CHEM 120 Reactions in Aqueous Solutions - Full Solutions

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Note: M is the symbol for the unit mol/L.

1. Select the best and poorest electrical conductors from the following solutions.
(a)
Best
0.95 M NH3
0.95 M LiI
0.95 M HClO (hypochlorous acid)
0.95 M HOCH2CH2OH (ethylene glycol)
Answer: 0.95 M LiI

(b)
Poorest
0.95 M NH3
0.95 M LiI
0.95 M HClO (hypochlorous acid)
0.95 M HOCH2CH2OH (ethylene glycol)(a)
Answer: 0.95 M HOCH2CH2OH (ethylene glycol)


2. Which solution has the greatest [SO4(2−)]?
Answer: 0.32 M Cr2(SO4)3


3. If one assumes the volumes are additive, what is the concentration, in mol/L, of NO(3−) in a solution obtained by mixing 285 mL of 0.285 M KNO3, 329 mL of 0.473 M Mg(NO3)2, and 715 mL of H2O?
Enter your answer in mol/L
Answer: 0.178


4. How many milliliters of 0.0861 M Ba(OH)2(aq) are required to titrate 55.00 mL of 0.0461 M HNO3(aq)?
Answer: 14.8 mL



5. When aqueous potassium phosphate, K3PO4, is treated with an excess of concentrated nitric acid solution, HNO3(aq), the products are potassium nitrate, KNO3, and phosphoric acid, H3PO4. What is the net ionic equation for this reaction?
Answer: PO4(3-)(aq) + 3 H(+)(aq) ---> H3PO4 (aq)


6. What is the average oxidation number (i.e. oxidation state) of Xe in XeOF2?
Answer: 4


7. Complete and balance the following chemical equation using the smallest whole number coefficients. Assume the reaction takes place in acidic aqueous solution. Use H+ to balance charge, not H3O+.
Cr2O7(2-) + Fe(2+)  -->  Cr(3+) + Fe(3+) (acidic solution)
Answer:   Cr2O7(2-) + 6Fe(2+) + 14H(+)  -->  2Cr(3+) + 6Fe(3+) 7H2O


8. Complete and balance the equation for the following oxidation-reduction reaction using the smallest whole number coefficients. The reaction occurs in aqueous basic solution.
CrO4(2-) + Ag → Ag(+) + Cr(OH)3
Answer:  CrO4(2-) + 3Ag + 4H2O→ 3Ag(+) + Cr(OH)3 + H + 5OH(-)