Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
28 Cards in this Set
- Front
- Back
|
What are buffer systems? |
Compounds, that by their presence in a solution, resist changes in pH after the addition of small amounts of acids and bases |
|
|
What are acid buffers made of? |
weak acid and its conjugate base(salt) |
|
|
What are basic buffers made of? |
weak base and its conjugate acid(salt) |
|
|
What should stay the same when a buffer resists the change? |
The number of hydrogen and hydroxyl ions |
|
|
What is the Henderson-Hasselbach equation for acid buffers? |
pH = pKa + log [salt]/[acid] *salt is ionized *acid is unionized |
|
|
What is the Henderson-Hasselbach equation for basic buffers? |
pH = pKa + log [base]/[salt] *salt is ionized *base is unionized |
|
|
The pH of a buffer is affected only by... |
the ratio of concentration of salt over acid or base since the dissociation constant is a constant |
|
|
If the ratio of salt over acid or base over salt is identical... |
the pH will remain unaffected regardless of the molar concentrations of salt and acid |
|
|
Conjugate acid base pair may act as... |
a proton donator and acceptor |
|
|
What is the most important rule to remember when choosing a buffer? |
Always choose a buffer within range where pH = pKa +/- 2 |
|
|
Buffering action by a given acid-base pair is possible over a limited range. What 4 things is it limited by? |
*pH desired *pKa or pKb *concentration of buffering agents *chemical stability of buffering agents |
|
|
What do buffers protect against? |
They protect preparations from large swings in pH, but there is a limit through which the buffers are effective. |
|
|
What is buffer capacity? |
The strength of a buffer, or buffer value, or buffer effect *the ratio of change in gram equivalent weight of an acid or bas needed to produce a particular change in pH in 1 L of buffer solution |
|
|
What is the buffer capacity, Van Slyke equation? |
Buffer capacity=2.3C * (Ka*[H+])/ ((Ka+[H+]))^2 *C=molar concentration of buffer |
|
|
What is the equation to calculate buffer capacity regarding gram equivalent weight in 1 L of buffer solution? |
buffer capacity = B/change in pH *B is Eq/L of acid or base added that caused the change in pH |
|
|
What is the equation for maximum buffer capacity? When does buffer capacity reach its maximum? |
buffer capacity = 0.575 C It reaches its maximum when ka=[H+] |
|
|
What does the capacity of a buffer depend on? |
*ionic dissociation constant *hydrogen ion concentration *molar concentration of a buffer |
|
|
What are the units for buffer capacity? |
gram Eq/liter^-1.pH^-1 *no units are usually stated for buffer capacity |
|
|
What 5 steps should you take when preparing a buffer? |
1. Decide what pH is needed 2. Choose the acid-base pair so that Ka is close to [H+] for max buffer capacity 3. Use Hend-Hass equation to determine ratio of proton acceptor to donor **4. Choose total conc. of acid-base pair so that buffer capacity falls in range 0.01-0.1 5. Verify pH of prepared buffer |
|
|
Most drugs are classified as what? |
organic weak electrolytes |
|
|
Ionization of weak electrolytes has what type of relationship with pH |
It is dependent on pH |
|
|
A drug will exist in unionized or ionized form depending on what? |
pH |
|
|
Which is more soluble in aqueous solutions, ionized or unionized form? |
ionized form is relatively more soluble |
|
|
Which is more lipid soluble, ionized or unionized? |
Unionized is relatively more lipid soluble--meaning it is more permeable through lipid membranes |
|
|
Change in pH corresponds to changes in what three properties? |
*solubility *dissolution rate *partition coefficient |
|
|
Degree of ionization can have a profound effect on what properties? |
*absorption *distribution *elimination of drugs |
|
|
What 3 times are buffers used? |
*drug stability studies *diffusion-dissolution studies *partitioning studies |
|
|
Physiologic buffer in the blood and eye keep the pH at what level? What are some examples of buffers in the blood and eye? |
7.4 both in blood and eye Blood: hemoglobin, bicarbonate, phosphates, plasma proteins, etc Eye: proteins, carbonic acid, organic acid in tears |
