chapter10.3

Question 1

driving non-spontaneous reactions

Answer 1

• redox reactions and spontenaous redox reactions release energy.
• galvanic cells turn energy into electrical energy.

Question 2

electrolytic cells

Answer 2

• cells that use external soruces of electrical energy to drive non-spontaneous redox reactions are called electrolytic cells.
• they can also be described as cells that turn electrical energy into chemical energy.

Question 3

electrolysis

Answer 3

• a process that takes place in an electrolytic cell is called electrolysis
• some galvanic cells can be turned into electrolytic cells, a Daniell cell can be converted by adding a power source.

Question 4

the process of converting a daniell cell into a electrolytic cell

Answer 4

• the power pulls electrons from the copper electrode, oxidizing copper atoms in the electrode to copper(II) ions that go into solution.
• the copper electrode is therefore the anode, because oxidation half-reactions occur there.
• along with that, the power supply is forcing electrons onto the zinc electrode, causing zinc ions in the solution to become reduced to zinc atoms that become part of the zinc elecctrode.

Question 5

the chart on the galvanic cell and daniell cell

Answer 5

• since zinc ions are becoming reduced at the zinc electrode, that electrode is the cathode.
• the entire system is operated opposite to the Daniell cell.

Question 6

calculating the standard cell potential.

Answer 6

• if you calculate the standard cell potential of the redox reactions between zinc atoms and copper ions, it will be +1.0V, if you calculate the standard cell potential of the reverse reaction you will get -1.10V.
• the negative sign means the reaction is not spontaneous, it represents the minimum potential difference that you would have to apply from the external power source to drive the cell reaction for the electrolytic cell.

Question 7

electrolysis in aqueous solutions

Answer 7

• sometimes when you convert galvanic cells to eletrolytic cells the reaction is the reverse of the galvanic cell.
• it depends on the nature of electrolyte dissolved in the aqueous solution, the reverse reaction might not be the reverse of the one that would occur in the galvanic cell.

Question 8

larger galvanic cells

Answer 8

• After volta, sir humphry davy made a larger galvanic cell for electrolysis experiments.
  → he wanted to reduce the metal ions in salts to produce the pure metals. Only a few pure metals had been discovered at this time.

Question 9

how did davy make it work

Answer 9

• He first did electrolysis on salts such as sodium chloride and potassium chloride in aqueous solutions.
• Chlorine gas formed at the anode, hydrogen gas formed at the cathode.
• The only source of hydrogen in the cell was the water in which the sodium chloride was dissolved.
• Water was reduced at the cathode rather than sodium ions.

Question 10

electrolysis of water

Answer 10

• When water goes through electrolysis, some of the water molecules are oxidized at the anode and some are reduced at the cathode.
• Oxygen gas is generated at the anode and hydrogen gas is generated at the cathode, to prevent them from mixing, they are usually placed below or in the closed end of the glass tubes.

Question 11

factors that affect the electrolysis of water

Answer 11

• Factors that affect the electrolysis of water must be considered when doing it, making predictions about reactions, carrying out calculations.
• Pure water is a poor conductor of electrical energy, so the electrolysis of pure water is very slow.
  → If you use salt that will conduct current but not interfere with the reaction, you can increase the rate of the reaction. Sodium Sulfate is used for this purpose.

Question 12

the concentrations of the reactants and products

Answer 12

• The concentrations of the reactants and products is another factor that affects the electrolysis of water. (not 1.0M)
• The concentration of hydrogen ions and hydroxide ions are 1.010-7M, water has a concentration of 55 M.
• Standard reduction potentials cannot be used for predictions or calculations in this case.

Question 13

the chor-alkali process

Answer 13

• Sodium hydroxide and chlorine are key industrial chemicals, with billions of kilograms produced annually in North America.
• Chlorine is used for bleaching, water treatment, disinfectants, hydrochloric acid, and PVC production.
• Sodium hydroxide is essential in pulp and paper processing, soap and detergent manufacturing, aluminum production, and chemical synthesis.
• Both are primarily produced via the chlor-alkali process

Question 14

how does the chor-alkali process work?

