You found a bottle of aqueous solution in the laboratory cabinet. Unfortunately, the label has been eroded and you could not recognize it. To the best of your recollection, it may be one of the following solutions: HCl CH3COOH CH3CH2COOH A mixture of HF and NaF (both of substantial amount) A mixture of H3PO4 and NaH2PO4 (both of substantial amount) NH4Cl NaHCO3 In order to identify the solution, you conduct the following experiments: 1. Using a pH meter, you determine the pH of the solution be 3.00. 2. You dilute 20 mL of the solution with water to a total volume of 200 mL and measure the pH again, this time it reads 3.50. 3. You take some volume of the solution, add phenolphthalein, and titrate it with NaOH solution until the mixture turns pink. You record the volume of the required titrant as Vt and the pH meter reads 9.05. ti =0.0 and tf=2.0. 4. In a separate flask, you take the same volume of the unknown solution as in step iii and titrate it with the same NaOH solution, but this time only adds half of the volume Vt/2. The mixture remains colorless and the pH meter reads 4.87. (A) Identify what’s in the solution and explain your reasoning. Aside from explaining why it is X, you must also explain why it is not A, B, C, etc. (B) The volume of the unknown solution you took in steps iii and iv was 20.00 mL. The concentration of the NaOH solution was 0.04587 M and Vt = 32.98 mL. Calculate the concentration(s) of the unknown species. (C) Suppose you used methyl orange instead of phenolphthalein as the indicator in steps iii and iv. Would you underestimate or overestimate the concentration(s) of the unknown?
You found a bottle of aqueous solution in the laboratory cabinet. Unfortunately, the label has been eroded and you could not recognize it. To the best of your recollection, it may be one of the following solutions: HCl CH3COOH CH3CH2COOH A mixture of HF and NaF (both of substantial amount) A mixture of H3PO4 and NaH2PO4 (both of substantial amount) NH4Cl NaHCO3 In order to identify the solution, you conduct the following experiments: 1. Using a pH meter, you determine the pH of the solution be 3.00. 2. You dilute 20 mL of the solution with water to a total volume of 200 mL and measure the pH again, this time it reads 3.50. 3. You take some volume of the solution, add phenolphthalein, and titrate it with NaOH solution until the mixture turns pink. You record the volume of the required titrant as Vt and the pH meter reads 9.05. ti =0.0 and tf=2.0. 4. In a separate flask, you take the same volume of the unknown solution as in step iii and titrate it with the same NaOH solution, but this time only adds half of the volume Vt/2. The mixture remains colorless and the pH meter reads 4.87. (A) Identify what’s in the solution and explain your reasoning. Aside from explaining why it is X, you must also explain why it is not A, B, C, etc. (B) The volume of the unknown solution you took in steps iii and iv was 20.00 mL. The concentration of the NaOH solution was 0.04587 M and Vt = 32.98 mL. Calculate the concentration(s) of the unknown species. (C) Suppose you used methyl orange instead of phenolphthalein as the indicator in steps iii and iv. Would you underestimate or overestimate the concentration(s) of the unknown?
General Chemistry - Standalone book (MindTap Course List)
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Chapter15: Acids And Bases
Section: Chapter Questions
Problem 15.100QP: A 2.500-g sample of a mixture of sodium carbonate and sodium chloride is dissolved in 25.00 mL of...
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Question
You found a bottle of aqueous solution in the laboratory cabinet. Unfortunately, the label has been eroded and you could not recognize it. To the best of your recollection, it may be one of the following solutions:
- HCl
- CH3COOH
- CH3CH2COOH
- A mixture of HF and NaF (both of substantial amount)
- A mixture of H3PO4 and NaH2PO4 (both of substantial amount)
- NH4Cl
- NaHCO3
In order to identify the solution, you conduct the following experiments:
1. Using a pH meter, you determine the pH of the solution be 3.00.
2. You dilute 20 mL of the solution with water to a total volume of 200 mL and measure the pH again, this time it reads 3.50.
3. You take some volume of the solution, add phenolphthalein, and titrate it with NaOH solution until the mixture turns pink. You record the volume of the required titrant as Vt and the pH meter reads 9.05. ti =0.0 and tf=2.0.
4. In a separate flask, you take the same volume of the unknown solution as in step iii and titrate it with the same NaOH solution, but this time only adds half of the volume Vt/2. The mixture remains colorless and the pH meter reads 4.87.
(A) Identify what’s in the solution and explain your reasoning. Aside from explaining why it is X, you must also explain why it is not A, B, C, etc.
(B) The volume of the unknown solution you took in steps iii and iv was 20.00 mL. The concentration of the NaOH solution was 0.04587 M and Vt = 32.98 mL. Calculate the concentration(s) of the unknown species.
(C) Suppose you used methyl orange instead of phenolphthalein as the indicator in steps iii and iv. Would you underestimate or overestimate the concentration(s) of the unknown?
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