Question

Consider the reaction:
${\text{C}}{{\text{r}}_2}{\text{O}}_7^{2 - } + 14{{\text{H}}^ + } + 6{{\text{e}}^ - } \to 2{\text{C}}{{\text{r}}^{3 + }} + 7{{\text{H}}_2}{\text{O}}$
What is the quantity of electricity in coulombs needed to reduced 1 mol of ${\text{C}}{{\text{r}}_2}{\text{O}}_7^{2 - }?$
A.$6 \times {10^6}{\text{C}}$
B.$5.79 \times {10^5}{\text{C}}$
C.$5.25 \times {10^5}{\text{C}}$
D.None of these

Answer 1

Hint: The chromate anion is found in chromate salts. The dichromate anion is found in dichromate salts. They are relatively potent oxidising agents that are chromium oxyanions in the + 6 oxidation state. The chromate and dichromate ions will interconvert in an aqueous solution.

Complete answer:
In chemistry, an element's valence or valency is a measure of its ability to combine with other atoms to form chemical compounds or molecules.
The valency factor, also known as the conversion factor, is the 'n' factor. The number of moles of lost or gained electrons per molecule is proportional to the n – factor of material in a redox reaction. * In a non-redox reaction, the n – component of material equals the product of the displaced mole and its charge.
The oxidation state of the chromate ion is shifting from +6 to +3. To put it another way, this reaction entails the transfer of six electrons, so the n component is six.
The chemical deposition caused by current flow through an electrolyte is directly proportional to the amount of electricity (coulombs) passing through it, according to Faraday's First Law of Electrolysis. Where Z is the electro-chemical equivalent of the product and is a proportionality constant.
$m \propto Q$
${\text{C}}{{\text{r}}_2}{\text{O}}_7^{2 - } + 14{{\text{H}}^ + } + 6{{\text{e}}^ - } \to 2{\text{C}}{{\text{r}}^{3 + }} + 7{{\text{H}}_2}{\text{O}}$
Using Faraday first law of electrolysis we have
$\dfrac{{\text{Q}}}{{\text{F}}} = {\text{mole}} \times {\text{Valency factor}}{\text{. }}$
${\mathbf{Q}} = {\text{ mole }} \times {\mathbf{V}}{\text{ }}{\text{.f}}{\text{. }} \times {\mathbf{F}}$
Where F = Farad
Upon substituting we get
Q = 1 x 6 x 96500
Q = $5.79 \times {10^5}{\text{C}}$
Hence option B is correct.

Note:
The energy emitted or consumed by a body or a thermodynamic system during a constant-temperature process — typically a first-order step transition — is known as latent heat (also known as latent energy or heat of transformation).
Latent heat is energy that is supplied or absorbed in a secret way to change the state of a material without changing its temperature. Phase transitions, such as a material condensing or vaporising at a given temperature and pressure, are examples of latent heat of fusion and latent heat of evaporation.