When zinc is refined by electrolysis, the desired half-reaction at the cathode is Zn^2+(a q)+2 e

When zinc is refined by electrolysis, the desired...

Key Concepts

Electrolysis

Electrolysis is the process of driving a non-spontaneous chemical reaction using electrical energy. In this method, the movement of electrons at the electrodes induces oxidation and reduction reactions, making it a key concept for understanding processes such as metal refining where different reactions compete at the electrodes.

Faraday's Laws of Electrolysis

Faraday's laws establish that the amount of chemical change produced at an electrode during electrolysis is directly proportional to the total charge passed through the system. This concept allows the conversion of electrical charge into the amount (in moles) of substance produced or consumed in an electrochemical reaction.

Stoichiometry of Electrode Reactions

Stoichiometry in electrode reactions involves using the balanced chemical equations to relate the number of electrons transferred to the number of moles of substances produced or consumed. This direct proportionality is essential for quantifying how much product is formed per unit of electrical charge in a reaction.

Current Efficiency

Current efficiency, sometimes called the Faradaic efficiency, is the percentage of the total current that is used effectively in producing the desired chemical transformation. This concept is crucial when some part of the current is diverted to side reactions, affecting the overall yield of the target substance.

Gas Volume at Standard Temperature and Pressure (STP)

Understanding the gas volume at STP is important for converting the moles of a gaseous product, calculated via stoichiometry, into liters. At STP, the ideal gas law provides a standard basis—where one mole of an ideal gas occupies 22.4 liters—which is widely used for practical measurements in gas evolution reactions.

Transcript

00:01 Question number 140 is an equilibrium problem involving ksp of the insoluble compound mercury 1 chloride.

00:11 In addition, there are some unique conversions that are involved in this problem.

00:16 The first thing they want you to do is identify the empirical formula for mercury 1 chloride.

00:22 Mercury 1 is a diatomic ion that is hg22.

00:25 So if hg222 plus is the cation, and chloride just has a 1 -minus charge, then we will need two chlorides for every 1 hg2 .2 .2 .2.

00:38 Then for part b, it wants you to calculate the concentration of the hg2, 2 ,2, plus, in a saturated solution of mercury chloride.

00:47 To do that, we need to recognize what the equilibrium is for the ksp process.

00:52 When this dissolves, we'll get 1 mole of mercury and 2 moles of chloride, so ksp will be equal to the concentration of the mercury 1, multiplied by the chloride concentration squared.

01:05 If the only source of chloride and mercury 2 comes from this equilibrium process, then according to the stoichiometry, the chloride concentration will be equal to two times the mercury 2 -2 -plus concentration.

01:18 So i can then plug back into my ksp expression.

01:22 Ksp was given to us at 1 .5 times 10 to the negative 18.

01:26 That will then be equal to the mercury 2 -2 -plus concentration multiplied by the chloride concentration squared, which is two times the mercury 2 -2 plus concentration, and then don't forget to square it.

01:39 So now i have one equation and one unknown, and i can solve for the mercury 2 -2 plus concentration.

01:45 It'll be the cube root of ksp, 1 .5 times 10 to the negative 14, divided by 4, because when i square this, i'm going to square that 2 and make it 4.

01:56 That gives me a concentration of 7 .21 times 10 to the negative 0 .4.

02:02 Now for part c, it tells us that sea water contains 0 .2 pounds of sodium chloride per gallon.

02:11 We can use this information to solve for the chloride concentration, and then knowing the chloride concentration and this equation up here, we can solve for the mercury concentration.

02:22 But concentrations need to be in units of malarity in order to use the ksp expression up here.

02:29 So we'll convert the pounds into gram.

02:31 To do that, we recognize that for every pound there's 453 .59 grams.

02:39 This is now the mass of sodium chloride per gallon of seawater.

02:42 We'll then convert the gram sodium chloride into mole's sodium chloride, recognizing the molar mass of sodium chloride is 58 .44 grams per mole...

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