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Question 1

Balance the following equations in acidic conditions:

1. As₂O₃+ NO₃^– à H₃AsO₄ + N₂O₃
2. MnO₄^– + S₂O₃^2– à Mn²⁺+ SO₄^2–
3. H₂O₂+ Cr₂O₇²¯ àCr³⁺ + O₂ + H₂O
4. IO₃^– + SO₂ à I₂ + SO₄^2–
5. Cr₂O₇^2– + Mn²⁺à Cr²⁺ + MnO₄^–
6. H₃PO₂+ Cr₂O₇^2– à H₃PO₄ + Cr³⁺
7. As + ClO₃^– à H₃AsO₃ + HClO

Question 2

Balance the following equations in basic conditions:

1. MnO₄^– + SO₃^2– à MnO₂+ SO₄^2-
2. HPO₃^2– + N₂H₄à H₂PO₂^– + N₂
3. Cr + CrO₄^2– à Cr(OH)₃
4. CrO₄²¯ + S₂O₄²¯ à Cr(OH)₃ + SO₄^2–
5. CN^– + MnO₄^– à CNO^– + MnO₂
6. MnO₂+ O₂ à MnO₄^– + H₂O
7. MnO₄^– + C₂O₄^2– à CO₂+ MnO₂

Question 3

0.2640 g of sodium oxalate is dissolved in a flask and requires 30.74 mL of potassium permanganate (from a buret) to titrate it and cause it to turn pink (the end point).

The equation for this reaction is:

5Na₂C₂O₄ + 2KMnO₄ + 8H₂SO₄ à 2MnSO₄ + K₂SO₄ + 5Na₂SO₄ + 10CO₂ + 8H₂O

1. How many moles of sodium oxalate are present in the flask?
2. How many moles of potassium permanganate have been titrated into the flask to reach the end point?
3. What is the molarity of the potassium permanganate?

Question 4

Potassium dichromate is used to titrate a sample containing an unknown percentage of iron. The sample is dissolved in H₃PO₄/H₂SO₄ mixture to reduce all of the iron to Fe²⁺ ions. The solution is then titrated with 0.01625 M K₂Cr₂O₇, producing Fe³⁺ and Cr³⁺ ions in acidic solution. The titration requires 32.26 mL of K₂Cr₂O₇ for 1.2765 g of the sample.

1. Balance the net ionic equation using the half-reaction method.
2. Determine the percent iron in the sample.
3. Is the sample ferrous iodate, ferrous phosphate, or ferrous acetate?

Question 5

The quantity of antimony in a sample can be determined by an oxidation-reduction titration with an oxidizing agent. A 9.62 g sample of stibnite, an ore of antimony, is dissolved in hot, concentrated HCl and passed over a reducing agent so that all the antimony is in the form Sb³⁺. The Sb³⁺ is completely oxidized by 43.70 mL of a 0.1250 M solution of KBrO₃. Calculate the amount of antimony in the sample and its percentage in the ore.

Question 6

The amount of I₃^– in a solution can be determined by titration with a solution containing a known concentration of S₂O₃²– (thiosulfate ion). The determination is based on the balanced equation:

I₃^– + 2S₂O₃^2– à 3I^– + S₄O₆^2–

Given that it requires 36.40 mL of 0.3300 M Na₂S₂O₃ to titrate the I₃^– in a 15.00 mL sample, calculate the molarity of I₃^– in the solution.

Question 7

A solution of I₃^–(aq) can be standardized by using it to titrate As₄O₆(aq). The titration of 0.1021 g of As₄O₆(s) dissolved in 30.00 mL of water requires 36.55 mL of I₃^–. Calculate the molarity of the I₃^– solution. The unbalanced equation is

As₄O₆ + I₃^– —> As₄O₁₀ + I^–