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Investigation 14: How Do the Structure and the Initial Conce

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Laura Meng

on 6 April 2015

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Transcript of Investigation 14: How Do the Structure and the Initial Conce

Investigation 14: How Do the Structure and the Initial Concentration of an Acid and a Base Influence the pH of the Resultant Solution During a Titration?
Our Questions:
Given 50 mL of 0.10 M HCl and 50 mL of 0.10 M acetic acid, will the amount of 0.10 M NaOH required to neutralize each solution be the same, more, or less?
Will the pH at the equivalence point of 50 mL 0.10 M HCl be the same, more, or less as the pH at the equivalence points for 50 mL of 0.10 acetic acid?
What are some structural features that might help us classify an acid as a strong acid or weak acid?
Conclusion
For our first question, we needed find out if the amount of base needed to neutralize an acid was equal, more or less to the amount of acid being neutralized. Our group hypothesized that the amount would be the same based on our background research that said in order to reach the equivalence point, the acid and base had to be at equal amounts. Our hypothesis was wrong because in our lab, we found that much more base was needed to neutralize both acids than its equal amount.
Background Research
Equivalence Point: point at which chemically equivalent quantities of acid and base have been mixed
the volume of an added base will equal that of an acid to reach the equivalence point
Background Research
Structural Features that help classify an acid as a strong or weak acid:
charge on the molecule
electronegativity of the attached atom
size of the attached atom
amount of oxygen in similar systems
Other factors: bond strength, polarity, electrical conductivity
Hypothesis
The amount of 0.10 M NaOH needed to neutralize the 50 mL of 0.10 M HCl and 50 mL of 0.10 M acetic acid will be an equal amount to each solution of 50 mL. This is because the volume of the added base needs to be equal to that of the acid to reach an equivalence point.
Background Research
For a strong acid pH, the equivalence point will be a pH of 7
For a weak acid pH, the equivalence point will be above a pH of 7
Hypothesis
The pH at the equivalence point of 50 mL 0.10 M HCl will be lesser than the pH of 50 mL 0.10 M acetic aicd at the equivalence point. This is because HCl is a strong acid while acetic acid is a weak acid.
Hypothesis
Some structural features that can help us classify an acid as a strong or weak acid are the charge on the molecule, the size and electronegativity of its attached atom and the amount of oxygen it has in similar systems. Some others things are weak acids have stronger bonds and are more polar than strong acids. But, strong acids conduct electricity better than weak acids.
For our second question, we were tasked to find out if the pH at the equivalence point for 0.10 M HCl was higher, the same or lower than the pH at the equivalence point for 0.10 M acetic acid, both at equal amounts. Our hypothesis was that the pH of HCl would be lower than that of acetic acid because it is a strong acid while acetic acid is a weak acid. From what we researched, a strong acid should have a pH of around 7 at its equivalence point and a weak acid should have a pH above 7. We found our hypothesis to be true when we looked at our titration graphs. On the titration graph for HCl, the equivalence point was located near the pH of 7 while the equivalence point for acetic acid was located near 7.5.
For our third and final question, we were asked to name some structural features that could help us distinguish a strong acid from a weak acid. Our hypothesis was that you could classify a strong and weak acid by its bond strength, the charge on its molecule, the size and electronegativity of its attached atom and its polarity. We found these factors to be true. Because acetic acid took much longer to reach its equivalence point than HCl, we can assume that its bonds were much harder to break, therefore classifying itself as a weak acid. Our titration graphs support this claim.
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