Biology SOL Unit 2.1 - Water Chemistry

What is the chemical formula for water?

• H₂O

• H₂O₂

• O₂

• HO₂

Answer explanation

The chemical formula for water is H₂O, indicating it consists of two hydrogen atoms and one oxygen atom. The other options, H₂O₂ (hydrogen peroxide), O₂ (oxygen gas), and HO₂ (hydroperoxyl), are incorrect.

Tags

NGSS.MS-PS1-1

(a)   is the property of water that allows insects to walk on its surface without sinking.

• Adhesion

• Surface tension

• Capillary action

• Dissolution

Answer explanation

Surface tension is the property of water that allows insects to walk on its surface without sinking. It results from the cohesive forces between water molecules, creating a 'skin' effect on the surface.

A​ (a)   mixture is a mixture with a uniform composition throughout, such that one​ (b)   different solute in the mixture, while a​ (c)   mixture is a mixture with uneven composition, such that one​ (d)   the​ different solutes present in the mixture.

• A mixture where you can see all the different parts

• A mixture that cannot dissolve substances

• A mixture that only contains solids

• homogeneus

• heterogeneous

• can see

• cannot see

Answer explanation

A homogeneous mixture has a uniform composition, meaning you cannot see the different parts (cannot see). In contrast, a heterogeneous mixture has an uneven composition, allowing you to see the different parts (can see).

Why is water considered a polar molecule?

• It has equal sharing of electrons between atoms.

• The oxygen atom is slightly negative and the hydrogen atoms are slightly positive.

• It contains only hydrogen atoms.

• It is always in a solid state.

Answer explanation

Water is a polar molecule because the oxygen atom has a slight negative charge, while the hydrogen atoms have slight positive charges. This unequal sharing of electrons creates a dipole moment, making water polar.

How does capillary action help plants?

• It allows water to evaporate quickly

• It helps transport water up plant stems via a transpiration stream

• It prevents water from sticking to leaves

• It increases the boiling point of water

Answer explanation

Capillary action helps plants by allowing water to move upward through the plant stems via a transpiration stream. This process is essential for delivering water and nutrients from the roots to the leaves.

Tags

NGSS.MS-LS2-1

NGSS.MS-LS2-3

What is the main reason water is crucial for the human body?

• It is a source of energy.

• It regulates temperature, carries nutrients, and removes waste.

• It provides structural support.

• It acts as a hormone.

Answer explanation

Water is essential for the human body as it regulates temperature, carries nutrients to cells, and helps remove waste products, making it vital for overall health and proper bodily functions.

Match each organ or body part to the approximate percentage of water it contains.

• Contain about 75% water

• Lungs

• Contain about 73% water

• Brain

• Contain about 83% water

• Bones

• Contain about 22% water

• Heart

Answer explanation

Refer to your notes.

Which statement best explains why water has a high surface tension?

• Water molecules are nonpolar.

• Water molecules have strong cohesion due to polarity.

• Water molecules are loosely bonded.

• Water molecules are always in a gaseous state.

Answer explanation

Water has high surface tension because its molecules are polar, leading to strong cohesive forces. This polarity causes water molecules to attract each other, creating a strong surface layer.

What is the role of a solvent in a mixture?

• It dissolves other substances.

• It is dissolved by other substances.

• It cannot mix with any other substance.

• It forms a solid in the mixture.

Answer explanation

The correct choice is 'It dissolves other substances.' because a solvent is a substance that can dissolve solutes, forming a solution. The other options do not accurately describe the role of a solvent.

Why is water considered a universal solvent?

• It dissolves more substances than any other substance.

• It cannot dissolve any chemicals.

• It only dissolves solids.

• It is always a solute.

Answer explanation

Water is called a universal solvent because it can dissolve more substances than any other liquid, making it essential for various chemical reactions and biological processes.