CHEM311 Chapter 2: Water and Polarity
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Questions and Answers

What is the purpose of using buffers in a solution?

  • To maintain a stable pH by neutralizing small quantities of additional acid or base (correct)
  • To make the solution more acidic
  • To decrease the pH of the solution
  • To neutralize large quantities of acids or bases

    • In a buffer solution, which component neutralizes a strong base?

  • The spectator ion
  • The strong acid
  • The acid (correct)
  • The conjugate base

    • What is a common buffering agent with a pKa value of 6.40?

  • Citric acid
  • Acetic acid
  • KH2PO4 (correct)
  • Borate

    • In a phosphate buffer system, what is the typical useful pH range?

    <p>6.2 to 8.2</p> Signup and view all the answers

    What is the general rule regarding the effective range of a buffer in relation to its pKa value?

    <p>The effective range is +/- 1 pH unit of the pKa value of the weak acid</p> Signup and view all the answers

    What is a key criterion for selecting a buffer?

    <p>Matching pKa value with the system</p> Signup and view all the answers

    Which of the following is NOT a typical criterion for selecting a buffer?

    <p>High solubility</p> Signup and view all the answers

    What is the principal buffer in cells?

    <p>$H_2PO_4^-/HPO_4^{2-}$</p> Signup and view all the answers

    What happens to blood pH if someone hyperventilates?

    <p>It increases</p> Signup and view all the answers

    If the buffering capacity of a solution is very high, what does that indicate about the concentrations of the weak acid and its conjugate base?

    <p>High concentrations</p> Signup and view all the answers

    What is the pH of a solution after adding 1.5mL of 2.0M HCl to 10.0mL of water?

    <p>5.58</p> Signup and view all the answers

    If you add 1.5mL of 2.0M HCl to a buffer solution, what will happen to the buffer's pH?

    <p>It will decrease</p> Signup and view all the answers

    In a mixture of 0.55M carbonic acid and 0.55M sodium hydrogen carbonate, what is the resulting pH when 1.5mL of 2.0M HCl is added?

    <p>5.84</p> Signup and view all the answers

    How does the addition of HCl impact the concentration of carbonic acid in the mixture of carbonic acid and sodium hydrogen carbonate?

    <p>Increases</p> Signup and view all the answers

    What is the significance of maintaining a specific buffer ratio in a buffer system?

    <p>To neutralize any added acid or base</p> Signup and view all the answers

    What happens when the concentrations of a weak acid and its conjugate base are equal in a solution according to the Henderson-Hasselbalch equation?

    <p>The pH of the solution equals the pKa of the weak acid</p> Signup and view all the answers

    Which type of buffer contains a weak acid and its salt or a weak base and its salt?

    <p>Buffer resistant to pH change</p> Signup and view all the answers

    How do buffers work when a strong base is added to a buffer solution?

    <p>The weak acid absorbs the H+ to neutralize the base</p> Signup and view all the answers

    What happens when a strong acid is added to a buffer solution?

    <p>The pH changes only slightly</p> Signup and view all the answers

    What characterizes a buffer's resistance to changes in pH?

    <p>The ability of the buffer to absorb or release H+ ions without significant changes in pH</p> Signup and view all the answers

    What is the role of a weak acid in an aqueous solution?

    <p>Exists as a conjugate acid-base pair</p> Signup and view all the answers

    How is the strength of an acid described?

    <p>Quantified by Ka value</p> Signup and view all the answers

    Which concept connects the equilibrium constant (K) to the pH of a solution containing both an acid and a base?

    <p>Henderson-Hasselbalch equation</p> Signup and view all the answers

    What is the ionization constant for water at 25°C?

    <p>[H+] * [OH-] = 10^-7</p> Signup and view all the answers

    What is the molar concentration of water used to calculate the ionization constant for water at 25°C?

    <p>55.5 M</p> Signup and view all the answers

    What determines the polarity of a molecule?

    <p>The geometry of the molecule and the polarity of the bonds</p> Signup and view all the answers

    What type of bonds are polar covalent bonds?

    <p>Bonds where electrons are shared but not equally</p> Signup and view all the answers

    What is electronegativity in relation to a compound?

    <p>The ability of an atom in a compound to draw electrons to itself</p> Signup and view all the answers

    How does the geometry of a molecule affect its polarity?

    <p>It can determine whether the molecule is polar or nonpolar</p> Signup and view all the answers

    What does a polar covalent bond imply about electron sharing?

    <p>Electrons are shared but not equally between atoms</p> Signup and view all the answers

    Which type of molecules tend to dissolve in water?

    <p>Hydrophilic</p> Signup and view all the answers

    What type of interactions are very weak between nonpolar molecules?

    <p>Van der Waals interactions</p> Signup and view all the answers

    What kind of molecules have characteristics of both hydrophobic and hydrophilic regions?

    <p>Amphipathic molecules</p> Signup and view all the answers

    What is the term for a spherical arrangement of organic molecules in water solution?

    <p>Micelle</p> Signup and view all the answers

    Which type of bonds are responsible for the attraction between temporary induced dipoles in micelle formation?

    <p>Van der Waals interactions</p> Signup and view all the answers

    What does a Brønsted-Lowry acid donate?

    <p>Proton (hydrogen ion)</p> Signup and view all the answers

    In the context of acids and bases, what does a Brønsted-Lowry base accept?

    <p>Proton (hydrogen ion)</p> Signup and view all the answers

    What is the term for molecules that contain one or more hydrophobic and one or more hydrophilic regions?

    <p>Amphipathic molecules</p> Signup and view all the answers

    What is the main type of bond responsible for forming hydrophobic interactions?

    <p>Van der Waals interactions</p> Signup and view all the answers

    What is the key characteristic of micelles in aqueous solutions?

    <p>Hydrophobic parts on the surface of the sphere</p> Signup and view all the answers

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