a) What is fellesioneffekten?

 
Veronal is a barbiturate (structure see above). Barbiturates is a substance class which occur in a variety of drug classes, including sleep medications (hypnotikasedativa), in painkillers (anesthetics) and anticonvulsants. A barbiturate is a weak acid. Veronal is usually given in the form of its sodium salt.
 
b) Determine the pH of a 250 mL solution containing 10 mg of sodium salt of veronal with molecular formula NaC8H11N2O3? For Veronal is Ka = 3.7 x 10-8.
 
c) As a pharmacist wants you to solve the sodium salt of veronal in a buffer, and you can choose between these two possibilities: i) 0.5M KH2PO4 / K2HPO4 or ii) 0.5 M NaH2PO4 / Na2HPO4. Discuss solubility of sodium salt of veronal in the two buffer

a) The fellesioneffekten is the Swedish term for the "common ion effect" in English. It refers to the phenomenon where the presence of a common ion in a solution suppresses the ionization of a weak acid or weak base.

b) To determine the pH of the solution containing the sodium salt of veronal, we need to calculate the concentration of the veronal's weak acid form (HC8H11N2O3) and its conjugate base form (C8H11N2O3⁻). From the molecular formula, we can see that the veronal's sodium salt (NaC8H11N2O3) dissociates into Na+ ions and C8H11N2O3⁻ ions in solution. Since the sodium salt is a strong electrolyte, it completely dissociates. Therefore, the molar concentration of C8H11N2O3⁻ is equal to the molar concentration of NaC8H11N2O3.

First, we need to convert the mass of the sodium salt (10 mg) to moles. The molar mass of the sodium salt can be calculated by adding the molar masses of each element: 22.99 g/mol (Na) + 8.00 g/mol (C) + 11.01 g/mol (H) + 14.01 g/mol (N) + 2(16.00 g/mol) (O) = 235.01 g/mol.

Next, we can find the molar concentration of the sodium salt using the formula: molarity (M) = moles of solute / volume of solution (L). Since the given volume is 250 mL, we convert it to liters by dividing by 1000: 250 mL / 1000 mL/L = 0.250 L.

Now, we can calculate the molar concentration of the sodium salt: moles of solute = mass of solute / molar mass = 10 mg / 235.01 g/mol = 0.0426 mmol.
Therefore, the molar concentration is: 0.0426 mmol / 0.250 L = 0.1704 M.

The veronal's weak acid (HC8H11N2O3) and its conjugate base (C8H11N2O3⁻) are in a 1:1 ratio with the sodium salt since they all come from the dissociation of the sodium salt. Therefore, the molar concentrations of the weak acid and conjugate base are both 0.1704 M.

To calculate the pH, we can use the Henderson-Hasselbalch equation:
pH = pKa + log([C8H11N2O3⁻] / [HC8H11N2O3])

Given the pKa of veronal (Ka = 3.7 x 10⁻⁸), we can calculate the pH:
pH = -log(3.7 x 10⁻⁸) + log(0.1704 / 0.1704)
pH = 7.43

Therefore, the pH of the solution containing the sodium salt of veronal is approximately 7.43.

c) To discuss the solubility of the sodium salt of veronal in the two buffer solutions, we need to consider the common ion effect. The 0.5M KH2PO4 / K2HPO4 buffer contains the common ion "PO4⁻³" from both the weak acid form (KH2PO4) and its conjugate base form (K2HPO4). Similarly, the 0.5M NaH2PO4 / Na2HPO4 buffer contains the common ion "PO4⁻³" from both the weak acid form (NaH2PO4) and its conjugate base form (Na2HPO4).

Since the sodium salt of veronal contains the ion "C8H11N2O3⁻," we need to consider whether the presence of these common ions will affect its solubility. The common ion effect reduces the solubility of a compound when a common ion is present in the solution.

In this case, the presence of the common ion "PO4⁻³" from the buffers will decrease the solubility of the sodium salt of veronal. Therefore, neither of the two buffers would be favorable for solving the sodium salt of veronal, as the presence of the common ion would limit its solubility.

It may be necessary to explore other buffer solutions or solubility-enhancing techniques to effectively dissolve the sodium salt of veronal.