Applications Of Electrolysis

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What is Electroplating?

Electroplating coats the surface of one metal with a layer of a different metal using electrolysis.
The cathode (negative electrode) is the object to be plated.
The anode (positive electrode) is made of the pure metal that will be plated onto the object.
The electrolyte is an aqueous solution of a soluble salt of the anode metal (e.g., tin(II) chloride for tin plating).
At the anode: metal atoms lose electrons (oxidation) and go into solution as ions.
At the cathode: metal ions gain electrons (reduction) and deposit as metal atoms on the object.
Example half-equations for tin plating: Anode: Sn(s) → Sn²⁺(aq) + 2e⁻; Cathode: Sn²⁺(aq) + 2e⁻ → Sn(s).

Uses of Electroplating

To improve appearance – e.g., silver-plating cutlery and jewellery.
To increase resistance to corrosion – e.g., chromium and nickel plating, galvanising (zinc coating on iron/steel).
To reduce wear or provide a harder surface.

Electroplating Setup

The object to be plated must be very clean and free of grease to ensure good adhesion.
The anode must be the same metal as the plating layer (e.g., silver anode for silver plating).
The electrolyte must contain ions of the plating metal (e.g., silver nitrate for silver plating).
The power supply provides direct current; the object is connected to the negative terminal.

Electroplating a strip of iron with tin

Hydrogen Fuel Cells – Basics

A fuel cell is an electrochemical cell that converts chemical energy from a fuel into electricity.
In a hydrogen-oxygen fuel cell, hydrogen is the fuel and oxygen is the oxidant.
The only product is water; no pollutants are produced.
Overall reaction: 2H₂ + O₂ → 2H₂O (hydrogen + oxygen → water).
At the anode: H₂ → 2H⁺ + 2e⁻ (oxidation of hydrogen).
At the cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O (reduction of oxygen).
The electrolyte (e.g., potassium hydroxide solution) allows ion flow between electrodes.

Hydrogen-oxygen fuel cell

Advantages of Hydrogen Fuel Cells (Extended)

No pollutants – only water is produced, unlike petrol engines which emit CO₂, NOₓ, and CO.
High efficiency – more energy per kilogram than petrol or diesel.
Renewable – hydrogen can be produced by electrolysis of water using renewable electricity.

Disadvantages of Hydrogen Fuel Cells (Extended)

Hydrogen production – most hydrogen currently comes from fossil fuels (releases CO₂); electrolysis requires large amounts of electricity.
Storage and safety – hydrogen is highly flammable and requires high-pressure tanks, making storage difficult and expensive.
Cost and infrastructure – fuel cell materials are expensive; very few hydrogen filling stations exist.

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練習問題

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1.What is electroplating?
Easy
- ACoating the surface of one metal with a layer of a different metal
- BExtracting metals from their ores using electricity
- CBreaking down a compound using heat
- DA method of sacrificial protection
2.In electroplating, the object to be plated is connected to which electrode?
Easy
- AThe negative electrode (cathode)
- BThe positive electrode (anode)
- CThe electrolyte
- DThe power supply
3.What is the product of the reaction in a hydrogen fuel cell?
Easy
- AWater
- BHydrogen peroxide
- COxygen
- DCarbon dioxide
4.Which half-equation represents the reaction at the cathode when electroplating an iron spoon with silver?
Medium
- AAg⁺ + e⁻ → Ag
- BAg → Ag⁺ + e⁻
- CFe²⁺ + 2e⁻ → Fe
- DFe → Fe²⁺ + 2e⁻
5.Which substance is used as the electrolyte when electroplating an iron spoon with copper?
Easy
- AAqueous copper nitrate
- BAqueous iron nitrate
- CCopper rod
- DIron rod
6.In a hydrogen fuel cell, what happens to hydrogen at the anode?
Medium
- AHydrogen is oxidised to form H⁺ ions and electrons
- BHydrogen is reduced to form H⁻ ions
- CHydrogen combines with oxygen to form water
- DHydrogen is produced from water
7.Which of the following is a disadvantage of using hydrogen fuel cells in cars?
Easy
- AHydrogen is difficult to store safely
- BThe only product is water
- CFuel cells are very quiet
- DHydrogen is a renewable fuel
8.Why does the concentration of metal ions in the electrolyte remain constant during electroplating?
Medium
- AMetal ions are removed at the cathode and replenished at the anode at the same rate
- BThe electrolyte is continuously stirred
- CMetal ions are neither produced nor consumed
- DThe power supply is alternating current

