Chapter 2 Practice Problems Flashcards
(13 cards)
Which statement about buffers is true?
-At pH values lower than the pKa, the salt concentration is higher than that of the acid
-When pH=pKa, the weak acid and salt concentration in the buffer are equal
-The strongest buffers are those composed of strong acids and strong bases
-A buffer composed of a weak acid of pKa=5 is stronger at pH 4 than at pH 6
-The pH of a buffered solution remains constant no matter how much acid or base is added to the solution
-When pH=pKa, the weak acid and salt concentration in the buffer are equal
A 1.0M solution of a compound with 2 ionizable groups (pKa’s= 6.2 and 9.5; 100mL total) has a pH of 6.8. If a biochemist adds 60mL of 1.0M HCL to this solution, the solution will change to pH:
8.9
5.6
9.1
4.2
5.6
The pH of a sample of blood is 7.4 while gastric juice is pH 1.4. The blood sample has:
6 times lower [H+] than the gastric juice
One million times lower [H+] than the gastric juice
0.189 times the [H+] as the gastric juice
6000 times lower [H+] as the gastric juice
5.29 times lower [H+] than the gastric juice
One million times lower [H+] than the gastric juice
Osmosis is movement of a :
gas molecule across a membrane
charged solute molecule (ion) across a membrane
nonpolar solute molecule across a membrane
polar solute molecule across a membrane
water molecule across a membrane
water molecule across a membrane
A true statement about hydrophobic interactions is that they:
-primarily involve the effect of polar solutes on the entropy of aqueous systems
-have bonding energies of approximately 20-40 Kjoule per mole
-are the driving force in the formation of micelles of amphipathic compounds in water
-do not contribute to the structure of water-soluble proteins
-involve the ability of water to denature proteins
-are the driving force in the formation of micelles of amphipathic compounds in water
The aqueous solution with the lowest pH is:
0.1M formic acid (pKa= 3.75)
0.01M HCL
10^- 12M NaOH
0.1M acetic acid (pKa= 4.86)
0.1M HCL
0.1M HCL
A compound has a pKa of 7.4. To 100mL of a 1.0M solution of this compound at pH 8.0 is added 30mL of 1.0M hydrochloric acid. The resulting solution is pH:
6.8
7.6
7.4
7.2
6.5
7.4
The pH of a solution of 0.1M NaOH is:
0.1
13
12.8
1
14
13
Dissolved solutes alter some physical (colligative) properties of the solvent water because they change the:
hydrogen bonding of the water
ionic bonding of the water
pH of the water
temperature of the water
concentration of the water
concentration of the water
Which of these statements about hydrogen bonds is not true?
-individual hydrogen bonds in liquid water exist for many seconds and sometimes for minutes
-individual hydrogen bonds are much weaker than covalent bonds
-the strength of a hydrogen bond depends on the linearity of the 3 atoms involved in the bond
-in liquid water, the average water molecule forms hydrogen bonds with 3-4 other water molecules
-hydrogen bonds account for the anomalously high boiling points of water
-individual hydrogen bonds in liquid water exist for many seconds and sometimes for minutes
Phosphoric acid is tribasic, with pKa’s of 2.14, 6.86, and 12.4. The ionic form that predominates at pH 3.2 is:
PO4(-3)
H2PO4(-)
HPPO4(-2)
H3PO4
H2PO4(-)
Which of the following properties of water does not contribute to the fitness of the aqueous environment for living organisms?
Cohesion of liquid water due to hydrogen bonding
The very low molecular weight of water
High heat of vaporization
The density of water is greater than the density of ice
High specific heat
The very low molecular weight of water
The pH of a solution of 1M HCL is:
0
0.1
-1
1
10
0
