Chemistry

Chemistry

Problem

A biochemical buffer is being prepared to operate at body temperature (40∘C40^{\circ}\text{C}). The solution is found to contain 5.00×10−6 mol L−15.00\times10^{-6}\,\text{mol}\,\text{L}^{-1} hydroxide ions at this temperature. At 40∘C40^{\circ}\text{C}, the ionic product of water is Kw=2.92×10−14K_w = 2.92\times10^{-14}. (a) Calculate the pOH of the buffer solution at 40∘C40^{\circ}\text{C}, showing every step in your calculation and maintaining correct significant figures. (b) Using the given value of KwK_w, determine the hydronium‐ion concentration and the pH of the solution at 40∘C40^{\circ}\text{C}. Clearly indicate how you incorporate temperature effects into your work. (c) Compare the pH you obtained in part (b) to the pH of neutral water at 40∘C40^{\circ}\text{C}. Explain, with quantitative support, whether the buffer is acidic, neutral, or basic under physiological conditions. (d) Suppose the target pH for the buffer is 7.407.40 at 40∘C40^{\circ}\text{C}. Calculate the factor by which the hydronium‐ion concentration must be adjusted (expressed as a ratio [H3O+]desired/[H3O+]current[\text{H}_3\text{O}^+]_{\text{desired}}/[\text{H}_3\text{O}^+]_{\text{current}}) to achieve the desired pH. Discuss briefly one practical method a chemist might use to implement this adjustment in the laboratory.
Intuitive explanation

This problem tests your understanding that KwK_w changes with temperature—it's not always 10−1410^{-14}. Since you know [OH−][OH^-] and the actual KwK_w at body temperature, you can find [H+][H^+] using the fundamental relationship Kw=[H+][OH−]K_w = [H^+][OH^-], then calculate pH. The key insight is that pH depends on the actual ionization of water at your specific conditions, not a memorized constant.

Intuitive explanation

This problem tests your understanding that KwK_w changes with temperature—it's not always 10−1410^{-14}. Since you know [OH−][OH^-] and the actual KwK_w at body temperature, you can find [H+][H^+] using the fundamental relationship Kw=[H+][OH−]K_w = [H^+][OH^-], then calculate pH. The key insight is that pH depends on the actual ionization of water at your specific conditions, not a memorized constant.

Browse the problem library