Quiz 3 Water
Measurements show that the pH of a particular lake is 4.0. What is the hydroxide ion concentration of the lake?
10-10 M
Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake?
10-4 M
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.
You have two beakers. One contains pure water, the other contains pure methanol (wood alcohol). The covalent bonds of methanol molecules are nonpolar, so there are no hydrogen bonds among methanol molecules. You pour crystals of table salt (NaCl) into each beaker. Predict what will happen.
NaCl crystals will dissolve readily in water but will not dissolve in methanol
One of the buffers that contribute to pH stability in human blood is carbonic acid (H2CO3). Carbonic acid is a weak acid that, when placed in an aqueous solution, dissociates into a bicarbonate ion (HCO3- and a hydrogen ion (H+). Thus, H2CO3 HCO3- + H+ If the pH of the blood increases, one would expect
a decrease in the concentration of H2CO3 and an increase in the concentration of HCO3-.
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
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
The bonds that are broken when water vaporizes are
hydrogen bonds between water molecules.
A strong acid like HCl
ionizes completely in an aqueous solution.
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.
Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability of sweat to lower body temperature?
the absorption of heat by the breaking of hydrogen bonds
If a solution has a pH of 7, this means that
the concentration of H+ ions in the water equals the concentration of OH- ions in the water.
If the cytoplasm of a cell is at pH 7, and the mitochondrial matrix is at pH 8, this means that
the concentration of H+ ions is tenfold higher in the cytoplasm than in the mitochondrial matrix.
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
Research indicates that acid precipitation can damage living organisms by
washing away certain mineral ions that help buffer soil solution and are essential nutrients for plant growth.
Which of the following is a hydrophobic material?
wax
Liquid water's high specific heat is mainly a consequence of the
absorption and release of heat when hydrogen bonds break and form.
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
Increased atmospheric CO2 concentrations might have what effect on seawater?
Seawater will become more acidic, and carbonate concentrations will decrease.
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.
How would acidification of seawater affect marine organisms?
Acidification would decrease dissolved carbonate concentrations and hinder growth of corals and shell-building animals.
Carbon dioxide (CO2) is readily soluble in water, according to the equation CO2 + H2O H2CO3. Carbonic acid (H2CO3) is a weak acid. Respiring cells release CO2 into the bloodstream. What will be the effect on pH of blood as that blood first comes in contact with respiring cells?
Blood pH will decrease slightly.
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.
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.
