Water Biology Chapter 3

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 type of bond must be broken for water to vaporize

hydrogen bonds

Equal volumes (5 mL) of vinegar from a freshly opened bottle are added to each of the following solutions. After complete mixing, which of the mixtures will have the highest pH?

100 mL of household cleanser containing 0.5 M ammonia

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

How many grams of the compound in the figure above would be required to make 1 L of a 0.5 M solution

30

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 x 1022

You have a freshly prepared 0.1 M solution of glucose in water. Each liter of this solution contains how many glucose molecules

6.02 × 1022

A small birthday candle is weighed. It is then lighted and placed beneath a metal can containing 100 mL of water. Careful records are kept as the temperature of the water rises. Data from this experiment are shown on the graph. What amount of heat energy is released in the burning of candle wax? (Note that 1 liter of pure water has a mass of 1 kg.)

0.5 kilocalories per gram of wax burned

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

ssume that acid rain has lowered the pH of a particular lake to pH 4.0. What is the hydroxyl ion concentration of this lake?

1 × 10-10 mol of hydroxyl ion per liter of lake water

What is the hydrogen ion [H+] concentration of a solution of pH 8?

10-8 M

Which of the following ionizes completely in solution and is considered to be a strong base (alkali)?

NaOH

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.

How many molecules of glucose (C6H12O6 molecular mass = 180 daltons) would be present in 90 grams of glucose?

(90/180) × 6.02 × 1023

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

How many grams of the compound in the figure above would be required to make 2.5 L of a 1 M solution? (carbon = 12, oxygen = 16, hydrogen = 1)

150

The molecular weight of water is 18 daltons. What is the molarity of 1 liter of pure water? (Hint: Note that 1 liter of pure water has a mass of 1 kg.)

55.6 M

The molar mass of glucose is 180 g/mol. Which of the following procedures should you carry out to make a 1 M solution of glucose?

Dissolve 180 g of glucose in 0.8 L of water, and then add more water until the total volume of the solution is 1 L.

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.

Which of the following takes place as an ice cube cools a drink?

Kinetic energy in the drink decreases.

What is the pH of a solution with a hydroxyl ion [OH−] concentration of 10-12 M

Ph2

If a solute is in water and only the oxygen parts of water are facing the solute what is the solute's charge?

Positive

Which of these molecules would be soluble in water?

The one with only OHs and Hs

A beaker contains 100 mL of NaOH solution at pH = 13. A technician carefully pours into the beaker 10 mL of HCl at pH = 1. Which of the following statements correctly describes the results of this mixing?

The pH of the beaker's contents will decrease.

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 and release of heat when hydrogen bonds break and form.

One mole (mol) of glucose (molecular mass = 180 daltons) is

both 180 grams of glucose and 6.02 × 1023 molecules of glucose

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.

Research indicates that acid precipitation can damage certain marine organisms by

decreasing the concentration of carbonate ions in oceans.

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

What is the pH of a 1 millimolar NaOH solution

pH 11

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.

Consider two solutions: solution X has a pH of 4; solution Y has a pH of 7. From this information, we can reasonably conclude that

the concentration of hydrogen ions in solution X is 1,000 times as great as the concentration of hydrogen ions in solution Y.

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

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.

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

How many molecules of glycerol (C3H8O3; molecular mass = 92) would be present in 1 L of a 1 M glycerol solution?

6.02 × 1023

You have two beakers. One contains a solution of HCl at pH = 1.0. The other contains a solution of NaOH at pH = 13. Into a third beaker, you slowly and cautiously pour 20 mL of the HCl and 20 mL of the NaOH. After complete stirring, the pH of the mixture will be

7

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.

e molar mass of glucose (C6H12O6) is 180 g/mol. Which of the following procedures should you carry out to make a 0.5 M solution of glucose?

Dissolve 90 g of glucose in a small volume of water, and then add more water until the total volume of the solution is 1 L.

A strong acid like HCl

ionizes completely in an aqueous solution.

Identical heat lamps are arranged to shine on identical containers of water and methanol (wood alcohol), so that each liquid absorbs the same amount of energy minute by minute. The covalent bonds of methanol molecules are nonpolar, so there are no hydrogen bonds among methanol molecules. Which of the following graphs correctly describes what will happen to the temperature of the water and the methanol?

methanol is at a higher rate than water

A solution contains 0.0000001(10-7) moles of hydroxyl ions [OH−] per liter. Which of the following best describes this solution?

neutral

In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by

polar covalent bonds

The nutritional information on a cereal box shows that one serving of a dry cereal has 200 kilocalories. If one were to burn one serving of the cereal, the amount of heat given off would be sufficient to raise the temperature of 20 kg of water how many degrees Celsius?

10.0°C

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.

Increased atmospheric CO2 concentrations might have what effect on seawater?

Seawater will become more acidic, and carbonate concentrations will decrease.

Carbon dioxide (CO2) is readily soluble in water, according to the equation CO2 + H2O ↔ H2CO3. Carbonic acid (H2CO3) is a weak acid. If CO2 is bubbled into a beaker containing pure, freshly distilled water, which of the following graphs correctly describes the results?

Starts at 7 and slowly goes down over time

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 (HCO−3 and a hydrogen ion (H+). Thus, H2CO3 ↔ HCO−3 + 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 HCO−3.

One idea to mitigate the effects of burning fossil fuels on atmospheric CO2 concentrations is to pipe liquid CO2 into the ocean at depths of 2,500 feet or greater. At the high pressures at such depths, CO2 is heavier than water. What potential effects might result from implementing such a scheme?

both increased acidity of the deep waters and changes in the growth of bottom-dwelling organisms with calcium carbonate shells

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 (HCO−3) and a hydrogen ion (H+). Thus, H2CO3 ↔ HCO−3 + H+ If the pH of the blood drops, one would expect

the HCO−3 to act as a base and remove excess H+ with the formation of H2CO3.

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