Acids and Bases II: Conjugate ions and buffers

A hydronium ion is:

• a.Negatively charged
• b.Able to act as a base
• c.Is created when water takes on a proton
• d.All of the above

In a solution where a reversible reaction is at equilibrium, both the forward and reverse reactions:

• a.Speed up
• b.Slow down
• c.Stop
• d.Continue at the same rate

In a container of pure water at equilibrium:

• a.There are water molecules, hydronium ions, and hydroxide ions
• b.There are only water molecules and hydronium ions
• c.There are only water molecules
• d.There are only hydroxide ions and hydronium ions

From this equilibrium reaction: H3PO4 + H2O <-> H3O+ + H2PO4 <-> H3O+ + HPO4 2 We can see that:

• a.H2PO4 is a strong acid
• b.H2PO4 is amphoteric
• c.Water is a strong base
• d.H3PO4 is amphoteric.

In the reaction: CH3COOH + H¬2O <-> CH¬3COO + H3O+ CH¬3COO is:

• a.A conjugate acid
• b.A conjugate base
• c.In equilibrium with H3O+
• d.Acting as a proton

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:

• a.H3O+ is created by the dissociation of HI
• b.The concentration of H3O+ will be 5 molar
• c.All the HI dissociates.
• d.The HI and I- are in equilibrium

The equilibrium reaction: H3O+ <-> H2O <-> H+ + OH- is important to acid-base chemistry because:

• a.Acid base reactions are always equilibrium reactions
• b.Acids and bases are only found in water
• c.Water determines the pH of a solution
• d.It shows how water can act as both an acid and a base

According to the Bronsted-Lowry definition, NH¬3 is:

• a.A base, because, when it is mixed with water, an OH- ion is created in the resulting solution
• b.A base, because it accepts an H+ ion
• c.An acid, because water donates an H+ ion
• d.An acid, because it contains three hydrogen atoms

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?

• a.The weak acid does not change the pH of the water to any significant degree
• b.The dissolved salt of the weak acid releases a weak conjugate base which can absorb excess protons
• c.The dissolved salt of the weak acid releases a positive ion that acts as a base and can absorb excess protons
• d.The dissolved sodium of the salt exists in equilibrium with any added protons.

Sorenson’s work helped Henderson understand what about the bicarbonate system in the body?

• a.That bicarbonate is a weak acid
• b.That bicarbonate ions, as the weak conjugate base of carbonic acid, and can absorb protons released by bodily processes.
• c.That the bicarbonate system is an equilibrium between carbonic acid, bicarbonate ions, and carbonate ions.
• d.That carbonic acid exists in the body in equilibrium with water