Chemistry 111 Fall 2004. Practice for Second In-class Exam.

Read everything before doing anything. Answer all the questions in any order you like. Partial credit is available for some questions. Merit (5 points) is attached to clarity of presentation. Note that not all the questions carry the same number of points.

1. A 25.00-mL sample of vinegar requires 28.33 mL of 0.953 M solution of potassium hydroxide for titration to the equivalence point. What is the concentration of acetic acid in the vinegar in g per 100 mL? (20 points)

2. Balance the following expression (5 points).

__K₃PO₄ + _Ca(NO₃)₂ ==> __KNO₃ + _ Ca₃(PO₄)₂

3. Write the net ionic equation for the reaction, if any, which occurs when manganese(II) carbonate, which is insoluble, and hydrochloric acid solution are mixed. (5 points). Manganese chloride is soluble and hydrochloric acid is a strong acid.

4. Write the net ionic equation for the reaction between potassium hydroxide (a strong base) and acetic acid (a weak acid) in aqueous solution. (5 points) Potassium acetate is soluble.

5. Balance the equation for the reaction between permanganate and bromide in acid solution to give bromine and manganese(II) ions: (5 points)

MnO₄^- + Br^- + H⁺ ==> Br₂ + Mn²⁺ + H₂O

6. Is the reaction between zinc metal and hydrochloric acid solution, to form zinc(II) ions, chloride ions and hydrogen gas, a redox reaction? (5 points) If so, what is the oxidizing agent and what is the reducing agent? (5 points)

7. Propane (C₃H₈) burns in oxygen to form carbon dioxide and water. An unknown mass of propane was burned and all the carbon dioxide formed from the reaction was passed through an aqueous solution of barium hydroxide. Carbon dioxide reacts with barium hydroxide to give insoluble barium carbonate, and 0.253 g of barium carbonate precipitated. What mass of propane was burned? The molar mass of barium carbonate is 197.334 and the molar mass of propane is 44.097. (20 points)

8. What are the names of the following compounds: Fe(NO₃)₃, CdSO₄, CaCO₃, AlPO₄, CH₃COONH₄? (5 points)

9. Element X combines with oxygen to form a compound with the formula X₂O₃. If 0.0320 g of oxygen combines with 0.163 g of X, calculate the atomic weight of X (10 points)

10. Succinic acid, which contains only the elements carbon, oxygen and hydrogen, and has molecular weight of 118 g mol^-1. Suggest a plausible molecular formula for succinic acid? (5 points)

11. What is the concentration of magnesium (in g/L) in a solution made by dissolving 10.0 g of magnesium metal in hydrochloric acid solution and making up to 250.0 mL? (5 points). If 20.0 mL of this solution is diluted to 100.0 mL, what is the concentration of the final solution in g/L? (5 points)

Possible useful information. Atomic weights: C 12.0, H 1.01, and O 16.0. Avogadro’s number 6.02 x 10²³. Vinegar is a mixture of acetic acid and water.