Sample Lab Questions Investigations #20 and #21

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1.

(1 pt) Define end point.

2.

(1 pt) Define heterogeneous mixture.

3.

(1 pt) What is the color of a H₂SO₄ solution?

4.

(1 pt) Give one safety rule for the titrations performed in Investigations #20 or #21.

5.

(2 pts) Balance the folowing hypothetical half-reactions in acid solution:

(a) MnO₄^- Mn⁴⁺

(b) C₂O₄^2- CO₂

6.

Given the following unbalanced equation for a redox reaction: KCN(aq) + KMnO₄(aq) + H₂O(l) MnO₂(s) + KCNO(aq) + KOH(aq)

a. (1pt) Which compound is the oxidizing agent? (2pts) Which element is reduced? What are its oxidation numbers before and after the reaction?

b. (1pt) Balance the reduction half-reaction: MnO₄^- + H₂O + e^- MnO₂ + OH^-

c. (2pts) Give the balanced equation for the total reaction.

d. (2pts) Give the balanced net ionic equation for this reaction.

7.

To determine the percent of sodium oxalate (Na₂C₂O₄) in an unknown sample, a student took 0.5946 g of the unknown sample and dissolved it in 150 mL of water. After adding some H₂SO₄ and MnSO₄, he titrated it with 0.01612 M KMnO₄ solution.

a. (1pt) Balance the equation for the titration reaction: KMnO₄ + Na₂C₂O₄ + H⁺ Mn²⁺ + Na⁺ + K⁺ + CO₂ + H₂O

b. (4pts) Determine the percent of Na₂C₂O₄ in the unknown sample if the titration required 28.33 mL of the KMnO₄ solution.

8.

(2pts) What is the mass of KMnO₄ (in grams) needed to prepare 250mL of a 0.025M solution of KMnO₄?

9.

(3pts) Given the following ionic equation: 2MnO₄^- + 5C₂O₄^2- + 16H⁺ 2Mn²⁺ + 10 CO₂ + 8 H₂O A freshly prepared KMnO₄ solution was standardized by titrating 0.5638 g of sodium oxalate (Na₂C₂O₄) with 40.25 mL of the KMnO₄ solution Calculate the molarity of the KMnO₄ solution.

Answers

6. (a) KMnO₄ (b) Mn +7 +4 7. (b) 25.76% 8. 0.99 g 9. 0.04181 M

To report any corrections, please e-mail Dr. Wendy Keeney-Kennicutt.