Chemical Relationships Acids and Bases II: Conjugate ions and buffers by Robin Marks, M.A. Reading Quiz Teach with this 1. A hydronium ion is: Negatively charged Able to act as a base Is created when water takes on a proton All of the above 2. In a solution where a reversible reaction is at equilibrium, both the forward and reverse reactions: Speed up Slow down Stop Continue at the same rate 3. In a container of pure water at equilibrium: There are water molecules, hydronium ions, and hydroxide ions There are only water molecules and hydronium ions There are only water molecules There are only hydroxide ions and hydronium ions 4. From this equilibrium reaction: H3PO4 + H2O <-> H3O+ + H2PO4 <-> H3O+ + HPO4 2 We can see that: H2PO4 is a strong acid H2PO4 is amphoteric Water is a strong base H3PO4 is amphoteric. 5. In the reaction: CH3COOH + H¬2O <-> CH¬3COO + H3O+ CH¬3COO is: A conjugate acid A conjugate base In equilibrium with H3O+ Acting as a proton 6. 6. Once 5 moles of hydroiodic acid, HI, is mixed into 1L water, there are only products, and no HI remains. HI -> H3O+ + I- We consider HI to be a strong acid because: H3O+ is created by the dissociation of HI The concentration of H3O+ will be 5 molar All the HI dissociates. The HI and I- are in equilibrium 7. The equilibrium reaction: H3O+ <-> H2O <-> H+ + OH- is important to acid-base chemistry because: Acid base reactions are always equilibrium reactions Acids and bases are only found in water Water determines the pH of a solution It shows how water can act as both an acid and a base 8. According to the Bronsted-Lowry definition, NH¬3 is: A base, because, when it is mixed with water, an OH- ion is created in the resulting solution A base, because it accepts an H+ ion An acid, because water donates an H+ ion An acid, because it contains three hydrogen atoms 9. 9. While studying the acid-base reactions of the bicarbonate system, Danish chemist Soren Sorenson noticed that adding a weak acid and its sodium salt made a solution that resists changes in pH. What explains this buffering phenomenon? The weak acid does not change the pH of the water to any significant degree The dissolved salt of the weak acid releases a weak conjugate base which can absorb excess protons The dissolved salt of the weak acid releases a positive ion that acts as a base and can absorb excess protons The dissolved sodium of the salt exists in equilibrium with any added protons. 10. Sorenson’s work helped Henderson understand what about the bicarbonate system in the body? That bicarbonate is a weak acid That bicarbonate ions, as the weak conjugate base of carbonic acid, and can absorb protons released by bodily processes. That the bicarbonate system is an equilibrium between carbonic acid, bicarbonate ions, and carbonate ions. That carbonic acid exists in the body in equilibrium with water Score Quiz
