Biol 1441: Exam 3
34 Cards in this Set
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In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by
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polar covalent bonds
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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?
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a hydrogen bond
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The partial negative charge in a molecule of water occurs because
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the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus.
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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
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will not form hydrogen bonds with each other.
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Water molecules are able to form hydrogen bonds with
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compounds that have polar covalent bonds.
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Which of the following effects is produced by the high surface tension of water?
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A water strider can walk across the surface of a small pond.
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Which of the following takes place as an ice cube cools a drink?
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Kinetic energy in the drink decreases.
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A dietary Calorie equals 1 kilocalorie. Which of the following statements correctly defines 1 kilocalorie?
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1,000 calories, or the amount of heat required to raise the temperature of 1 kg of water by 1°C
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Liquid water's high specific heat is mainly a consequence of the
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absorption of heat when hydrogen bonds break.
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Which type of bond must be broken for water to vaporize?
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hydrogen bonds
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Temperature usually increases when water condenses. Which behavior of water is most directly responsible for this phenomenon?
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the release of heat by the formation of hydrogen bonds
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Why does evaporation of water from a surface cause cooling of the surface?
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The water molecules with the most heat energy evaporate more readily.
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Why does ice float in liquid water?
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Hydrogen bonds stabilize and keep the molecules of ice farther apart than the water molecules of liquid water.
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Hydrophobic substances such as vegetable oil are
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nonpolar substances that repel water molecules.
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One mole (mol) of glucose (molecular mass = 180 daltons) is
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both 180 grams of glucose and 6.02 × 1023 molecules of glucose.
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How many molecules of glucose (C6H12O6 molecular mass = 180 daltons) would be present in 90 grams of glucose?
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(90/180) × 6.02 × 1023
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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…
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1 L of 1.0 M NaCl
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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?)
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55.6 M
Solution: 1 liter of water weighs 1000g. 1M of water should have 18g of water, therefore 1000g of pure water should have molarity of 1000/18 = 55.6.
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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?
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6.02 × 1022
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Which of the following ionizes completely in solution and is considered to be a strong base (alkali)?
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NaOH
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A 0.01 M solution of a substance has a pH of 2. What can you conclude about this substance?
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It is a strong acid that ionizes completely in water.
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A given solution contains 0.0001(10-4) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution?
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acidic: will give H+ to weak acids, but accept H+ from strong acids
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A solution contains 0.0000001(10-7) moles of hydroxyl ions [OH-] per liter. Which of the following best describes this solution?
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neutral
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What is the pH of a solution with a hydroxyl ion [OH-] concentration of 10-12 M?
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pH 2
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Which of the following solutions would require the greatest amount of base to be added to bring the solution to neutral pH?
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gastric juice at pH 2
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What is the hydrogen ion [H+] concentration of a solution of pH 8?
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10-8 M
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If the pH of a solution is decreased from 9 to 8, it means that the
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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.
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If the pH of a solution is increased from pH 5 to pH 7, it means that the
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concentration of OH- is 100 times greater than what it was at pH 5.
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If the pH of a solution is increased from pH 5 to pH 7, it means that the
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concentration of OH- is 100 times greater than what it was at pH 5.
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One liter of a solution of pH 2 has how many more hydrogen ions (H+) than 1 L of a solution of pH 6?
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10,000 times more
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One liter of a solution of pH 9 has how many more hydroxyl ions (OH-) than 1 L of a solution of pH 4?
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100,000 times more
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Which of the following statements is true about buffer solutions?
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They maintain a relatively constant pH when either acids or bases are added to them.
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Buffers are substances that help resist shifts in pH by
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both donating H+ to a solution when bases are added, and accepting H+ when acids are added.
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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+
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the HCO3- to act as a base and remove excess H+ with the formation of H2CO3.
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Biol 1441: Chapter 12