Redox Chemistry and Titrations Flashcards

Flashcards covering the fundamentals of redox chemistry, oxidation numbers, construction of half-equations, and specific redox titration procedures including iron(II)/manganate(VII) and iodine/thiosulfate systems.

How is an oxidising agent defined in terms of oxidation number?

An oxidising agent is a chemical species, or reactant, which increases the oxidation number of the other species or substance.

How is a reducing agent defined in terms of oxidation number?

A reducing agent is a chemical species, or reactant, which decreases the oxidation number of the other species or substance.

Define oxidation state.

The oxidation state of an ion is the number of electrons that must either be added or removed from that ion in order to give a neutral atom.

What is the oxidation number of an uncombined element?

$$0$$

What is the oxidation number rule for fluorine atoms in compounds?

A fluorine atom is always $-1$.

What are the common oxidation numbers for Group 1, Group 2, and Group 3 metals?

Group 1 metals are always $+1$, Group 2 metals are always $+2$, and Group 3 metals are always $+3$.

What is the formula and oxidation state of the central atom for the Manganate (VII) oxyanion?

$MnO_4^-$ with the manganese in a $+7$ oxidation state.

What is the chemical formula for the thiosulfate ion?

$$S_2O_3^{2-}$$

What is the chemical formula for the dichromate (VI) ion?

$$Cr_2O_7^{2-}$$

What are the two items added liberally when using Method 1 or Method 2 to balance the $O$ and $H$ atoms in oxyanion half equations?

$H_2O$ and $H^+$

Provide the balanced half equation for the reduction of manganate (VII) ions to manganese (II) ions in acid solution.

$$MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O$$

In a redox equation, on which side are the electrons located for an oxidation half equation?

The right-hand side (RHS).

How do you ensure changes in oxidation number are balanced when constructing an equation without using half-equations?

The total increase in oxidation number must equal the total decrease in oxidation number.

What is the reacting ratio of $Fe^{2+}$ to $MnO_4^-$ in the balanced equation for the oxidation of iron (II) by manganate?

$$5:1$$

What is the overall balanced equation for the reaction of copper (II) ions with iodide ions?

$$2Cu^{2+}(aq) + 4I^-(aq) \rightarrow 2CuI(s) + I_2(aq)$$

What is the balanced equation for the titration of iodine with sodium thiosulfate?

$$I_2(aq) + 2S_2O_3^{2-}(aq) \rightarrow S_4O_6^{2-}(aq) + 2I^-(aq)$$

What is the observed end point when adding manganate (VII) to iron (II)?

A pale permanent pink color.

Why is starch solution added during an $I_2/S_2O_3^{2-}$ titration?

Starch is added when the iodine color becomes a pale straw color because the iodine makes the starch go blue-black, making the transition to colorless at the end point more distinct.

In the analysis of brass, what reagents are used to first form a solution of copper ions and then to produce iodine for titration?

Concentrated nitric acid is used to dissolve the brass, and excess aqueous potassium iodide ($KI$) is added to react with the copper (II) ions.

According to the general procedure for a redox titration, how many concordant titres should be averaged?

The procedure specifies repeating the experiment until concordant titres are obtained and then averaging them.