MCAT Set 5

It is critical for the human body blood to maintain its pH at approximately 7.4. Decreased or increased blood pH are called acidosis and alkalosis respectively; both are serious metabolic problems that can cause death. The table below lists the major buffers found in the blood and/or kidneys. Table 1 Buffer pKa of a typical conjugate acid:* + Histidine side chains Organic phosphates N-terminal amino groups 6.1 6.3 6.8 7.0 8.0 9.2 *For buffers in many of these categories, there is a range of actual values. The relationship between blood pH and the of any buffer can be described by the Henderson- Hasselbalch equation: pH = + log([conjugate base]/[conjugate acid]) Equation 1 Bicarbonate, the most important buffer in the plasma, enters the blood in the form of carbon dioxide, a byproduct of metabolism, and leaves in two forms: exhaled and excreted bicarbonate. Blood pH can be adjusted rapidly by changes in the rate of exhalation. The reaction given below, which is catalyzed by carbonic anhydrase in the erythrocytes, describes how bicarbonate and interact in the blood. + + Reaction 1 The following graph shows the titration of 0.01 M with 10 M NaOH. Within which region of the titration curve will the concentration of become equal to that of ?

It is critical for the human body blood to maintain its pH at approximately 7.4. Decreased or increased blood pH are called acidosis and alkalosis respectively; both are serious metabolic problems that can cause death. The table below lists the major buffers found in the blood and/or kidneys. Table 1 Buffer pKa of a typical conjugate acid:* + Histidine side chains Organic phosphates N-terminal amino groups 6.1 6.3 6.8 7.0 8.0 9.2 *For buffers in many of these categories, there is a range of actual values. The relationship between blood pH and the of any buffer can be described by the Henderson- Hasselbalch equation: pH = + log([conjugate base]/[conjugate acid]) Equation 1 Bicarbonate, the most important buffer in the plasma, enters the blood in the form of carbon dioxide, a byproduct of metabolism, and leaves in two forms: exhaled and excreted bicarbonate. Blood pH can be adjusted rapidly by changes in the rate of exhalation. The reaction given below, which is catalyzed by carbonic anhydrase in the erythrocytes, describes how bicarbonate and interact in the blood. + + Reaction 1 How does the titration of a weak monoprotic acid with a strong base differ from the titration of a strong monoprotic acid with a strong base?

It is critical for the human body blood to maintain its pH at approximately 7.4. Decreased or increased blood pH are called acidosis and alkalosis respectively; both are serious metabolic problems that can cause death. The table below lists the major buffers found in the blood and/or kidneys. Table 1 Buffer pKa of a typical conjugate acid:* + Histidine side chains Organic phosphates N-terminal amino groups 6.1 6.3 6.8 7.0 8.0 9.2 *For buffers in many of these categories, there is a range of actual values. The relationship between blood pH and the of any buffer can be described by the Henderson- Hasselbalch equation: pH = + log([conjugate base]/[conjugate acid]) Equation 1 Bicarbonate, the most important buffer in the plasma, enters the blood in the form of carbon dioxide, a byproduct of metabolism, and leaves in two forms: exhaled and excreted bicarbonate. Blood pH can be adjusted rapidly by changes in the rate of exhalation. The reaction given below, which is catalyzed by carbonic anhydrase in the erythrocytes, describes how bicarbonate and interact in the blood. + + Reaction 1 What would be the nature of the compensatory change that would take place in the respiratory system response to acidosis caused by organic acids?

The mouthpiece of a telephone handset has a mass of 100 g, and the earpiece has a mass of 150 g. To balance the handset on one finger, that finger must be: (Note: Assume the bridge connecting the mouthpiece and the earpiece has a negligible mass.)

The reaction below is NOT spontaneous at any temperature. 2ICl(g) (g) + (g) Which of the following is true?

Which of the following is the reason that water boils at a much higher temperature than does hydrogen sulfide?

In the figure below, aqueous solutions A and B are separated by a semipermeable membrane. Which of the following will occur?

What is the normality of a solution containing 49 g of (MW=98 g/mol) in 2,000 mL of solution?

Band theory explains the conductivity of certain solids by stating that the atomic orbitals of the individual atoms in the solid merge to produce a series of atomic orbitals comprising the entire solid. The closely-spaced energy levels of the orbitals form bands. The band corresponding to the outermost occupied subshell of the original atoms is called the valence band. If partially full, as in metals, it serves as a conduction band through which electrons can move freely. If the valence band is full, then electrons must be raised to a higher band for conduction to occur. The greater the band gap between the separate valence and conduction bands, the poorer the material's conductivity. Figure 1 shows the valence and conduction bands of a semiconductor, which is intermediate in conductivity between conductors and insulators. Figure 1 When silicon, a semiconductor with tetrahedral covalent bonds, is heated, a few electrons escape into the conduction band. Doping the silicon with a few phosphorus atoms provides unbonded electrons that escape more easily, increasing conductivity. Doping with boron produces holes in the bonding structure, which may be filled by movement of nearby electrons within the lattice. When a semiconductor in an electric circuit has excess electrons on one side and holes on the other, electron flow occurs more easily from the side with excess electrons to the side with holes than in the reverse direction. Figure 2 Why is iron a good conductor of electricity?

Band theory explains the conductivity of certain solids by stating that the atomic orbitals of the individual atoms in the solid merge to produce a series of atomic orbitals comprising the entire solid. The closely-spaced energy levels of the orbitals form bands. The band corresponding to the outermost occupied subshell of the original atoms is called the valence band. If partially full, as in metals, it serves as a conduction band through which electrons can move freely. If the valence band is full, then electrons must be raised to a higher band for conduction to occur. The greater the band gap between the separate valence and conduction bands, the poorer the material's conductivity. Figure 1 shows the valence and conduction bands of a semiconductor, which is intermediate in conductivity between conductors and insulators. Figure 1 When silicon, a semiconductor with tetrahedral covalent bonds, is heated, a few electrons escape into the conduction band. Doping the silicon with a few phosphorus atoms provides unbonded electrons that escape more easily, increasing conductivity. Doping with boron produces holes in the bonding structure, which may be filled by movement of nearby electrons within the lattice. When a semiconductor in an electric circuit has excess electrons on one side and holes on the other, electron flow occurs more easily from the side with excess electrons to the side with holes than in the reverse direction. Figure 2 How does heat increase the conductivity of a semiconductor? I) By reducing collisions between moving electrons II) By breaking covalent bonds III) By raising electrons to a higher energy level