HMWK 7 FA 2015

# HMWK 7 FA 2015 - C211 FALL 2015 HMWK 7 DUE Wednesday...

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C211 FALL 2015 HMWK 7 Name _________________________ DUE Wednesday November 11, BY 5 PM 14 points total 1. A buffer is prepared by partially titrating 500.0 mL of 0.250 M ammonia, NH 3 (K b = 1.75 x 10 5 ) with 1.25 M HCl until a pH of 9.150 is reached. (a) (0.2 pt) Write the balanced chemical equation for the titration reaction, omitting spectator ions. (b) (0.1 pt) Can the NH 4 + conjugate acid be produced without reacting any of the NH 3 reactant? Circle one: yes (explain how, below) no (c) (0.2 pt) Calculate the ratio of NH 3 to NH 4 + required to achieve the target pH. Ratio = (d) (0.1 pt) How many moles of NH 3 are initially present? Amount NH 3 = (e) (0.2 pt) How many moles of the conjugate acid must be produced? How many moles of the strong acid must be added in order to do this? Moles NH 4 + = Moles HCl added = (f) (0.2 pt) What volume of the strong acid will be added to the original solution? What is the final total volume? Volume SA added = Final total Volume =

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(g) (0.2 pt) What are the concentrations of the conjugate acid and base in the final volume of the buffer? Conc. conj. acid = Conc. conj. base = 2. (a) (0.4 pts) Explain in words what the charge balance equation means.
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