If you added 4.5ml of 1.0M HCl to 100ml of 0.10M glycine, pH 12.0, what would be the expected (calculated) pH?Note: Assume that at a pH of 12.0, there are 9.96mmol of the base form (NH2) of glycine in solution. The pKa of basic amine functional group (NH2) in glycine = 9.6 and the pKa of the acidic carboxyl group in glycine (COOH) = 2.3.Selected Answer: [None Given]Answers: A. 10.1B. 2.7C. 9.7D. 4.6E. 9.9
Question
If you added 4.5ml of 1.0M HCl to 100ml of 0.10M glycine, pH 12.0, what would be the expected (calculated) pH?Note: Assume that at a pH of 12.0, there are 9.96mmol of the base form (NH2) of glycine in solution. The pKa of basic amine functional group (NH2) in glycine = 9.6 and the pKa of the acidic carboxyl group in glycine (COOH) = 2.3.Selected Answer: [None Given]Answers: A. 10.1B. 2.7C. 9.7D. 4.6E. 9.9
Solution
To solve this problem, we need to use the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]). In this case, the pKa we are interested in is 9.6, which corresponds to the basic amine functional group (NH2) in glycine.
First, we need to calculate the moles of HCl and glycine. The moles of HCl can be calculated by multiplying the volume (in liters) by the molarity, which gives 4.5ml * 1.0M = 0.0045 moles. The moles of glycine can be calculated similarly, giving 100ml * 0.10M = 0.01 moles.
Next, we need to calculate the moles of the base form of glycine after the addition of HCl. Since HCl is a strong acid, it will react completely with the base form of glycine, converting it to the acid form. This means that the moles of the base form of glycine will decrease by the moles of HCl added, giving 9.96mmol - 0.0045 moles = 9.9555 moles.
Finally, we can substitute these values into the Henderson-Hasselbalch equation to calculate the final pH. This gives pH = 9.6 + log(9.9555/0.0045) = 9.6 + 3.1 = 12.7. However, this value is above the maximum possible pH of 14, so the final pH will be 14.
None of the given answer choices match this calculated pH, so there may be an error in the problem or the answer choices.
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