Answer 14

• In this process, aqueous sodium chloride is electrolyzed in a cell.
• Chlorine gas forms at the anode, while hydrogen gas and sodium hydroxide form at the cathode.
• These products are separated during production to avoid reactions.
  Sodium hydroxide is periodically extracted and dried for packaging.

Question 15

hydrogen in the choralkali process

Answer 15

• Hydrogen, less commercially used, sometimes fuels sodium hydroxide drying.
• If hydrogen fuel cells become more economical, chlor-alkali hydrogen could see broader use.

Question 16

electrolysis of molten salts

Answer 16

• Pure sodium cannot be obtained by electrolysis in aqueous solutions because water interferes with the reactions.
• Sir Humphry Davy discovered that by heating salts until they melted, he could apply electrolysis to the molten salts.
• Without water present, electrolysis successfully isolates pure sodium.

Question 17

secondary batteries

Answer 17

• Secondary batteries, such as lead-acid batteries in car engines, operate both as galvanic and electrolytic cells.
• When you turn the ignition, the battery functions as a galvanic cell, producing electrical energy through a spontaneous reaction.
• This surge of current starts the engine.

Question 18

what happens to the battery overtime

Answer 18

• To recharge the battery, the car’s alternator, driven by the engine, supplies external electrical energy.
• This reverses the reaction in the cells, which now operate as electrolytic cells, driving the reaction non-spontaneously to restore charge.
• This alternation between galvanic and electrolytic operation is a key feature of all secondary batteries.

Question 19

what does the lead acid battery use?

Answer 19

• The lead-acid battery uses lead and sulfuric acid as its primary materials.
• Each cell contains lead grids: one electrode is packed with powdered lead, and the other with powdered lead(IV) oxide.
• The electrolyte solution is sulfuric acid at a concentration of about 4.5 mol/L.
• This configuration allows the battery to reliably produce and store energy during its operation.

Question 20

what does the lead acid battery consume

Answer 20

• A lead-acid battery consumes lead, lead(IV) oxide, and sulfuric acid during discharge, forming lead(II) sulfate.
• During recharging, these reactions reverse, restoring lead, lead(IV) oxide, and sulfuric acid, enabling repeated use as a galvanic and electrolytic cell.

Question 21

In practice (recharageable batteries)

Answer 21

• In practice, the reversibility of rechargeable batteries is not perfect, and they eventually wear out after many charge/discharge cycles.
• Portable alternatives to lead-acid batteries include rechargeable alkaline batteries and nickel-cadmium (NiCad) batteries, commonly used in portable devices.

Question 22

nickel cadmium

Answer 22

• A nickel-cadmium (NiCad) cell has a potential difference of about 1.4 V. A typical NiCad battery combines three cells in series to produce a voltage suitable for electronic devices.

Question 23

what do nickel-cadmium batteries offer?

Answer 23

• Nickel-cadmium batteries offer benefits but pose risks.
• Repeated use leads to wear, and while recycling is ideal, many end up in landfills.
• Over time, discarded batteries release toxic cadmium, which can enter the food chain.
• Prolonged exposure to low cadmium levels can cause serious health issues, including high blood pressure and heart disease.

Question 24

industrial extraction and refining of metals

Answer 24

• Some metals, like iron, are smelted, while reactive metals such as sodium, lithium, and magnesium are extracted via electrolysis of molten chlorides.
• Aluminum is industrially refined from bauxite using electrolysis, one of the most significant processes.

Question 25

industrial extraction and refining of metals

Answer 25

• Refining, the industrial purification of metals, often uses electrolytic cells.
• For instance, copper extracted at 99% purity is adequate for plumbing but insufficient for electrical wiring,
• requiring further electrolytic refining to achieve the necessary purity.