a) How would a too low molarity of NaOH affect the calculated molar mass of the unknown acid? b) How would it affect the calculated Ka of the unknown acid?
If mistakenly calibrated pH meter using pH6 buffer instead of pH7 buffer, all ph meter readings were too low.... how does this affect the molar mass of the unknown acid? would this affect the determined pKa of unknown acid?
I need more information as to the nature of your experiment and the procedure used.
Titration experiment to determine the molar mass and dissociation constant of a weak acid, using NaOH
for a). notice that L x M = moles and moles x molar mass = grams; therefore,
L x M x molar mass = grams and
molar mass = g/(L*M) so M too low means molar mass is too high.
b). Did you use the pH meter to record the pH after drop wise addition of NaOH, then plot the data to find the equivalence point? If so, AND you determined the equivalence point from the plotted data on the graph, the molar mass should not be affected. That's because the equivalence point is determined by the slope ON THE GRAPH. If your instructor told you that the equivalence point would occur at such an such a pH and the pH meter read too low, then L NaOH will be too low. Substitute a too low value for L NaOH in the part a formula we used to get the answer. For the pKa value, no matter how the equivalence point is determined, the pH reading will be too low at the point at which Ka is determined so the pKa will be too low.
a) If the molarity of NaOH is too low, it would affect the calculated molar mass of the unknown acid. To understand why, we need to consider the process of titration. In a titration, a solution of a known concentration (in this case NaOH) reacts with a solution of an unknown concentration (the unknown acid). The reaction between the acid and base is stoichiometric, meaning that the moles of acid and base react in a specific ratio.
To calculate the molar mass of the unknown acid, we rely on the balanced chemical equation and the volume and concentration of the NaOH solution used in the titration. The balanced equation allows us to determine the moles of NaOH required to neutralize the acid. Then, by using the volume and concentration of NaOH, we can determine the moles of the acid.
If the molarity of NaOH is too low, it means there are fewer moles of NaOH available to react with the acid. As a result, the calculated moles of acid will be higher than the actual moles present in the solution. Since molar mass is calculated by dividing the mass by the moles, the molar mass of the unknown acid will be underestimated.
b) The molarity of NaOH does not directly affect the calculated Ka (acid dissociation constant) of the unknown acid. The Ka value represents the degree of ionization or dissociation of an acid in aqueous solution. It is determined by the equilibrium concentration of the acid and its conjugate base.
If the concentration of NaOH is too low and results in an incorrect pH reading, it may indirectly affect the determination of the pKa (negative logarithm of Ka) of the unknown acid. The pKa value is calculated using the Henderson-Hasselbalch equation, which involves the ratio of the concentrations of the acid and its conjugate base. If the pH meter readings are too low due to the calibration error, this could lead to an inaccurate determination of the acid's concentration and, consequently, an incorrect pKa value.
Overall, a too low molarity of NaOH can affect the calculated molar mass of the unknown acid, but its effect on the determined Ka and pKa values depends on the specific experimental setup and calculations used.