionic compounds can also dissolve in water but are not the answer here because the question specifically mentions 'molecules'.

Why does water expand when it freezes?

• It becomes more dense

• It contracts

• It forms covalent bonds

• It breaks hydrogen bonds

Answer explanation

Water expands when it freezes due to the molecular structure of ice. When water is liquid, the molecules move freely, allowing them to be close together. But when water freezes, the molecules form a crystalline structure, maintaining a fixed distance from each other, causing the volume to increase. This contradicts the claim that it contracts, which is the selected answer in the question.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

What property of water helps in stabilizing aquatic environment temperatures?

• Specific heat

• Surface tension

• Adhesion

• Cohesion

Answer explanation

Water's specific heat, which is the energy needed to change the temperature of 1 gram of substance by 1 degree Celsius, plays a crucial role in stabilizing aquatic environment temperatures. This property allows water to absorb and store heat, thereby preventing large temperature swings and providing a stable environment for aquatic life.

What is the purpose of evaporation in cooling organisms?

• To release heat

• To absorb heat

• To increase density

• To break hydrogen bonds

Answer explanation

Evaporation is a process that involves the conversion of water from a liquid to a gas state, which requires heat. Therefore, when organisms evaporate, they absorb heat from their surroundings, effectively cooling themselves. This explains why the correct answer is 'To absorb heat'. This process plays a vital role in maintaining the organism's body temperature.

Tags

NGSS.MS-PS1-4

What organisms use evaporative cooling to regulate temperature?

• Animals only

• Plants only

• Both animals and plants

• Neither animals nor plants

Answer explanation

Both animals and plants use evaporative cooling to regulate temperature. Animals, such as dogs, evaporate water through panting. Similarly, plants transpire water vapor from their leaves to cool down. Thus, the correct answer is both animals and plants.