You prepare a buffer solution from 10.0 mL of 0.100 M MOPS (3-morpholinopropane-1-sulfonic acid) and 10.0 mL of 0.079 M NaOH. Next, you add 1.00 mL of 7.15 × 10-6 M lidocaine to this mixture Denoting lidocaine as L, calculate the fraction of lidocaine present in the form LH
To calculate the fraction of lidocaine (LH) present in the form LH, we need to consider the acid-base equilibrium reaction that occurs between lidocaine (L) and the MOPS buffer solution.
The acid-base equilibrium reaction can be represented as:
L + H2O ⇌ LH + OH-
In this reaction, lidocaine (L) acts as a weak base and reacts with water to form the protonated form LH and hydroxide ion (OH-).
Now, let's calculate the initial concentrations of the species involved:
Initial concentration of L (lidocaine) = 7.15 × 10-6 M (given)
Initial concentration of OH- = concentration of NaOH = 0.079 M (given)
Next, we need to determine the concentrations of L and OH- after the reaction takes place. To do this, we'll assume that lidocaine (L) is completely consumed in the reaction with OH-.
Since 10.0 mL of MOPS buffer and 10.0 mL of NaOH are mixed, the total volume of the solution becomes 20.0 mL or 0.020 L.
Using the initial concentration of lidocaine (L) and the final volume of the solution, we can calculate the final concentration of L as follows:
Final concentration of L = (initial concentration of L * initial volume of L) / final volume of solution
= (7.15 × 10-6 M * 1.00 mL) / 0.020 L
= 3.58 × 10-4 M
Since lidocaine (L) is completely consumed in the reaction with OH-, its final concentration is zero. Therefore, we can determine the final concentration of the protonated form LH as follows:
Final concentration of LH = Initial concentration of L - Final concentration of L
= 7.15 × 10-6 M - 3.58 × 10-4 M
= -3.51 × 10-4 M (negative concentration indicates complete consumption of L)
To calculate the fraction of lidocaine (LH) present in the form LH, we need to divide the final concentration of LH by the initial concentration of L:
Fraction of LH = Final concentration of LH / Initial concentration of L
= (-3.51 × 10-4 M) / (7.15 × 10-6 M)
= -49.02 (rounded to two decimal places)
The fraction of lidocaine (LH) present in the form LH is approximately -49.02, indicating complete conversion of L to LH in the given buffer solution.