A metal is known to form fluoride \(M \mathrm{~F}_{2}\). When 10 ampere electricity is passed throwgh i multen salt for \(330 \mathrm{sec}, 1.95 \mathrm{~g}\) metal is deposited. Find out the atomic weight of metal. What will be the quantity of charge required to deposit the same mass of \(\mathrm{Cu}\) from \(\mathrm{CuSO}_{4}\) (aq.) (At. wt. of \(\mathrm{Cu}=63.6\) )

Short Answer

Expert verified
The atomic weight of the metal is calculated using the formula A = (m * F) / Q, after finding the electrochemical equivalent Z. For the same mass of copper, the charge required can be determined from the copper's electrochemical equivalent and Faraday's law.

Step by step solution

01

Identify the Relevant Information

Determine the amount of charge passed and the mass of metal deposited. Here, 10 A of current is passed for 330 s, resulting in the deposition of 1.95 g of the metal.
02

Use Faraday’s First Law of Electrolysis

According to Faraday's First Law, the mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity that passes through the electrolyte. The mass (m) deposited is given by the equation m = (Z * Q) / F, where Z is the electrochemical equivalent of the metal, Q is the quantity of electricity (in coulombs), and F is the Faraday constant (approximately 96500 C/mol).
03

Calculate the Quantity of Electricity Used

The quantity of electricity (Q) in coulombs is given by the product of current (I) in amperes and time (t) in seconds. So, Q = I * t = 10 A * 330 s = 3300 C.
04

Determine the Electrochemical Equivalent (Z)

The electrochemical equivalent Z is the proportionality factor that relates the quantity of electricity to the mass of the substance. Given that 1.95 g of metal is deposited by 3300 C, we can rearrange the equation from Step 2 to find Z: Z = (m * F) / Q = (1.95 g * 96500 C/mol) / 3300 C.
05

Calculate the Atomic Weight of the Metal

Using the valency of the metal (from the given metal fluoride MF2, the valency is 2), we can relate the electrochemical equivalent to the atomic weight (A) of the metal as follows: A = Z * F * valency. After calculating Z, we can substitute it here to find the atomic weight of the metal.
06

Find the Charge Required to Deposit Copper

To find the charge required to deposit the same mass of copper, we need to calculate copper's electrochemical equivalent using its atomic weight and valency (which for copper in CuSO4 is 2). Z_Cu = atomic weight of Cu / (F * valency of Cu). Then, we use the formula Q_Cu = m * F / Z_Cu to find the quantity of charge needed.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electrochemical Equivalent
Understanding the electrochemical equivalent is crucial for solving electrolysis problems. Imagine it as the bridge that connects the electrical world with the chemical world. In technical terms, it is the amount of a substance that is deposited or dissolved at an electrode during electrolysis for every unit of electric charge that passes through the electrolyte.

How do we find it? You would compute it by dividing the mass of the substance deposited by the total charge used in the process, essentially using Faraday's First Law as your formula guide. In our problem, after finding out how much charge was used to deposit metal (calculated by multiplying the current by the time), we can determine the electrochemical equivalent of the metal simply by rearranging the formula from the solution steps. This value is pivotal for calculating the atomic weight of the metal, which is our next step.
Atomic Weight Calculation
The atomic weight of a metal in electrolysis isn't just a number; it's a scale for measuring how much 'stuff' makes up one mole of that metal. When dealing with electrolysis, we're not only interested in the mass of a substance that deposits but also in knowing the amount of that substance on a molecular level.

For our problem, the atomic weight is derived from the electrochemical equivalent, and the electrochemical equivalent is directly proportional to the atomic weight. Once we have the electrochemical equivalent and we know the valency (which is the charge the ion would have in an ionic compound), we can apply both to Faraday’s First Law to find the atomic weight. This figure is indispensable for chemists and physicists alike for calculations involving molecular amounts.
Electrolysis Problems
Facing electrolysis problems can sometimes leave students with more questions than answers. Understanding not just one concept but the interplay between physics and chemistry is the key to solving these problems. Firstly, identify what information is given and what needs to be calculated; in our exercise, we're after the atomic weight and the charge required to deposit a different metal.

Common issues often arise from misinterpreting the relationship between atomic weight and electrochemical equivalent or misunderstanding the valency involved. Precision in applying the correct formulas, as we've done in following Faraday's First Law, saves the day. Clear steps are the roadmap to finding solutions—know what you're solving for, use the right formulas, and pay attention to the units involved. With a well-designed strategy, you'll move from being puzzled by electrolysis to skillfully unraveling its mysteries.
Quantity of Electricity in Electrolysis
In electrolysis, the quantity of electricity refers to the total electric charge that is transferred through the electrolyte, facilitating the chemical change at the electrodes. Recollect that charge is measured in coulombs, and one ampere of current passing for one second equals one coulomb. To frame it simply, it's like measuring the flow of water through a pipe—the quantity of electricity is the total flow of our 'electric water'.

In the given problem, the charge needed to deposit copper is found by using the electrochemical equivalent of copper, which in turn needs the copper's atomic weight and valency. By substituting these values in the appropriate formula, you quantify the electrical charge required to deposit a specific mass of copper. This concept isn't just useful for solving textbook problems, it is essential for any real-world application of electrolysis, such as electroplating or purification of metals.

