Q: A biologist wants to prepare 500 mL of a 0.2 M NaCl solution. The molar mass of NaCl is 58.44 g/mol. How many grams of NaCl are needed?

$$0.2 \times 0.5 \times 58.44 = 5.844 g$$

Question 1

Which property of water is primarily responsible for the ability of some insects to walk on the surface of a pond without sinking?

Accepted Answer

Surface tension due to cohesion

Question 2

A scientist dissolves table salt (NaCl) in water. What is the best explanation for why NaCl dissolves so readily in water?

Accepted Answer

Water molecules surround Na+ and Cl- ions due to their polarity, forming hydration shells

Question 3

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

Accepted Answer

Hydrogen bonds in ice are more ordered, making ice less dense than liquid water

Question 4

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

Accepted Answer

$$5$$

Question 5

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

Accepted Answer

Sweat evaporates from human skin, removing heat and cooling the body

Question 6

A biologist wants to prepare 500 mL of a 0.2 M NaCl solution. The molar mass of NaCl is 58.44 g/mol. How many grams of NaCl are needed?

Accepted Answer

$$0.2 	imes 0.5 	imes 58.44 = 5.844 g$$

Question 7

Which of the following statements about acids and bases is correct?

Accepted Answer

An acid increases the concentration of H+ ions in a solution

Question 8

If the pH of a solution changes from 6 to 4, what happens to the concentration of hydrogen ions ($$[H^+]$$)?

Accepted Answer

It increases by 100-fold

Question 9

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

Accepted Answer

Hydrogen bonds between water molecules require a lot of energy to break

Question 10

A marine biologist is studying the effects of ocean acidification. Which chemical reaction best represents the process by which increased atmospheric $$CO_2$$ leads to lower ocean pH?

Accepted Answer

$$CO_2 + H_2O$$ \rightarrow H_2CO_3 \rightarrow H^+ + $$HCO_3$$^-$$

Question 11

Which of the following best describes a hydrophobic substance?

Accepted Answer

It is composed mostly of non-polar bonds and repels water

Question 12

A buffer solution is important in biological systems because it:

Accepted Answer

Minimizes changes in concentrations of $$H^+$$ and $$OH^-$$ ions

Question 13

Which of the following is NOT one of the four emergent properties of water that facilitate life?

Accepted Answer

High density as a solid

Question 14

A student adds 1 mole of glucose (molar mass = 180 g/mol) to enough water to make 2 liters of solution. What is the molarity of the solution?

Accepted Answer

$$0.5 M$$

Question 15

Which of the following best explains why coastal cities tend to have milder climates than inland cities at the same latitude?

Accepted Answer

Water has a high specific heat, moderating temperature fluctuations

Question 16

Which of the following is a correct conversion between calories and joules?

Accepted Answer

$$1$$ cal $$= 4.184 J$$

Question 17

Which of the following best describes the difference between cohesion and adhesion?

Accepted Answer

Cohesion is the attraction between like substances; adhesion is the attraction between different substances

Question 18

A solution has a pH of 8. Which of the following statements is true?

Accepted Answer

The solution is basic

Question 19

Which of the following best explains why water is an effective solvent for ionic and polar substances?

Accepted Answer

Water's polarity allows it to surround and separate charged and polar molecules

Question 20

If all ice sank instead of floating, which of the following would most likely occur on Earth?

Accepted Answer

Bodies of water would freeze from the bottom up, threatening aquatic life

Chapter 3: Water & Life – Properties and Importance of Water in Biology

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