If a drop of NaOH adhered to the side of the flask and did not get mixed in with
ID: 504383 • Letter: I
Question
If a drop of NaOH adhered to the side of the flask and did not get mixed in with the acetic acid during one of your titrations, would your calculated Molarity of acetic acid in vinegar be larger or smaller than the true value? Why? How many mL of 0.125 M Ba(OH)_2 would be required to completely neutralize 75.0 mL of 0.845 M HCl? What is the pH of the solution at the equivalence point in the titration? A certain indicator changes from blue below pH 5 to green above pH 7. Which of the following types of titrations could this indicator best determine the endpoint: weak acid-strong base, strong acid-strong base titration, or strong acid-weak base? Explain your choice. Comment on the pH meter vs. indicator. Which do you think is better? Why? Support your answer. This question is deliberately vague so you can determine what better means, so to fully support your response, at least a paragraph is expected. You may write your answer on the back.Explanation / Answer
2) (molarity * volume)acid = (molarity * volume)base
If a drop of acid gets adhered to walls of the flask then the volume of the base to reach the equivalence
point will be more. Since concentration of acid is directly proportional to volume of base added, the
molarity of acetic acid in vinegar will be greater than the actual value.
3) 0.125 mol/L * Vol of Ba(OH)2 in L = 0.075 L * 0.845 mol/L
Vol of Ba(OH)2 in L = 0.507 L = 507 mL
Moles of Ba(OH)2 at equivalence point = 0.125 mol/L*0.507 L = 0.063375 moles
Molarity of Ba(OH)2 at equivalence point = 0.063375 moles / (0.075+0.507) = 0.10889M
POH = -log (0.10889) = 0.963
PH + POH = 14
PH = 14-0.963 = 13.04 (rounded off)
4) It is a weak acid - strong base interaction it can be known from the given PH values of indicators
5)PH meter will give accurate values which change with the concentrations, whereas indicators can help you
to estimate certain range of PH values. This is the reason why PH meters are more reliable than indicators.
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