Worksheet 08 Key

# Worksheet 08 Key - CH 302 Spring 2007 Worksheet 8 Answer...

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CH 302 Spring 2007 Worksheet 8 Answer Key 1. NaH 2 PO4 (conc. = C NaH2PO4 ) is dissolved in water. Write the mass balance equation for this system. Answer: C NaH2PO4 = [H 3 PO 4 ] + [H 2 PO 4 - ] + [HPO 4 2- ] + [PO 4 3- ] 2. Write the charge balance equation for the solution in question 1. Answer: [H + ] = [OH - ] + [H 2 PO 4 - ] + 2[HPO 4 2- ] + 3[PO 4 3- ] 3. Write the charge balance equation for a solution containing all of the following ions: H + , OH - , Na + , Ba 2+ , PO 4 3- , Ag 3+ , SO 4 2- , and COOH - . Answer: [H + ] + [Na + ] + 2[Ba 2+ ] + 3[Ag 3+ ] = [OH - ] + [COOH - ] + 2[SO 4 2- ] + 3[PO 4 3- ] 4. NaH 2 PO 4 , LiHCO 3 , HCl, NaCl, and LiOH are all dissolved in water. How many equations are needed to completely describe this system? Answer: In solution, we have: H + , OH - , Na + , H 3 PO 4 , H 2 PO 4 - , HPO 4 2- , PO 4 3- , Li + , H 2 CO 3 , HCO 3 - , CO 3 2- , and Cl - . So we need 12 equations. 5. Write a charge balance equation for the system described in question 4. Answer: [H + ] + [Na + ] + [Li + ] = [OH - ] [Cl - ] + [H 2 PO 4 - ] + 2[HPO 4 2- ] + 3[PO 4 3- ] + [HCO 3 - ] + 2[CO 3 2- ] 6. Write the mass balance equation for H 2 CO 3 (conc. = C H2CO3 ) in water. Answer: C H2CO3 = [H 2 CO 3 ] + [HCO 3 - ] + [CO 3 2- ] 7. Find the pH of 10 -8 M HCl like you would have for the last two quizzes. Then find it using the exact expression, [H + ] 2 – [H + ]C HCl – K w = 0. Compare the two answers.

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