Question 1

Which property of water is primarily responsible for its ability to dissolve a wide variety of ionic and polar substances?

Accepted Answer

Its high dielectric constant and polarity

Question 2

Refer to the molecular orbital diagram of water. Which molecular orbital is primarily responsible for the lone pair character on the oxygen atom in H$$_2O$$?

Accepted Answer

$$1b_1$$

Question 3

A solution contains 0.154 M NaCl. What is its approximate osmolarity?

Accepted Answer

0.308 Osmol

Question 4

Which of the following best explains why ice is less dense than liquid water?

Accepted Answer

Hydrogen bonds in ice form a rigid, open tetrahedral structure

Question 5

Given the following electronegativities: $$\chi_{O} = 3.5$$, $$\chi_{H} = 2.1$$, what is the percent ionic character of the O-H bond in water?

Accepted Answer

39%

Question 6

Which of the following ions is classified as a kosmotrope and what is its effect on protein solubility?

Accepted Answer

SO$$_4$$^{2-}$$; decreases protein solubility (salting out)

Question 7

Which equation correctly expresses Henry's Law for the solubility of a gas in water?

Accepted Answer

$$c = K_H \cdot p$$

Question 8

A biofilm is growing in an environment with a steep oxygen gradient. Which process is most likely to occur at the bottom of the biofilm?

Accepted Answer

Anaerobic metabolism

Question 9

Which of the following best describes the effect of increasing temperature on the solubility of gases in water?

Accepted Answer

Solubility decreases

Question 10

Which of the following statements about hydrogen bonds in water is correct?

Accepted Answer

Each water molecule can form up to four hydrogen bonds

Question 11

A solution is prepared by dissolving 1 mM Ca$$^{2+} in $$water at pH 6.2 and ionic strength $$I = 5.0 	imes 10$$^{-2}$$. Given a$$_{$$Ca^{2+}$$} = 6.65$$ Å, A = 0.511$, B = 0.33$, calculate the activity of Ca$$^{2+}$$ ions.

Accepted Answer

$$4.9 	imes 10$$^{-4}$$ mol

Question 12

Which of the following best explains the decrease in entropy ($$\Delta S \u003c 0) $$when a nonpolar molecule dissolves in water?

Accepted Answer

Water molecules become more ordered around the nonpolar solute

Question 13

Which of the following is a real-life consequence of the hydrophobic effect?

Accepted Answer

Phase separation of oil and water

Question 14

What is the effect of adding a common ion (e.g., Na$$^+ to a $$saturated AgCl solution) on the solubility of AgCl?

Accepted Answer

Decreases solubility

Question 15

Which of the following best describes the role of compatible solutes (kozmotropi) in microbial cells under osmotic stress?

Accepted Answer

They stabilize macromolecular structures and lower intracellular water activity

Question 16

Which of the following equations correctly relates the osmotic pressure ($$\pi) to $$solute concentration ($$c_B) $$for dilute solutions?

Accepted Answer

$$\pi = c_B R T$$

Question 17

Which of the following is a direct effect of chaotropic ions on proteins?

Accepted Answer

Denaturation and increased solubility of proteins

Question 18

Which of the following best describes the relationship between water activity ($$a_w) $$and microbial growth?

Accepted Answer

Microbial growth is optimal at high $$a_w$$

Question 19

Which of the following is the main reason why glikogen is an efficient energy storage molecule in cells?

Accepted Answer

It is highly branched, allowing storage of large amounts of glucose with minimal increase in osmolarity

Water as the Essential Medium of Life: Structure, Properties, and Biological Relevance

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