3.2 - Redox Stoichiometry
Module 5
Lesson 3.2 Redox Stoichiometry
Key Concepts
Titration analysis is not simply used to analyze acid/base systems. This important laboratory method can also be applied to redox systems. Watch the following two instructional videos to learn how to do the stoichiometric calculations for redox titrations.
Watch
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Learning Tip When a titration is used to analyze the unknown concentration of a sample, the concentration of the titrant must be known precisely. Sometimes the concentration of the titrant is provided. Sometimes, however, the precise concentration of the titrant must be determined prior to titrating a sample of unknown concentration. For example, later in this lesson, you will be using potassium permanganate to find the exact concentration of a hydrogen peroxide solution. However, before the hydrogen peroxide can be titrated, the exact concentration of the potassium permanganate solution must be determined. To do this, the potassium permanganate is used to titrate a known volume of a primary standard. Because the exact concentration of the primary standard is known, we can determine the precise concentration of the potassium permanganate. |
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Check Your Understanding
Complete Practice Questions 3 and 5 on page 598 of the textbook. Click on the link below to check your work.
\( \mathrm { Ni(s) \rightarrow Ni^{2+}(aq) + 2e^- } \)
\( \mathrm { (Ag^+(aq) + 1e^- \rightarrow Ag(s)) \times 2 } \)
\( \mathrm { Ni(s) + 2 Ag^+(aq) \rightarrow Ni^{2+}(aq) + 2 Ag(s) } \)
\( \mathrm { mol~ Ni(s) = \dfrac{m}{M} = \dfrac{25.0 g}{58.69 \frac{g}{mol}} = 0.426 mol } \)
\( \mathrm { mol~ Ag^+(aq) = 0.426 ~mol \times 2/1 = 0.852~ mol } \)
\( \mathrm { volume~Ag^+(aq) = \dfrac{n}{c} = \dfrac{0.852~mol}{0.10 \frac{mol}{L}} = 8.5 L } \)
The volume of 0.10 mol/L silver ion solution that will react is 8.5 L.
Page 598 Practice Question 5
First, calculate the concentration of the Fe2+ primary standard solution:
\( \mathrm { mol~ Fe^{2+} = mol~ Fe = \dfrac{m}{M} = \dfrac{1.08~ g}{ 55.85~\frac{g}{mol}} = 0.0193~ mol } \)
\( \mathrm { [Fe^{2+}(aq)] = \dfrac{n}{V} = \dfrac{0.0193~ mol}{0.2500~ L} = 0.0774~ \frac{mol}{L } } \)
Next, calculate the concentration of the potassium permanganate solution.
\( \mathrm { (Fe^{2+}(aq) \rightarrow Fe^{3+}(aq) + 1e^-) \times 5 } \)
\( \mathrm { MnO_4^-(aq) + 8 H^+(aq) + 5e^- \rightarrow Mn^{2+}(aq) + 4 H_2O(l) } \)
\( \mathrm { 5 Fe^{2+}(aq) + MnO_4^-(aq) + 8 H^+(aq) \rightarrow 5 Fe^{3+}(aq) + Mn^{2+}(aq) + 4 H_2O(l) } \)
\( \mathrm { mol~ Fe^{2+}(aq) = cV = {0.0774~ \frac{mol}{L}} \times {0.0100~ L} = 0.000 774~ mol } \)
\( \mathrm { mol~ MnO_4^-(aq) = 0.000 774~ mol \times 1/5 = 0.000 155~ mol } \)
\( \mathrm { [MnO_4^-(aq)] = \dfrac{n}{V} = \dfrac{0.000 155~ mol}{ 0.0136~ L} = 0.0114~\frac{mol}{L} } \)
The concentration of the permanganate solution is 0.0114 mol/L.
Virtual Investigation
- Open the virtual investigation by clicking on the graphic to the right.
- For this virtual investigation select Redox Titration, Exercise 1.
- Work through Procedures 1 and 2.
- Record all data in your Module 5 Summative Assessment.
- Answer all associated questions in your Module 5 Summative Assessment.
