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

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

Question 1

Which of the following statements best explains why water is considered the 'solvent of life'?

Accepted Answer

Water's polarity enables it to surround and dissolve ionic and polar molecules, forming aqueous solutions.

Question 2

A radioactive isotope of carbon, carbon-14, is used in medical imaging. Which property makes it useful as a tracer in living organisms?

Accepted Answer

It emits radiation that can be detected, allowing scientists to track its movement in biological systems.

Question 3

Which of the following best describes the difference between ionic and covalent bonds?

Accepted Answer

Ionic bonds involve the transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other, while covalent bonds involve the sharing of electrons between atoms.

Question 4

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

Accepted Answer

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

Question 5

Why does ice float on liquid water, and what is the biological significance of this property?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds hold water molecules in a rigid structure, allowing ice to float and insulate bodies of water, protecting aquatic life in winter.

Question 6

Which of the following best explains the process of ocean acidification and its impact on coral reefs?

Accepted Answer

Increased atmospheric $$CO_2$$ dissolves in seawater, forming carbonic acid, which lowers pH and reduces carbonate ion concentration, slowing coral calcification.

Question 7

A molecule of water ($$H_2O) is $$described as a polar molecule. What causes this polarity?

Accepted Answer

The oxygen atom is more electronegative than the hydrogen atoms, pulling shared electrons closer and creating a partial negative charge on oxygen and partial positive charges on hydrogens.

Question 8

Which of the following is an example of a trace element and its biological importance?

Accepted Answer

Fluorine, added to water to help reduce tooth decay.

Question 9

If an atom has an atomic number of 11 and a mass number of 23, how many neutrons does it have?

Accepted Answer

12 neutrons

Question 10

Which property of water allows it to moderate Earth's climate and stabilize temperatures in organisms?

Accepted Answer

Water's high specific heat capacity, due to hydrogen bonding, allows it to absorb and release large amounts of heat with little temperature change.

Question 11

A scientist adds hydrochloric acid ($$HCl) to a $$beaker of pure water, causing the pH to drop from 7 to 2. By what factor has the hydrogen ion concentration increased?

Accepted Answer

By a factor of $$10^5$$

Question 12

Which of the following best describes a buffer and its function in biological systems?

Accepted Answer

A buffer is a substance that minimizes changes in pH by accepting or donating hydrogen ions.

Question 13

Which of the following scenarios demonstrates the concept of cohesion in water?

Accepted Answer

Water molecules stick together, allowing insects to walk on the surface of a pond due to surface tension.

Question 14

Which of the following best explains why sodium chloride ($$NaCl) $$forms from sodium and chlorine atoms?

Accepted Answer

Sodium donates an electron to chlorine, forming oppositely charged ions that attract each other in an ionic bond.

Question 15

A patient is given a solution with a pH of 8. Which of the following best describes this solution?

Accepted Answer

It is basic, with a higher concentration of $$OH^-$$ ions than $$H^+$$ ions.

Question 16

Which of the following is a real-world example of a chemical reaction, and what is the correct representation of the process?

Accepted Answer

The formation of water from hydrogen and oxygen: $$2H_2 + O_2$ \rightarrow 2H_2O$$

Chapter 2: The Chemical Basis of Life – Elements, Atoms, and Compounds

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