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Most popular questions from this chapter

$$ \begin{aligned} &\text { The e.m.f. of the cell } M \mid M^{n+}(0.02 M) \| \mathrm{H}^{+}(1 M) \mathrm{H}_{2(\mathrm{~g})}(1 \mathrm{~atm}) \mathrm{Pt} \text { at }\\\ &25^{\circ} \mathrm{C} \text { is } 0.81 \mathrm{~V} \text { . Calculate the valence of metal if } E^{\circ}{ }_{\ldots 1 / 2}^{n+}=0.76 \mathrm{~V} \end{aligned} $$

Write the nernst equation and e.m.f. of the following cells at \(298 \mathrm{~K}\) : (a) \(\mathrm{Mg}(\mathrm{s})\left|\mathrm{Mg}^{2+}(0.001 \mathrm{M}) \| \mathrm{Cu}^{2+}(0.0001 \mathrm{M})\right| \mathrm{Cu}(\mathrm{s})\) (b) \(\mathrm{Fe}(\mathrm{s})\left|\mathrm{Fe}^{2+}(0.001 M) \| \mathrm{H}^{\mathrm{i}}(1 \mathrm{M})\right| \mathrm{H}_{2}(\mathrm{~g})(1 \mathrm{bar}) \mid \mathrm{Pt}(\mathrm{s})\) (c) \(\mathrm{Sn}(\mathrm{s})\left|\mathrm{Sn}^{2+}(0.050 \mathrm{M}) \| \mathrm{H}^{+}(0.020 \mathrm{M})\right| \mathrm{H}_{2}(\mathrm{~g})(1 \mathrm{bar}) \mid \mathrm{Pt}(\mathrm{s})\) (d) \(\mathrm{Pt}(\mathrm{s})\left|\mathrm{Br}_{2}(\mathrm{l})\right| \mathrm{Br}^{-}(0.010 \mathrm{M}) \| \mathrm{H}^{+}(0.030 \mathrm{M}) \mid \mathrm{H}_{2}(\mathrm{~g})(\mathrm{I} \mathrm{bar}) ! \mathrm{Pt}(\mathrm{s})\) Given : \(E_{\text {OP }}^{\circ} \mathrm{Mg}=2.36 \mathrm{~V}, E_{\mathrm{OP}}^{\circ} \mathrm{Cu}=-0.34 \mathrm{~V}, E_{\mathrm{OP}}^{\mathrm{O}} \mathrm{Fe}=0.44 \mathrm{~V}\) \(E_{\mathrm{OP}}^{\circ} \mathrm{Sn}=0.14 \mathrm{~V}\) and \(E_{\mathrm{OP}}^{\circ} \mathrm{Br}_{2}=-1.09 \mathrm{~V}\) respectively.

Given the standard electrode potentials; \(\mathrm{K}^{+} / \mathrm{K}=-2.93 \mathrm{~V}, \quad \mathrm{Ag}^{+} / \mathrm{Ag}=0.80 \mathrm{~V}, \quad \mathrm{Hg}^{2+} / \mathrm{Hg}=0.79 \mathrm{~V}\) \(\mathrm{Mg}^{2+} / \mathrm{Mg}=-2.37 \mathrm{~V}, \quad \mathrm{Cr}^{3+} / \mathrm{Cr}=-0.74 \mathrm{~V}\) Arrange these metals in their increasing order of reducing power.

For the cell : $$ \text { Zn }\left|\begin{array}{c} \mathrm{Zn}_{\text {aq }}^{2+} \\ 1 M \end{array}\right|\left|\begin{array}{c|c} \mathrm{Cu}_{a q}^{2+} \\ 2 M \end{array}\right| \mathrm{Cu} $$ Calculate the values for ; (a) cell reaction, (b) \(E_{\text {cell }}^{\circ}\). (c) \(E_{\text {cell }}\) (d) the minimum concentration of \(\mathrm{Cu}^{2+}\) at which cell reaction is spontaneous if \(\mathrm{Zn}^{2+}\) is \(1 M\) (e) does the displacement of \(\mathrm{Cu}^{2+}\) goes almost to completion. Given : \(E_{R P_{\mathrm{Cu}^{2+} / \mathrm{Cu}}}^{\circ}=+0.35 \mathrm{~V}\) $$ E_{R P_{\mathrm{Zn}^{2+} / Z n}}^{\circ}=-0.76 \mathrm{~V} $$

Calculate the standard cell potentials of galvanic cell in which the following reactions take place : (Given \(E_{\text {OP }}^{\circ} \mathrm{Cr}, \mathrm{Cd}, \mathrm{Fe}^{2+}, \mathrm{Ag}\) are \(0.74 \mathrm{~V}, 0.40 \mathrm{~V},-0.77 \mathrm{~V}\) and \(-0.80 \mathrm{~V}\) respectively) (a) \(2 \mathrm{Cr}_{(\mathrm{s})}+3 \mathrm{Cd}^{2+}\) (aq.) \(\longrightarrow 2 \mathrm{Cr}^{3+}{ }_{\text {(aq. })}^{3+} 3 \mathrm{Cd}\) (b) \(\mathrm{Fe}^{2+}{ }_{\text {(aq.) }}+\mathrm{Ag}_{(\mathrm{aq})}^{+} \longrightarrow \mathrm{Fe}^{3+}{ }_{\text {(aq.) }}+\mathrm{Ag}_{(\mathrm{s})}\) Calculate the \(\Delta_{\mathrm{r}} G^{\circ}\) and equilibrium constant of the reactions.

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