S03 Properties of Acids and Bases

What percentage of the human body is composed of water?

60 - 70%.

In what form is a drug diluted upon administration in the body?

A solution.

Which acid-base theory is most appropriate to predict behavior in diluted solutions?

Bornsted-Lowry theory.

Why is understanding acid-base behavior in the body important?

It affects the pharmacokinetic properties of a drug and its compatibility with other molecules.

What type of molecules are most currently used drugs in medicine?

Weak acids or weak bases.

What is the definition of electrolytes?

Charged molecules.

What are strong electrolytes?

Molecules that are completely charged when dissolved in water.

What is an example of a strong electrolyte?

NaCl.

What are weak electrolytes?

Molecules in which the charged and uncharged forms are in equilibrium in solution.

What is an example of a weak electrolyte?

Acetic acid.

What is the definition of an acid?

A proton donor (H+ donor).

What is the definition of a base?

A proton acceptor (H+ acceptor).

What determines the strength of an acid or a base?

The degree of dissociation of that molecule in solutions.

How do strong acids behave in solution?

They dissociate completely.

How do weak acids behave in solution?

They dissociate partially.

What does a single arrow indicate in an acid-base chemical equation?

Complete ionization.

What does an equilibrium arrow indicate in an acid-base chemical equation?

Partial ionization.

How do strong bases behave in solution?

They dissociate completely.

How do weak bases behave in solution?

They dissociate partially.

What is an example of a strong base?

NaOH.

What is an example of a weak base?

NH3.

What does the acid dissociation constant (Ka) measure?

The strength of the acid.

What is the relationship between the strength of an acid and its Ka value?

The stronger the acid, the higher the Ka value.

What is the formula for the acid dissociation constant (Ka)?

Ka = [H3O+][A-]/[HA].

How is pKa calculated from Ka?

pKa = -log Ka.

What does the base dissociation constant (Kb) measure?

The strength of a base.

What is the relationship between the strength of a base and its Kb value?

The stronger the base, the higher the Kb value.

What is the formula for the base dissociation constant (Kb)?

Kb = [BH+][OH-]/[B].

How is pKb calculated from Kb?

pKb = -log Kb.

What molecule can act as both an acid and a base?

Water.

What is the value of the ionization constant of water (Kw) at pure conditions?

1.0 x 10^-14.

What is the equation that relates pKw, pKa, and pKb?

pKw = pKa + pKb.

What is the constant numerical value of pKw?

14.

What is the purpose of the pH scale?

To quantify acidity or basicity of a certain solution.

What is the mathematical definition of pH?

The negative logarithm of hydronium ion concentration, pH = -log[H3O+].

What is the sum of pH and pOH?

pH + pOH = 14.

What is the Henderson-Hasselbalch equation?

pH = pKa + log[A-]/[HA].

In the Henderson-Hasselbalch equation, what does A- always represent?

The conjugate base, whether it is charged or not.

In the Henderson-Hasselbalch equation, what does HA always represent?

The conjugate acid.

What happens to the H+ concentration when an acid is added to water or a neutral salt solution?

A significant increase in H+ concentration is observed, making the solution acidic.

What happens to the OH- concentration when a base is added to water or a neutral salt solution?

A significant increase in OH- ions concentration is observed, making the solution basic.

Why do water and neutral salt solutions undergo significant pH changes when acid or base is added?

Because alone they cannot neutralize or resist changes in pH.

What is a solution called when it cannot resist changes in pH?

Unbuffered.

What are buffers?

A combination of substances that allows an aqueous solution to maintain a desired pH at a relatively constant level when small amounts of acids or bases are added.

What are the components of an acidic buffer system?

A weak acid and the conjugate base of that acid.

What is an example of an acidic buffer system?

Acetic acid and sodium acetate.

What are the components of a basic buffer system?

A weak base and the conjugate acid of that base.

What is an example of a basic buffer system?

Ammonia and ammonium chloride.

When additional base is added to a buffer system, what component neutralizes it?

The weak acid.

When additional acid is added to a buffer system, what component neutralizes it?

The conjugate base.

What is the rule of thumb for the effective buffering range?

pKa ± 1 pH unit.

On a buffer titration curve, at what point does pH = pKa?

When the concentration of conjugate acid equals the conjugate base (HA = A-).

What is the major acid produced by the body that also acts as its own buffer?

Carbonic acid.

What acts as a buffer in the blood to prevent radical changes in blood pH?

The bicarbonate ion.

What is the pKa of the carbonic acid/bicarbonate buffer system?

6.3.

What enzyme catalyzes the reaction between carbon dioxide and water to form carbonic acid?

Carbonic anhydrase.

What primarily maintains intracellular pH?

Inorganic phosphate and proteins.

What is the pKa of the intracellular inorganic phosphate buffer system?

7.2.

How is NH3 produced in the body?

From amino acids catabolism or absorbed through the intestine.

Why must NH3 be maintained at very low concentrations in the blood?

Because it is toxic to neural tissues.

What organ generates and excretes NH3 in the urine in proportion to the acidity of the blood?

The kidney.

What is the pKa of the ammonium urinary buffer system?

9.25.

What acid is secreted by the stomach to ingest proteins?

Hydrochloric acid (HCl).

What neutralizes HCl when stomach contents arrive in the small intestines?

Bicarbonate.

Why is HCl neutralized by bicarbonate in the small intestines?

To prevent the degradation of digestive enzymes by HCl.

At what pH is human blood maintained?

7.4.

What is one of the primary buffer systems in blood plasma?

Carbonic acid/bicarbonate.

What is the relationship between acid strength and pKa values?

The stronger the acid, the lower its pKa value.

What is the primary role of buffers in the body?

To maintain a relatively constant pH.