IntroAcids - Group Report Template

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University of New Hampshire *

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Chemistry

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Apr 3, 2024

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Acids, Bases, and pH Group Report Include your name and your lab partner’s name and submit the same file to both partners’ Canvas accounts if and only if both of you collaborated on this report. Do not modify or remove the question text. Do not use bold font in your answers. Do not use red text in your answers. Module 1 Acid Strength 1. Include a copy of the plot of log(conductivity) vs. pH. Table 1. Log(conductivity) vs. pH. 2. Describe the trend your data shows between log(conductivity) and pH does your data show. The data shows a downward trend between log(conductivity) and pH. As pH increases, log(conductivity) decreases. 3. Which of the acids in this module are strong acids? You can look up a list of common strong acids in almost any chemistry resource . Sulfuric acid, Nitric acid, HC. 4. Explain why you should expect most strong acids to give the same pH as each other if they are prepared at the same concentration. If the strong acids have the same molarity, they will have the same concentration of H + ions, therefore, the same pH.

5. Your measurement sulfuric acid in water should have a slightly lower pH than other strong acids. What is different about sulfuric acid that would explain this? ( Hint: Look at the molecular formula of sulfuric acid.) Unlike many of the other acids, sulfuric acid has two ionizable hydrogens for every molecule, giving it a low pH. Module 2 Acids, Bases, and Salts 6. Compare the indicated pH of each species in module 2 to that of water and indicate for each of the first 12 species, which are acidic, basic, and neutral compared to water. The acidic species are HC 2 H 3 O 2 , Fe(NO 3 ) 3 , HNO 3 , and Al(NO 3 ), the basic species are NaOH, NaC 2 H 3 O 2 , Na 2 CO 3 , NaHCO 3 , Na 3 PO 4 , and NH 4 OH, the neutral species are H 2 O and NaCl. Similarly, some bases are easily identified by the presence of the hydroxide ion directly in their formula. 7. Many acidic compounds have a loosely bound hydrogen atom that can be easily donated as an H + ion. a. Which of the Module II compounds fit(s) this description? Some of the module II compounds that fit this description are HNO 3 and Al(NO 3 ) 3 . Both compounds are strong acids and will easily donate H+ ions. On the other hand, other acidic compounds such as HC 2 H 3 O 2 are weak acids, or acidic salts such as Fe(NO 3 ) 3 and Al(NO 3 ) 3 are acidic salts and do not give up H+ ions as easily. b. Write a chemical reaction for one of these compounds showing how it can lower the pH of water. HNO 3 (g) + H 2 O (l) → H 3 O + (aq) + NO 3 - (aq) 8. Many basic compounds have a hydroxide ion (OH − ) as part of the formula, which becomes dissociated and part of the water solution when the compound is dissolved in water. a. Which of the Module II compounds fit(s) this description? Some of the Module II compounds that fit this description are NaOH, NaC 2 H 3 O 2 , Na 2 CO 3 , and NaHCO 3 . b. Write a chemical reaction for one of these compounds showing how it can raise the pH of water. NaHCO 3 _ (s) + H 2 O (l) → Na + (aq) + HCO 3 - (aq) 9. Some compounds can lower the pH of water even without having a hydrogen in the formula. a. Which of the Module II compound(s) fit(s) this description? NaCl would fit this description.

b. Write a chemical reaction for one of these compounds showing how it can lower the pH of water. ( Hint: You can find a similar example in OpenStax Chemistry 2e section 14.4 ) NaCl (s) + H 2 O (l) → NaOH (aq)+ HCl (aq) 10. Some compounds can raise the pH of water even without having a hydroxide ion in the formula. a. Which of the Module II compound(s) fit(s) this description? #$ ! %& " , #$'%& " , and #$ " (& # b. Write a chemical reaction for one of these compounds explaining how they can raise the pH of water. Na 2 CO 3 (s) + H 2 O -> 2Na(aq) + CO 3 (aq) Module 3 Buffers For the following questions, you can use ‘HA’ to refer to the undissociated acid and ‘A − ’ to refer to the anion of the dissociated acid, i.e. the conjugate base. H + refers to the added acid and OH − refers to the added base. 11. Include a copy of your table of results for both the A wells and the B wells. pH pH pH pH pH Well Predominant Species present initially ( ') , ) $ , ' ! & , ' % , &' $ ) Initial Plus 1 drop acid Plus 2 drops acid Plus 1 drop base Plus 2 drops base A1 ' ! & 6.33 3.04 2.44 ------------- ---------------- A2 ') + ' ! & 2.92 2.90 2.68 -------------- ---------------- A3 ) $ + ' ! & 6.75 5.58 5.25 -------------- ---------------- A4 ') + ) $ 4.60 4.52 4.42 -------------- ---------------- A5 ' % + ' ! & 2.46 2.40 2.30 -------------- ---------------- A6 &' $ + ' ! & 10.6 3.34 2.47 -------------- ---------------- B1 ' ! & 7.90 -------------- -------------- 9.90 11.6 B2 ') + ' ! & 3.20 -------------- -------------- 3.41 4.20 B3 ) $ + ' ! & 6.60 -------------- -------------- 10.9 11.5 B4 ') + ) $ 4.74 -------------- -------------- 4.79 4.91 B5 ' % + ' ! & 2.65 -------------- -------------- 5.50 11.12 B6 &' $ + ' ! & 11.03 -------------- -------------- 11.5 11.65 12. Compare the behaviors of the strong acid (A5 and B5) and strong base (A6 and B6) solutions when small quantities of acid or base are added. Which combinations of solution and added component gave a large change in pH (in either direction) and which gave a smaller change? The pH of well B5 increased in larger increments when extra drops of the base were added while well A5 did not change as dramatically when extra drops of the acid were added. Both wells contained a strong

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acid thus when the base was added to B5, it would react almost completely and raise the pH by a lot more. There was a similar trend with the A6 and B6 wells containing the strong base. The pH of well A6 decreased dramatically when extra drops of acid were added, in contrast to well B6 which did not change as much with added drops of base. The strong base was able to react almost completely when adding more drops of acid which lowered the pH by a lot with each drop. Well A6 ( &' $ + ' ! & + 1 drop acid) had the largest change in pH of +7.26, and Well A2 ( ') + ' ! & + 1 drop acid) had the smallest change in pH of -0.02. 13. Which pair (A and B) of wells containing the same solution best resisted change in pH in both directions – i.e. pair which had the smallest change after adding drops of both acid and base. Wells A4 and B4 contained the same solution and best resisted change in pH in both directions with a change in pH of -0.08 when 1 drop of acid was added, and a change in pH of +0.05 when 1 drop of base was added.