Biology Chapter 3 Water and Life
How many molecules of glucose (C6H12O6 molecular mass = 180 daltons) would be present in 90 grams of glucose?
(90/180) × 6.02 × 1023
When an ionic compound such as sodium chloride (NaCl) is placed in water, the component atoms of the NaCl crystal dissociate into individual sodium ions (Na+) and chloride ions (Cl-). In contrast, the atoms of covalently bonded molecules (e.g., glucose, sucrose, glycerol) do not generally dissociate when placed in aqueous solution. Which of the following solutions would be expected to contain the greatest number of solute particles (molecules or ions)?
1 L of 1.0 M NaCl
A dietary Calorie equals 1 kilocalorie. Which of the following statements correctly defines 1 kilocalorie?
1,000 calories, or the amount of heat required to raise the temperature of 1 kg of water by 1°C
One liter of a solution of pH 2 has how many more hydrogen ions (H+) than 1 L of a solution of pH 6?
10,000 times more
What is the hydrogen ion [H+] concentration of a solution of pH 8?
10-8 M
One liter of a solution of pH 9 has how many more hydroxyl ions (OH-) than 1 L of a solution of pH 4?
100,000 times more
The molecular weight of water is 18 daltons. What is the molarity of 1 liter of pure water? (Hint: What is the mass of 1 liter of pure water?)
55.6 M
You have a freshly prepared 1 M solution of glucose in water. You carefully pour out a 100 mL sample of that solution. How many glucose molecules are included in that 100 mL sample?
6.02 × 1022
Which of the following effects is produced by the high surface tension of water?
A water strider can walk across the surface of a small pond.
Why does ice float in liquid water?
Hydrogen bonds stabilize and keep the molecules of ice farther apart than the water molecules of liquid water.
A 0.01 M solution of a substance has a pH of 2. What can you conclude about this substance?
It is a strong acid that ionizes completely in water.
Which of the following takes place as an ice cube cools a drink?
Kinetic energy in the drink decreases.
Which of the following ionizes completely in solution and is considered to be a strong base (alkali)?
NaOH
Why does evaporation of water from a surface cause cooling of the surface?
The water molecules with the most heat energy evaporate more readily.
Which of the following statements is true about buffer solutions?
They maintain a relatively constant pH when either acids or bases are added to them.
The slight negative charge at one end of one water molecule is attracted to the slight positive charge of another water molecule. What is this attraction called?
a hydrogen bond
Liquid water's high specific heat is mainly a consequence of the
absorption of heat when hydrogen bonds break.
A given solution contains 0.0001(10-4) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution?
acidic: will give H+ to weak acids, but accept H+ from strong acids
One mole (mol) of glucose (molecular mass = 180 daltons) is
both 180 grams of glucose and 6.02 × 1023 molecules of glucose.
Buffers are substances that help resist shifts in pH by
both donating H+ to a solution when bases are added, and accepting H+ when acids are added.
Water molecules are able to form hydrogen bonds with
compounds that have polar covalent bonds.
If the pH of a solution is decreased from 9 to 8, it means that the
concentration of H+ has increased tenfold (10X) and the concentration of OH- has decreased to one-tenth (1/10) what they were at pH 9.
If the pH of a solution is increased from pH 5 to pH 7, it means that the
concentration of OH- is 100 times greater than what it was at pH 5.
Which of the following solutions would require the greatest amount of base to be added to bring the solution to neutral pH?
gastric juice at pH 2
Which type of bond must be broken for water to vaporize?
hydrogen bonds
A solution contains 0.0000001(10-7) moles of hydroxyl ions [OH-] per liter. Which of the following best describes this solution?
neutral
Hydrophobic substances such as vegetable oil are
nonpolar substances that repel water molecules.
What is the pH of a solution with a hydroxyl ion [OH-] concentration of 10-12 M?
pH 2
In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by
polar covalent bonds.
One of the buffers that contribute to pH stability in human blood is carbonic acid (H2CO3). Carbonic acid is a weak acid that dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). Thus, H2CO3 ↔ HCO3- + H+ If the pH of the blood drops, one would expect
the HCO3- to act as a base and remove excess H+ with the formation of H2CO3.
The partial negative charge in a molecule of water occurs because
the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus.
Temperature usually increases when water condenses. Which behavior of water is most directly responsible for this phenomenon?
the release of heat by the formation of hydrogen bonds
Sulfur is in the same column of the periodic table as oxygen, but has electronegativity similar to carbon. Compared to water molecules, molecules of H2S
will not form hydrogen bonds with each other.
