Problem 1
Effect of Local Environment on Ionic Bond Strength The ATP-binding site of an enzyme is buried in the interior of the enzyme, in a hydrophobic environment. Suppose that the ionic interaction between enzyme and ATP took place at the surface of the enzyme, exposed to water. Would this enzymesubstrate interaction be stronger or would it be weaker? Why?
Problem 2
Biological Advantage of Weak Interactions The associations between biomolecules are often stabilized by hydrogen bonds, electrostatic interactions, the hydrophobic effect, and van der Waals interactions. How are weak interactions such as these advantageous to an organism?
Problem 3
Solubility of Ethanol in Water Ethane \(\left(\mathrm{CH}_{3} \mathrm{CH}_{3}\right)\) and ethanol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right)\) differ in their molecular makeup by only one atom, yet ethanol is much more soluble in water than ethane. Describe the features of ethanol that make it more water soluble than ethane.
Problem 4
That is the \(\mathrm{pH}\) of a solution that has an \(\mathrm{H}^{+}\)concentration of a. \(1.75 \times 10^{-5} \mathrm{~mol} / \mathrm{L}\); b. \(6.50 \times 10^{-10} \mathrm{~mol} / \mathrm{L}\); c. \(1.0 \times 10^{-4} \mathrm{~mol} / \mathrm{L}\); d. \(1.50 \times 10^{-5} \mathrm{~mol} / \mathrm{L}\) ?
Problem 5
Calculation of Hydrogen Ion Concentration from \(\mathrm{pH}\) What is the \(\mathrm{H}^{+}\)concentration of a solution with \(\mathrm{pH}\) of a. \(3.82\); b. \(6.52\); c. \(11.11\) ?
Problem 6
8 Acidity of Gastric HCl A technician in a hospital laboratory obtained a \(10.0 \mathrm{~mL}\) sample of gastric juice from a patient several hours after a meal and titrated the sample with \(0.1 \mathrm{~m} \mathrm{NaOH}\) to neutrality. The neutralization of gastric \(\mathrm{HCl}\) required \(7.2 \mathrm{~mL}\) of \(\mathrm{NaOH}\). The patient's stomach contained no ingested food or drink at the time of sample harvest. Therefore, assume that no buffers were present. What was the \(\mathrm{pH}\) of the gastric juice?
Problem 7
Calculation of the \(\mathrm{pH}\) of a Strong Acid or Base a. Write out the acid dissociation reaction for hydrochloric acid. b. Calculate the \(\mathrm{pH}\) of a solution of \(5 \times 10^{-4} \mathrm{M}\) hydrochloric acid at \(25^{\circ} \mathrm{C}\). c. Write out the acid dissociation reaction for sodium hydroxide. d. Calculate the \(\mathrm{pH}\) of a solution of \(7 \times 10^{-5} \mathrm{M}\) sodium hydroxide at \(25^{\circ} \mathrm{C}\).
Problem 8
Calculation of \(\mathrm{pH}\) from Concentration of Strong Acid Calculate the \(\mathrm{pH}\) of a solution prepared by diluting \(3.0 \mathrm{~mL}\) of \(2.5 \mathrm{M} \mathrm{HCl}\) to a final volume of \(100 \mathrm{~mL}\) with \(\mathrm{H}_{2} \mathrm{O}\).
Problem 9
Measurement of Acetylcholine Levels by pH Changes You have a \(15 \mathrm{~mL}\) sample of acetylcholine (a neurotransmitter) with an unknown concentration and a \(\mathrm{pH}\) of \(7.65\). You incubate this sample with the enzyme acetylcholinesterase to convert all of the acetylcholine to choline and acetic acid. The acetic acid dissociates to yield acetate and hydrogen ions. At the end of the incubation period, you measure the \(\mathrm{pH}\) again and find that it has decreased to \(6.87\). Assuming there was no buffer in the assay mixture, determine the number of nanomoles of acetylcholine in the original \(15 \mathrm{~mL}\) sample.
Problem 10
Relationship Between \(\mathrm{p} K_{\text {a }}\) and pH Which aqueous solution has the lowest pH: \(0.1 \mathrm{~m}\) hydrofluoric acid \(\left(\mathrm{p} K_{\mathrm{a}}=3.20\right) ; 0.1 \mathrm{M}\) acetic acid \(\left(\mathrm{p} K_{\mathrm{s}}=4.86\right) ; 0.1 \mathrm{~m}\) formic acid \(\left(\mathrm{p} K_{\mathrm{a}}=3.75\right) ;\) or \(0.1 \mathrm{~m}\) lactic acid \(\left(\mathrm{p} K_{\mathrm{a}}=7.86\right) ?\)
