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 systems.
Wow ... 8 posts in 13 minutes, and not a single thought of your own. Please understand that tutors won't do your work for you.
You need to indicate exactly what you have done to work each problem and where you're running into trouble.
I read all of these posts. Almost all are solved with the Henderson-Hasselbalch equation, or some variation of the HH equation. I think all of them are buffer problems. I suggest you pick one of them; e.g. the carbonate/bicarbonate problem, show what you have done or what you think. If you have no idea what to do, explain fully, and in detail, what you don't understand about the problem. Perhaps we can help you through it.
a) The "fellesioneffekten" refers to the property of a substance where it can exist in different forms depending on the pH of the solution. In the case of Veronal, it can exist either in its acidic or ionized form, depending on the pH of the solution.
b) To determine the pH of the solution containing the sodium salt of Veronal, we can use the dissociation constant (Ka) of Veronal. The dissociation constant describes the extent to which a weak acid dissociates in water. In this case, we are given that Ka = 3.7 x 10^-8.
First, let's calculate the concentration of the sodium salt of Veronal in the solution. Since we know that there are 10 mg of the substance and the molecular weight (MW) of NaC8H11N2O3 is 218.18 g/mol, we can calculate the number of moles (n) using the formula:
n = mass / MW
n = 10 mg / 218.18 g/mol
n = 0.0458 mmol
Now, let's calculate the concentration (C) of the sodium salt of Veronal in the solution:
C = n / V
C = 0.0458 mmol / 0.25 L
C = 0.1832 mmol/L
Next, we can set up an equilibrium expression for the dissociation of Veronal:
Ka = [H+][A-] / [HA]
Assuming that all of the sodium salt of Veronal dissociates completely, we can represent the concentrations in terms of the initial concentration, C:
Ka = [H+][A-] / C
Since the sodium salt of Veronal is a weak acid, we can approximate that [H+] is equal to x, where x is the concentration of H+ ions. The concentration of A- ions is also equal to x.
Substituting these values into the equation, we get:
Ka = (x)(x) / C
Solving for x, we can use the quadratic formula:
x = (-b ± √(b^2 - 4ac)) / 2a
In this case, a = 1, b = 0, and c = -Ka*C.
x = (-0 ± √(0^2 - 4(1)(-Ka*C))) / 2(1)
x = (± √(4Ka*C)) / 2
x = (√(4KaC)) / 2
x = √(4KaC) / 2
x = √(4 * 3.7 x 10^-8 * 0.1832 mmol/L) / 2
Calculating this expression, we can find the concentration of H+ ions, which we can later use to calculate the pH of the solution.
c) To determine the solubility of the sodium salt of Veronal in the two buffer systems, we need to consider the pH range in which Veronal remains soluble.
For the 0.5 M KH2PO4 / K2HPO4 buffer system, the pH range will be determined by the pKa values of the two components. KH2PO4 acts as an acid and dissociates to release H+ ions, and K2HPO4 acts as a base and can accept H+ ions. Thus, the buffer system can maintain a stable pH when the pKa values of KH2PO4 and K2HPO4 are in the desired range.
For the 0.5 M NaH2PO4 / Na2HPO4 buffer system, the principle remains the same as the previous buffer system. NaH2PO4 acts as an acid, and Na2HPO4 acts as a base.
To determine which buffer system is more suitable for solubilizing the sodium salt of Veronal, we need to consider the acid-base properties of Veronal itself and the pKa values of the components in the buffer systems. Additionally, the desired pH range for solubility should be considered.
Overall, the solubility of the sodium salt of Veronal in the two buffer systems will depend on various factors, such as the acid-base properties of Veronal and the pKa values of the buffer components. It would require further investigation and experimentation to determine which buffer system is more suitable for solubilizing Veronal.