Reason for the Correct Answer:
The pKa is a quantitative measure of a weak acid describing its propensity to dissociate into its conjugate base and hydronium ion. The pKa does not change unless a change in temperature occurs.
According to the passage, when carbon dioxide dissolves into blood, carbonic acid is formed.
Carbonic acid will dissociate into (H3O+) and bicarbonate , thus increasing both products in the blood stream.
What occurs when CO2 enters the blood?
A.The in the blood increases.
B.The pKa of the blood decreases.
C.The pH of the blood increases.
D.The [H3O+] in the blood decreases.
A conjugate base is the species formed by the removal of a proton (H+) from its conjugate acid.
Bicarbonate is the conjugate acid.
Bicarbonate, which has a -1 charge, with one proton removed would yield carbonate () , which has a -2 charge.
Which of the following is the conjugate base of bicarbonate?
A.OH–
B.H2CO3
C.
D.
A drop of weak acid will not significantly affect the acidity or basicity of a solution.
According to Figure 1, the titration graph indicates that at a pH level of 8, the equivalence point of the titration is reached. This is the point where the number of moles of added base is equal to the number of moles of the acid in the solution.
A substance that changes color in response to a change in pH levels is an acid-base indicator. Typically added at the start of a titration, a drop of indicator is specifically chosen so that its color change region, near its pKa will approximate the equivalence point of a titration experiment
Before performing the titration represented by the graph in Figure 1, a chemist will add a drop of another weak acid that has a pKa of around 8. What is the likely reason for the addition of this weak acid?
A.The additional acid provides a known starting point to to calibrate the pH of the horizontal portion of the titration graph.
B.The additional acid provides a source of hydronium ions to eliminate the excess hydroxide ions initially in the water.
C.The additional acid maintains the buffering capabilities of the solution against the strong base titrant.
D.The additional acid helps the chemist indicate when the solution passes a certain pH threshold.
The Henderson-Hasselbalch equation relates the weak acid’s pKa the pH level of the solution, the concentration of the weak acid and the concentration of the weak base in a single equation.
A solution containing ten times the concentration of acetic acid as sodium acetate will yield a
Acetic acid has a pKa of 4.8. What is the pH of a solution containing ten times the concentration of acetic acid as sodium acetate?
A.3.8
B.2.2
C.4.2
D.5.8
According to the passage, physiological pH is 7.4.
Amino acids are polyprotic acids with multiple protons, each with their individual pKa values.
When the pH of the solution is greater than the pKa for a proton, the proton is removed and the compound becomes deprotonated at that region. When the pH of the solution is less than the pKa for a proton, the proton remains at that region.
Cysteine has three regions with protons. The carboxylic acid functional group has a pKa (1.71) lower than physiological pH; this region is deprotonated thus carrying a -1 charge. Two of these regions, the thiol and the amine functional groups, have pKa values higher than physiological pH (8.33 and 10.78, respectively); these region are protonated thus carrying a 0 and a +1 charge respectively. The structure of cysteine at a pH of 7.4 is shown here:
Cysteine is a crucial amino acid in the structural support of enzymes. At physiological pH, what is the net charge of the amino acid cysteine?
A.-1
B.0
C.2
D.1
