Redox Titrations and Fundamentals

Comprehensive fill-in-the-blank practice flashcards covering oxidation-reduction fundamentals, Nernst equation calculations, oxidation potentials, indicators, and analytical redox titrations.

Oxidation-reduction reactions (Redox) are defined as reactions that involve __________ simultaneously.

oxidation and reduction

According to the classical definition, oxidation refers to combination with oxygen or loss of __________.

hydrogen

According to the classical definition, reduction refers to combination with hydrogen or loss of __________.

oxygen

Under modern definitions, oxidation is defined as the loss of electrons, which leads to an increasing __________ charge or decreasing negative charge.

positive

Under modern definitions, reduction is defined as the gain of electrons, which leads to a decreasing positive charge or increasing __________ charge.

negative

An oxidizing agent (oxidant) gains electrons during a redox reaction and is consequently __________.

reduced

A reducing agent (reductant) donates electrons during a redox reaction and is consequently __________.

oxidized

According to the conjugate relationship of redox systems, the stronger the oxidant, the __________ its conjugated reductant.

weaker

Because free electrons cannot exist in solution, the number of electrons gained by the oxidant must equal the number of electrons __________ by the reductant.

lost

In classical chemistry, equivalent weight was defined as the weight of substance that reacts with or contains $1.008\,g$ of available hydrogen or __________ of available oxygen.

$$8.000\,g$$

Modernly, the equivalent weight of a substance in a redox reaction is calculated as its molecular weight divided by the __________, which represents the number of electrons gained or lost.

n-factor

In an acidic medium, the equivalent weight of $KMnO_4$ equals molecular weight divided by 5 because manganese changes its oxidation state from $Mn^{7+}$ to __________.

$$Mn^{2+}$$

In moderately alkaline conditions where $KMnO_4$ is reduced to $MnO_2$, its equivalent weight equals molecular weight divided by __________.

$$3$$

The equivalent weight of $K_2Cr_2O_7$ is equal to molecular weight divided by __________ because the two chromium atoms together gain a total of 6 electrons.

$$6$$

When an inert electrode such as platinum is immersed in a solution containing a redox system, an EMF is developed which is called the __________.

oxidation potential

Oxidation potential cannot be measured directly and is determined relative to the Normal Hydrogen Electrode (NHE), which has an assigned standard potential of __________.

$$0\,V$$

In any spontaneous redox reaction, electron transfer proceeds from the system with more negative potential to the system with more __________ potential.

positive

According to the Nernst equation at $25^\circ C$, the potential is calculated as $E_{25} = E^\circ + \left(\frac{0.0591}{n}\right) \log\left(\frac{[Ox]}{[Red]}\right)$, where $n$ denotes the __________.

number of electrons

The standard oxidation potential ($E^\circ$) represents the electromotive force established when the oxidant and reductant concentrations are __________.

equimolar

Metals such as $Zn$, $Fe$, $Co$, and $Ni$ that have a strong tendency to lose electrons and dissolve as cations exhibit high __________.

solution pressure

Metal ions such as $Cu^{2+}$, $Hg^{2+}$, and $Ag^+$ that readily gain electrons and deposit as neutral metal atoms exhibit high __________.

ionic pressure

According to the displacement rule, a metal system $M/M^{n+}$ with a negative standard potential will displace the metal ion of a system that has a __________ standard potential.

positive

For non-metal redox systems, a system possessing a more positive potential will displace a non-metal system with a __________ positive potential.

less

For a redox reaction between two systems to proceed quantitatively, the difference in standard oxidation potentials should be at least __________.

$$0.4\,V$$

If the difference between the standard oxidation potentials of two reacting redox systems is less than $0.4\,V$, the reaction is considered __________.

reversible

In the titration of $Fe^{2+}$ with $KMnO_4$ in hydrochloric acid media, __________ is added to prevent interference from chloride oxidation.

