Q: If the concentration of $$[H^+] in a $$solution is $$1 \times 10$$^{-9}$$ M, what is the concentration of $$[OH^-]$$ at 25$$^\circ$$C, given that $$[H^+][OH^-] = 1 \times $$10^{-14}$$?

$$[OH^-] = 1 \times 10$$^{-5}$$ M

Question 1

Which property of water is primarily responsible for the fact that ice floats on liquid water, and why is this property biologically significant?

Accepted Answer

Water's expansion upon freezing; ice is less dense than liquid water, preventing bodies of water from freezing solid and allowing aquatic life to survive beneath the ice.

Question 2

A scientist is studying a solution with a hydrogen ion concentration of $$1 	imes 10$$^{-5}$$ M. What is the pH of this solution?

Accepted Answer

$$pH = 5$$

Question 3

Which of the following best explains why water has a high specific heat compared to other substances?

Accepted Answer

Hydrogen bonds between water molecules absorb heat when they break and release heat when they form, requiring more energy to change temperature.

Question 4

A marine biologist observes that coral reefs are declining in areas with increased atmospheric $$CO_2. $$Which chemical process best explains this phenomenon?

Accepted Answer

Increased $$CO_2$$ leads to more carbonic acid in seawater, which increases $$H^+$$ concentration and reduces carbonate ions needed for calcification.

Question 5

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

Accepted Answer

A buffer is a weak acid and its corresponding base that minimizes changes in pH by accepting or donating $$H^+$$ ions.

Question 6

If the concentration of $$[H^+] in a $$solution is $$1 	imes 10$$^{-9}$$ M, what is the concentration of $$[OH^-]$$ at 25$$^\circ$$C, given that $$[H^+][OH^-] = 1 	imes $$10^{-14}$$?

Accepted Answer

$$[OH^-] = 1 	imes 10$$^{-5}$$ M

Question 7

Why is water considered a 'universal solvent' in biological systems?

Accepted Answer

Water's polarity allows it to form hydrogen bonds with charged and polar molecules, dissolving a wide variety of substances.

Question 8

A solution is made by dissolving 2 moles of NaCl in enough water to make 1 liter of solution. What is the molarity ($$M) of $$NaCl in this solution?

Accepted Answer

$$2\ M$$

Question 9

Which of the following scenarios best illustrates the concept of evaporative cooling?

Accepted Answer

A dog pants to cool down after running, as water evaporates from its tongue, removing heat from its body.

Question 10

Which of the following best explains why coastal regions tend to have milder climates than inland regions?

Accepted Answer

Water's high specific heat allows it to absorb and release large amounts of heat, moderating temperature changes.

Question 11

A patient’s blood pH drops from 7.4 to 7.1. Which buffer system in the blood helps restore pH, and how does it respond?

Accepted Answer

The carbonic acid-bicarbonate buffer system; bicarbonate ($$HCO_3$$^-$$) accepts excess H$$^+$$ ions to raise pH.

Question 12

Which of the following substances is most likely to be hydrophobic?

Accepted Answer

A molecule dominated by nonpolar covalent bonds, such as oil.

Question 13

If a solution has a pH of 3, how does its $$[H^+]$$ compare to a solution with a pH of 6?

Accepted Answer

It has 1,000 times higher $$[H^+]$$ concentration.

Question 14

Which of the following best describes the process of hydration shells forming around ions in solution?

Accepted Answer

Water molecules surround ions, with the partially negative oxygen facing cations and the partially positive hydrogens facing anions.

Question 15

A student adds hydrochloric acid ($$HCl) to $$pure water. What happens to the $$[H^+]$$ and $$[OH^-]$$ concentrations?

Accepted Answer

$$[H^+]$$ increases and $$[OH^-]$$ decreases.

Question 16

Which of the following is a real-world consequence of ocean acidification caused by increased atmospheric $$CO_2$$?

Accepted Answer

Reduced availability of carbonate ions for marine organisms to build calcium carbonate shells.

Question 17

Which equation correctly represents the relationship between pH and hydrogen ion concentration?

Accepted Answer

$$pH = -\log [H^+]$$

Question 18

Why is the abundance of water critical for the habitability of Earth?

Accepted Answer

Water's unique properties support life by moderating temperature, acting as a solvent, and enabling chemical reactions necessary for living organisms.

Water: Physical Properties and Biological Importance

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