Step-by-Step Problem Solving for First-Year Pharmacy Students
Pharmaceutical Chemistry Department
1
Phosphate Buffer for Liver Enzyme Studies
When studying the activity of the liver enzyme alanine aminotransferase ALT, a phosphate buffer solution is used. To prepare such a solution, 840 ml of 0.1 M sodium hydrogen phosphate is mixed with 160 ml of 0.1 M sodium dihydrogen phosphate solution. Calculate the pH of this solution (pKa(H₂PO₄⁻) = 7.2).
This phosphate buffer is crucial for maintaining the optimal pH for liver enzyme activity studies. The calculated pH (7.92) is within the physiological range where ALT enzyme functions properly, ensuring accurate laboratory results for liver function tests.
The pH of the phosphate buffer solution is 7.92
2
Urine Buffer System Ratios
The pH of human urine normally varies in the range of 4.8–8.0. At what ratios of the volumes of sodium dihydrogen phosphate and sodium hydrogen phosphate is the urine pH 4.5 and 8.5? (pKa(H₂PO₄⁻) = 7.2)
For pH 4.5: 1 part sodium hydrogen phosphate to 500 parts sodium dihydrogen phosphate
For pH 8.5: 20 parts sodium hydrogen phosphate to 1 part sodium dihydrogen phosphate
The phosphate buffer system is important in urine for maintaining pH within physiological limits. These calculations help understand how the body regulates urine pH, which is crucial for kidney function and drug excretion.
For pH 4.5: Volume ratio = 0.002:1
For pH 8.5: Volume ratio = 20:1
3
Blood Alkali Buffer Capacity
Calculate the alkali buffer capacity of blood, if, when adding 1 ml of 0.05 M KOH to 100 ml of blood, the blood pH increases from 7.36 to 7.6.
Step-by-Step Solution:
Understand the buffer capacity formula:
\(\text{Buffer capacity} = \frac{\text{moles of base added}}{\Delta \text{pH} \times \text{volume of solution (L)}}\)
Blood buffer capacity is critical for maintaining physiological pH. This value (2.08 mmol/L·pH) indicates how well blood can resist pH changes when bases are added, which is essential for understanding acid-base balance in clinical practice.
The alkali buffer capacity of blood is 2.08 mmol/L·pH
4
Hemoglobin Forms in Alkalosis
A patient in a state of metabolic alkalosis has the blood pH = 7.6. Calculate for this patient the ratio of the concentrations of deprotonated and protonated forms of hemoglobin in the blood, if pKa(HHb) = 8.2.
The ratio of deprotonated to protonated hemoglobin is 0.251:1
This means there's less deprotonated hemoglobin (Hb⁻) than protonated hemoglobin (HHb)
In alkalosis (high blood pH), hemoglobin tends to hold onto protons more tightly, which affects its oxygen-binding capacity. This ratio is important for understanding how acid-base imbalances impact oxygen transport in the blood.
The ratio of [Hb⁻]/[HHb] = 0.251
5
Blood pH After Adding HCl
The acid buffer capacity of the blood is 50 mmol/L. Calculate the blood pH value after addition of 4.6 ml of 0.05 M HCl to 100 ml of blood with pH = 7.36.
The acid buffer capacity (50 mmol/L) indicates blood's ability to resist pH changes when acids are added. This calculation shows how even small acid additions can affect blood pH, highlighting the importance of buffer systems in maintaining physiological pH balance.
The blood pH after adding HCl is 7.314
6
NaHCO₃ Volume for Target pH
Determine the volume of 0.5 mol/L NaHCO₃ solution that must be added to 50 ml of 0.3 mol/L H₂CO₃ solution so that pH = 4.65 is established in the system, if Ka(H₂CO₃) = 1.7×10⁻⁴.
This calculation is essential for preparing buffer solutions with specific pH values, which is critical in pharmaceutical formulations where precise pH control is needed for drug stability and efficacy.
26.5 mL of 0.5 mol/L NaHCO₃ solution must be added
7
Protein Buffer Capacity Analysis
For the protein (glycine) blood system determine whether the acid or alkali buffer capacity is greater, if it is known that when adding 5 ml of 0.1 M HCl to 10 ml of glycine buffer, its pH decreased by 1.3, and when adding 2 ml 0.25 M NaOH pH increased by 2.4.
The protein (glycine) blood system has greater acid buffer capacity than alkali buffer capacity.
This asymmetry in buffer capacity is common in biological systems. The greater acid buffer capacity helps the body better handle acid loads, which is important for understanding how protein buffers protect against acidosis in clinical practice.
Acid buffer capacity is greater than alkali buffer capacity
8
Ammonium Buffer pH Calculation
Calculate the pH of an ammonium buffer of urine containing 15 ml of 0.5 M NH₄Cl and 35 ml of 0.85 M NH₄OH after adding 5 ml of 0.1 M NaOH (Ka(NH₄OH) = 5.62×10⁻¹⁰).
Ammonium buffers are important in urine for maintaining pH balance. This calculation shows how buffer systems respond to base addition, which is critical for understanding renal acid-base regulation and drug excretion mechanisms.
The pH of the ammonium buffer after adding NaOH is 9.89