How would the calculated value of the molar mass of an unknown acid be affected (higher, lower, or no change) if the following occurs?
(a) The pH meter was incorrectly calibrated to read lower than the actual pH.
(b) During the titration, several drops of NaOH missed the reaction beaker and fell onto the bench top.
(c) Acid was dissolved in 75 mL of distilled water rather than 50 mL.
The answers depends upon what you are doing and you don't provide enough information; however, here is my best guess as to what is going on.
You must be titrating an acid with a base(NaOH). The mols base used = M x L and you know both M and L. You are using the pH meter to know when you've reached the equivalence point.
Here are the two equations you're using.
equation 1 is M x L = moles NaOH = moles acid.
equation 2 is molar mass = grams/moles.
Now we subject these two equations to the problems.
a. pH meter reads lower (meaning it reads more acidic than the solution actually is) so you must add more base to get to the equivalence. More mL base = a higher number from equation 1 and if you plug a high number of mols into equation 2, that means a lower molar mass is calculated.
b. NaOH missed the mark means more must be added to reach equivalence point, more mL from equation means more moles to equation 2 and smaller molar mass.
c. I don't know what you did in c. If you weighed out a solid acid, placed ALL of it into the beaker, then added 75 instead of 50 mL, the molar mass will be affected because you've titrated all of the sample weighed. If, however, you weighed out the solid acid, placed it in the beaker, added 75 instead of 50 mL, then transferred a PORTION of that to titrate, then you transferred less than intended because of the dilution, that means fewer mL to reach the equivalence point, moles from equation 1 will be a smaller number and a smaller value for moles in equation 2 means a larger molar mass.
Hope this helps.
(a) If the pH meter was incorrectly calibrated to read lower than the actual pH, the calculated value of the molar mass of the unknown acid would be affected by inflating the ego of the acid, leading to a higher value. It would be like the acid wearing high heels to make itself appear taller.
(b) If during the titration, several drops of NaOH missed the reaction beaker and fell onto the bench top, well, we can just hope that the bench top enjoys the company of NaOH. However, this mishap would have no effect on the calculated value of the molar mass of the unknown acid. It's like trying to measure the weight of a fish, but accidentally dropping some potatoes on the scale instead. The fish won't be affected.
(c) If the acid was dissolved in 75 mL of distilled water rather than 50 mL, the calculated value of the molar mass of the unknown acid would be lower. It's like diluting your coffee with too much milk, making it weaker and less flavorful. So, in this case, the acid becomes a little less special and its molar mass decreases.
(a) If the pH meter was incorrectly calibrated to read lower than the actual pH, it would not directly affect the calculated value of the molar mass of the unknown acid. The pH meter measures the acidity of the solution, but the molar mass is determined through the titration process.
(b) If several drops of NaOH missed the reaction beaker and fell onto the bench top during the titration, it would not directly affect the calculated value of the molar mass. The molar mass is determined based on the amount of acid that reacted with the base, not the amount of base used. As long as the acid was properly measured and reacted fully with the base, the molar mass calculation should not be affected.
(c) If the acid was dissolved in 75 mL of distilled water rather than 50 mL, it would lead to a higher calculated value of the molar mass. The molar mass is determined based on the concentration of the acid, which is calculated by dividing the moles of acid by the volume of the solution. If the volume of the solution is increased, the calculated concentration of the acid will be lower, resulting in a higher calculated molar mass.
To determine how each of these scenarios would affect the calculated value of the molar mass of an unknown acid, we need to understand the experiments involved.
In titration experiments, a known concentration of a base is added slowly to an acid until the solution reaches the equivalence point, where the reaction is complete. This allows us to determine the molar mass of the acid based on the amount of base required to neutralize it.
Now let's analyze each scenario:
(a) The pH meter was incorrectly calibrated to read lower than the actual pH.
If the pH meter is reading lower than the actual pH, it means the measured pH values during the titration will be lower than their actual values. As a result, the apparent endpoint will be reached earlier because the pH change caused by the acid and base reaction will be underestimated. This will lead to an incorrect determination of the amount of base required to neutralize the acid. The calculated molar mass of the acid would be lower than the actual value.
(b) During the titration, several drops of NaOH missed the reaction beaker and fell onto the bench top.
If some drops of NaOH missed the reaction beaker and fell onto the bench top, it means less NaOH would react with the acid in the beaker, resulting in a decreased volume of NaOH solution used for the titration. Consequently, less base will be recorded in the data, and the calculated molar mass of the acid would be higher than the actual value.
(c) Acid was dissolved in 75 mL of distilled water rather than 50 mL.
If the acid is dissolved in a larger volume of distilled water than prescribed, it will result in a more diluted acid solution. This means that more moles of acid will be required to reach the same concentration compared to if it were dissolved in less water. As a result, more base will be consumed during the titration to neutralize the acid, leading to a higher calculated molar mass for the acid.
In summary:
(a) If the pH meter is calibrated to read lower than the actual pH, the calculated molar mass of the acid will be lower.
(b) If some drops of NaOH missed the reaction beaker, the calculated molar mass of the acid will be higher.
(c) If the acid is dissolved in a larger volume of distilled water, the calculated molar mass of the acid will be higher.