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

Question 1

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

Accepted Answer

Ice floats because hydrogen bonds cause water molecules to spread apart when frozen, decreasing its density.

Question 2

A solution has a pH of 5. What is the molar concentration of hydrogen ions ($$[H^+]) in $$this solution?

Accepted Answer

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

Question 3

Which property of water allows it to moderate temperature changes in living organisms?

Accepted Answer

High specific heat and high heat of vaporization

Question 4

What type of chemical bond is formed when two atoms share electrons equally?

Accepted Answer

Nonpolar covalent bond

Question 5

A buffer solution is important in biological systems because it:

Accepted Answer

Maintains a constant pH by accepting or donating $$H^+$$ ions

Question 6

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 7

If a molecule is hydrophobic, what will most likely happen when it is placed in water?

Accepted Answer

It will clump together with other hydrophobic molecules and not dissolve.

Question 8

Which of the following is true about ionic bonds?

Accepted Answer

They are formed by the attraction between oppositely charged ions after electron transfer.

Question 9

Calculate the molecular weight of water ($$H_2O) $$given the atomic masses: $$H = 1$$ and $$O = 16.$$

Accepted Answer

$$18 g/$$mol

Question 10

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound is composed of two or more elements in a fixed ratio, while a mixture is composed of elements and/or compounds in a variable ratio.

Question 11

Which of the following is a consequence of water’s high heat of vaporization for living organisms?

Accepted Answer

It enables evaporative cooling, helping organisms regulate temperature.

Question 12

A solution has a $$[OH^-]$$ concentration of $$1 	imes 10$$^{-9}$$ M. What is its pH?

Accepted Answer

$$pH = 9$$

Question 13

Which of the following is NOT a property of water that is important for life?

Accepted Answer

Water contracts when it freezes

Question 14

What is the atomic number of an element defined as?

Accepted Answer

The number of protons in an atom

Question 15

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak attraction between a hydrogen atom covalently bonded to one atom and attracted to another electronegative atom.

Question 16

Which of the following would most likely increase the acidity of a solution?

Accepted Answer

Adding a substance that increases $$[H^+]$$

Question 17

A molecule with a partial positive charge at one end and a partial negative charge at the other is best described as:

Accepted Answer

Polar

Question 18

Which of the following is the best example of a buffer in biological systems?

Accepted Answer

Bicarbonate buffer

Question 19

If the pH of a solution changes from 7 to 5, how does the concentration of $$H^+$$ ions change?

Accepted Answer

It increases by 100 times.

Question 20

Which of the following best describes the role of electron shells in determining the chemical behavior of an atom?

Accepted Answer

The number of electrons in the outermost shell determines reactivity.

Atoms, Molecules, and Life: Foundations of General Biology

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