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 best explains why ice floats on liquid water?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds hold water molecules farther apart in a crystalline lattice.

Question 2

A radioactive isotope of carbon, $$^{14}C$$, is used in medical imaging. What makes $$^{14}C$$ different from the most common carbon isotope, $$^{12}C$$?

Accepted Answer

$$^{14}C$$ has more neutrons than $$^{12}C.$$

Question 3

Which property of water allows a water strider to walk on the surface of a pond?

Accepted Answer

Cohesion due to hydrogen bonding

Question 4

What type of chemical bond is formed when sodium (Na) reacts with chlorine (Cl) to form sodium chloride (NaCl)?

Accepted Answer

Ionic bond

Question 5

Which of the following best describes a polar covalent bond?

Accepted Answer

Electrons are shared unequally, resulting in partial charges on the atoms.

Question 6

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 7

Which of the following elements is NOT a major component (by weight) of the human body?

Accepted Answer

Iron

Question 8

Why is water considered the 'solvent of life'?

Accepted Answer

Water's polarity allows it to dissolve many ionic and polar substances.

Question 9

Which statement best explains why salt (NaCl) dissolves in water?

Accepted Answer

The positive end of water molecules surrounds Cl$$^-$$ ions, and the negative end surrounds Na$$^+$$ ions.

Question 10

Which of the following best describes the role of buffers in biological systems?

Accepted Answer

Buffers maintain a stable pH by binding or releasing hydrogen ions.

Question 11

A neutral atom of sodium (Na) has an atomic number of 11. How many electrons does it have?

Accepted Answer

11

Question 12

Which of the following is a correct chemical equation for the dissociation of water?

Accepted Answer

$$\mathrm{H_2O \rightarrow H^+ + OH^-}$$

Question 13

Which of the following best explains why water has a high specific heat capacity?

Accepted Answer

Hydrogen bonds between water molecules absorb heat when they break and release heat when they form.

Question 14

Which of the following is true about isotopes?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 15

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

Accepted Answer

A molecule is any two or more atoms bonded together, while a compound contains two or more different elements.

Question 16

If a solution changes from pH 6 to pH 4, how does the hydrogen ion concentration change?

Accepted Answer

It increases by 100 times.

Question 17

Which of the following is an example of a hydrogen bond?

Accepted Answer

The attraction between a hydrogen atom of one water molecule and the oxygen atom of another water molecule.

Question 18

Which property of water is most important for the movement of water from roots to leaves in plants?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding

Question 19

Which of the following best describes what happens during a chemical reaction?

Accepted Answer

Atoms are rearranged as bonds are broken and formed.

Question 20

Which of the following is a real-world application of radioactive isotopes in biology?

Accepted Answer

They are used as tracers to monitor the fate of atoms in living organisms.

The Chemical Basis of Life: Elements, Atoms, and Water’s Properties

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