Zimmermann's reagent

In Zimmermann's reagent, the component responsible for reducing the oxidation potential of the $MnO_4^- / Mn^{2+}$ system via the common ion effect is __________.

$$MnSO_4$$

In Zimmermann's reagent, $H_3PO_4$ decreases the oxidation potential of the $Fe^{3+} / Fe^{2+}$ system by forming the stable complex __________.

$$[Fe(PO_4)_2]^{3-}$$

In the reversible oxidation of $Fe^{2+}$ by $I_2$, adding $HgCl_2$ lowers iodide concentration and drives the reaction forward by complexing iodide into __________.

$$[HgI_4]^{2-}$$

Adding fluoride ($F^-$) or phosphate ($PO_4^{3-}$) decreases the oxidation potential of the iron couple because these anions form stable complexes selectively with __________.

$$Fe^{3+}$$

For oxygen-containing oxidizing agents such as $KMnO_4$ and $K_2Cr_2O_7$, increasing the acidity leads to a(n) __________ in the oxidation potential.

increase

In a strongly alkaline medium, $KMnO_4$ is reduced to the green manganate ion having the formula __________.

$$MnO_4^{2-}$$

To drive the reversible reaction between $AsO_4^{3-}/AsO_3^{3-}$ and $I_2/I^-$ forward by increasing acidity, concentrated __________ is added because $HNO_3$ and $H_2SO_4$ oxidize iodide.

$$HCl$$

In the titration of $100\,mL$ of $0.1\,N\,FeSO_4$ with $0.1\,N\,Ce(SO_4)_2$, the potential at the equivalence point equals the average of the two standard potentials, which is __________.

$$1.10\,V$$

On a redox titration curve, the sharp, sudden change in potential occurring at the equivalence point is called the __________.

inflection

$KMnO_4$ serves as its own indicator in titrations because one drop of excess solution produces a distinct permanent __________ color.

pink

When determining the endpoint of $Fe^{2+}$ titration with dichromate using external ferricyanide ($[Fe(CN)_6]^{3-}$), unoxidized $Fe^{2+}$ produces a __________ precipitate.

blue

A critical requirement for an internal redox indicator is that its transition potential range must be __________ between the potentials of the analyte and titrant systems.

intermediate

Diphenylamine has a standard transition potential of $E^\circ = 0.76\,V$ and changes from colorless in its reduced form to __________ in its oxidized form.

blue-violet

N-Phenylanthranilic acid ($E^\circ = 1.08\,V$) can be used for the titration of $Fe^{2+}$ with dichromate without adding phosphate or fluoride because its standard potential is already __________.

intermediate

The internal indicator Ferroin consists of a $1,10$-phenanthroline complex with iron(II) that is intense red, which upon oxidation forms Ferrin with a distinct __________ color.

pale blue

When stannous chloride ($SnCl_2$) is used as a pre-reductant for $Fe^{3+}$, the excess $SnCl_2$ is removed prior to titration by adding __________ to precipitate silky white $Hg_2Cl_2$.

$$HgCl_2$$

When granular zinc is employed as a pre-reductant to reduce $Fe^{3+}$ to $Fe^{2+}$, unreacted excess zinc metal is removed by __________ through glass wool.

filtration

When hydrogen peroxide ($H_2O_2$) is utilized as a pre-oxidant, its unreacted excess is removed prior to titration by __________.

boiling in acid medium

During the preparation of standard $KMnO_4$ solution, the dissolved solution is boiled gently for __________ to coagulate and decompose organic impurities.

$$15 - 30\text{ minutes}$$

In the standardization of $KMnO_4$ with sodium oxalate at $70^\circ C$, the initial slow reaction rate increases noticeably because the produced $Mn^{2+}$ acts as an __________.

autocatalyst

The Jones reductor is an analytical column packed with __________ used to quantitatively reduce acidic ferric iron ($Fe^{3+}$) solutions to ferrous iron ($Fe^{2+}$).

amalgamated zinc

During the reduction of $Fe^{3+}$ with $Zn$ and $H_2SO_4$, the titration flask is equipped with a __________ to prevent atmospheric reoxidation of $Fe^{2+}$ to $Fe^{3+}$.

Bunsen valve

By definition, a commercial '100-volume' hydrogen peroxide solution produces __________ of oxygen gas ($O_2$) at STP from every $1\,mL$ of solution.

$$100\,mL$$

Potassium dichromate ($K_2Cr_2O_7$) can be prepared by direct weighing and dissolves stably without standardization, classifying it as a(n) __________.

primary standard