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Online quiz 1 - 1.5 Question 4 Consider a solution of a...

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Online quiz 1. (Correct answers are highlighted) Question 1. Please decide whether the following statement is true or false: A charged atom always reacts similarly to the neutral form of the atom. (Answer: False (B)) Answer Student response (%) Comments True 4.4 The ion always has dramatically different Properties compared to the parent atom. False 95.6 Question 2. Ribulose is a(n) (Answer: ketopentose (D)) Answer Student response (%) Comments ketohexose .4 A carbohydrate with five carbons and a terminal Aldehyde group? Has to be a ketopentose… aldotetrose .4 ketotriose .4 ketopentose 98.9 Question 3. The elemental analysis for glucose is C6H12O6 . What is the elemental analysis for maltose (aka glucosylglucose)? (Answer: C12H22O11 (C)) Answer Student response (%) Comments 2*(C6H12O6) 5.8 It’s two molecules of glucose, but don’t forget to subtract the H20 that is removed when the glycosidic bond is formed. C12H12O12 39 C12H22O11 91 C12H22O12 0 None are correct
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Unformatted text preview: 1.5 Question 4. Consider a solution of a weak acid at a pH equal to its pKa. By how much would the pH change, and in which direction, if we added to this solution enough base to neutralize 10% of the total acid? (Answer: .18 higher (C)) Solution: If the pH is equal to the pKa for the weak acid, the concentration of the basic and the acidic forms of the acid must be equal. Take any amount of the total acid, say 1 eq., in which case the basic form = the acidic form = 0.5 eq. If we add 0.1 eq of base, we will convert the basic form to (0.5 + 0.1) = 0.6 eq; similarly, we must reduce the acidic form to (0.5 – 0.1) = 0.4 eq. The new pH will have changed Answer Student response (%) Comments 0.1, higher 79 0.1, lower 3.6 0.18, higher 14 This is correct. 0.18, lower 1.1 040, higher 1.8 by log(0.6/0.4), which = 0.18 pH unit. And, since we are adding base, the pH must increase....
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