Biochemistry Multiple Choice Questions on “Weak Interactions in Aqueous Systems”.
1. What makes water a liquid at room temperature?
A. Hydrogen bonds between water molecules
B. Covalent bonding
C. Noncovalent interactions
D. Van der Waals forces of attraction
Answer: A
Clarification: Hydrogen bonds between water molecules provide the cohesive forces that make water a liquid at room temperature.
2. ΔG is negative for which of the following processes?
A. Melting of ice and evaporation of water
B. Oxidation of nitrogen
C. Oxidation of gold
D. Burning of chlorine
Answer: A
Clarification: The Gibb’s free energy change (ΔG) must have a negative value for a process to occur spontaneously.
Melting of ice and evaporation of water are the two spontaneous processes at room temperature.
3. ΔH is positive for which of the following processes?
A. Oxidation of nitrogen
B. Melting of ice and evaporation of water
C. Oxidation of gold
D. Burning of chlorine
Answer: B
Clarification: Enthalpy change (ΔH) is positive for endothermic reactions, the reactions which involves absorption of energy.
Melting of ice and evaporation of water involves absorption of energy.
4. What is the factor that is responsible for salts like NaCl to dissolve in water easily?
A. Decrease in entropy
B. Increase in entropy
C. Increase in enthalpy
D. Decrease in enthalpy
Answer: B
Clarification: As a salt such as NaCl dissolves, the Na+ and Cl– ions leaves the crystal lattice resulting in an increase in entropy(randomness) of the system which is largely responsible for the ease of dissolving salts such as NaCl in water.
5. What is the heat of vaporization of water?
A. 2260 J/g
B. 2260 kJ/g
C. 1260 J/g
D. 1260 kJ/g
Answer: A
Clarification: The amount of energy needed to change one gram of water to its vapor form at constant temperature is 2260 J/g.
6. The bond dissociation energy of hydrogen bonds in a water molecule is ______________
A. 470 kJ/mole
B. 470 J/mole
C. 23 kJ/mole
D. 23 J/mole
Answer: C
Clarification: The energy required to break the hydrogen bonds (H-H) in water molecule is 23 kJ/mole.
7. The bond dissociation energy of O-H bond in a water molecule is _____________
A. 23 kJ/mole
B. 470 kJ/mole
C. 470 J/mole
D. 23 J/mole
Answer: B
Clarification: The energy required to break O-H bond in a water molecule is more than that required for breaking hydrogen bond, which is 470 kJ/mole.
8. Which of the following is a hypertonic solution?
A. Oceans
B. Freshwater habitats
C. 0.45% sodium chloride
D. Red blood cells placed in fresh water
Answer: A
Clarification: The sea water or oceans are hypertonic to the extracellular fluid of many of the marine organisms. These marine organisms overcome the problem of hyper tonicity by expelling the salt water continuously.
9. Which of the following is a hypotonic solution?
A. 10% dextrose in water
B. 0.45% sodium chloride
C. 5% dextrose in 0.9% sodium chloride
D. Oceans
Answer: B
Clarification: 0.9% normal saline is isotonic and half of 0.9 = 0.45% makes the solution more diluted (contains more water), therefore the solution is hypotonic.
10. Which of the following is an isotonic solution?
A. 0.9% sodium chloride
B. 0.45% sodium chloride
C. Oceans
D. 10% dextrose in water
Answer: A
Clarification: The normal saline solution, 0.9% NaCl has the same salt concentration as the surrounding blood cells.
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