Q: A solution has a pH of 4. What is the concentration of hydrogen ions $$[H^+] in $$the solution?

$$[H^+] = 1 \times 10$$^{-4}$$ \text{ M}$$

Question 1

Which of the following best distinguishes an element from a compound?

Accepted Answer

An element is a substance that consists of only one type of atom and cannot be broken down further by chemical reactions, while a compound is made up of two or more elements chemically combined.

Question 2

Which of the following elements is NOT among the top six that make up 96% of living matter?

Accepted Answer

Calcium

Question 3

Given an atom with atomic number 8 and mass number 18, how many neutrons does it have?

Accepted Answer

$$18 - 8 = 10$$ neutrons

Question 4

Radioactive isotopes are important to biologists because:

Accepted Answer

They can be used as tracers to follow atoms through metabolic processes.

Question 5

Which type of chemical bond involves the sharing of electron pairs between atoms?

Accepted Answer

Covalent bond

Question 6

Why are weak chemical bonds, such as hydrogen bonds, important in living organisms?

Accepted Answer

They allow molecules to interact temporarily, which is essential for processes like enzyme activity and DNA replication.

Question 7

A water molecule has a bent shape due to:

Accepted Answer

The presence of two lone pairs of electrons on the oxygen atom.

Question 8

Which property of water allows it to moderate Earth's temperature?

Accepted Answer

High specific heat

Question 9

Water's ability to dissolve many substances is due to its:

Accepted Answer

Polarity, which allows it to surround and separate ions and polar molecules

Question 10

Which equation represents the dissociation of water?

Accepted Answer

$$2H_2O \rightarrow H_3O^+ + OH^-$$

Question 11

A solution has a pH of 4. What is the concentration of hydrogen ions $$[H^+] in $$the solution?

Accepted Answer

$$[H^+] = 1 	imes 10$$^{-4}$$ 	ext{ M}$$

Question 12

Which of the following best explains why ice floats on liquid water?

Accepted Answer

Hydrogen bonds in ice create a lattice that spaces molecules farther apart, making ice less dense than liquid water.

Question 13

Which property of water is most directly responsible for the movement of water from the roots to the leaves in plants?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding

Question 14

Which statement best describes a hydrophilic substance?

Accepted Answer

It has polar regions that can form hydrogen bonds with water.

Question 15

How does the polarity of water molecules make water a versatile solvent?

Accepted Answer

It allows water to form hydrogen bonds with polar molecules and ions, surrounding and separating them.

Question 16

Which of the following is a real-world example of how water's high heat of vaporization benefits living organisms?

Accepted Answer

It enables sweating to cool the body by releasing heat as water evaporates from the skin.

Question 17

A scientist adds NaOH to a solution, increasing the concentration of $$OH^-$$ ions. What effect does this have on the $$[H^+]$$ concentration?

Accepted Answer

It decreases $$[H^+] by $$combining $$OH^-$$ with $$H^+ to $$form water.

Question 18

Which of the following best explains why the shape of a molecule influences its biological function? Use hemoglobin as an example.

Accepted Answer

The shape determines how molecules interact with other molecules, such as hemoglobin's ability to carry oxygen due to its specific structure.

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