もっと問題

9.Which of the following is a reason for electroplating an object?
Easy
- ATo improve appearance
- BTo increase its mass
- CTo make it magnetic
- DTo lower its melting point
10.In electroplating, the anode is made from which material?
Easy
- AThe pure metal that will be plated onto the object
- BThe same metal as the object being plated
- CAn inert metal like platinum
- DThe electrolyte solution
11.What is the balanced symbol equation for the overall reaction in a hydrogen fuel cell?
Medium
- A2H₂ + O₂ → 2H₂O
- BH₂ + O₂ → H₂O₂
- C2H₂ + O₂ → 2H₂O₂
- DH₂ + O → H₂O
12.Which of the following statements about electroplating is correct?
Medium
- AThe object to be plated is the cathode
- BThe electrolyte is always a solid
- COxidation occurs at the cathode
- DThe anode is made of the same metal as the object
13.In the electroplating of a steel spoon with silver, the spoon must be very clean and free of grease. What is the most likely reason for this?
Medium
- ATo prevent the silver from reacting with grease
- BTo ensure the silver layer adheres properly to the spoon
- CTo reduce the amount of electricity needed
- DTo avoid contamination of the electrolyte
14.In a hydrogen fuel cell, which substance undergoes oxidation?
Easy
- AOxygen
- BWater
- CHydrogen
- DPotassium hydroxide
15.The overall reaction in a hydrogen fuel cell is 2H2 + O2 → 2H2O. What is the ratio of hydrogen to oxygen consumed in the reaction?
Easy
- A1:1
- B2:1
- C1:2
- D3:1
16.In the electroplating of an iron object with nickel, the electrolyte used is aqueous nickel(II) sulfate. During the process, the concentration of nickel ions in the electrolyte remains constant. Which statement explains this?
Medium
- ANickel ions are reduced at the cathode and oxidised at the anode at equal rates
- BNickel ions are produced at the cathode and used up at the anode
- CThe electrolyte is replenished by adding more nickel sulfate
- DNickel ions do not participate in the reaction
17.A hydrogen fuel cell produces electricity with water as the only product. If methane (CH4) were used as the fuel instead, which additional product would be formed?
Medium
- ACarbon dioxide
- BCarbon monoxide
- CMethanol
- DHydrogen peroxide
18.In a hydrogen fuel cell, the half-equation at the cathode is O2 + 4H+ + 4e− → 2H2O. What is the half-equation at the anode?
Medium
- AH2 → 2H+ + 2e−
- B2H+ + 2e− → H2
- CO2 + 2H2O + 4e− → 4OH−
- D4OH− → O2 + 2H2O + 4e−
19.Which of the following is a disadvantage of using hydrogen fuel cells in vehicles?
Easy
- AThey produce harmful pollutants
- BHydrogen is difficult to store safely
- CThey are less efficient than petrol engines
- DThey require frequent recharging
20.In the electroplating of a steel spoon with silver, the anode is made of silver. What is the purpose of the anode?
Medium
- ATo provide a source of silver ions for the electrolyte
- BTo be plated with silver
- CTo complete the electrical circuit
- DTo reduce silver ions to silver metal
21.A student wants to electroplate an iron rod with copper. Which electrolyte should be used?
Easy
- AAqueous iron(II) sulfate
- BAqueous copper(II) sulfate
- CAqueous silver nitrate
- DPure water
22.In a hydrogen fuel cell, which substance acts as the electrolyte?
Easy
- AHydrogen gas
- BOxygen gas
- CPotassium hydroxide solution
- DWater
23.In a hydrogen fuel cell, hydrogen enters at one electrode and oxygen enters at the other. Which electrode is the anode?
Medium
- AThe electrode where hydrogen enters
- BThe electrode where oxygen enters
- CThe electrolyte
- DThe external circuit
24.In the electroplating of a steel spoon with silver, the spoon is first cleaned and degreased. Which of the following is the most likely reason for this step?
Medium
- ATo ensure good contact between the electrolyte and the spoon so the silver adheres evenly
- BTo ensure the spoon is negatively charged
- CTo increase the conductivity of the spoon
- DTo prevent the silver from reacting with grease
25.A student electroplates an iron rod with nickel. The electrolyte is aqueous nickel(II) sulfate. Which half-equation correctly represents the reaction at the cathode?
Medium
- ANi → Ni2+ + 2e−
- BNi2+ + 2e− → Ni
- CNi + 2e− → Ni2+
- DNi2+ → Ni + 2e−
26.In a hydrogen fuel cell, the half-equation at the anode is H2 → 2H+ + 2e−. Which of the following describes the role of hydrogen in this reaction?
Easy
- AHydrogen is reduced as it gains electrons
- BHydrogen is oxidised as it loses electrons
- CHydrogen acts as the electrolyte
- DHydrogen is the oxidising agent
27.Which of the following is a suitable electrolyte for electroplating an iron spoon with copper?
Easy
- AAqueous iron(II) nitrate
- BAqueous copper(II) nitrate
- CCopper rod
- DIron rod
28.Which of the following materials would NOT be suitable for electroplating?
Easy
- AIron
- BCopper
- CGlass
- DSteel
29.A student sets up an electrolysis cell to electroplate an iron rod with nickel. The iron rod is connected to the positive terminal of the power supply, and a nickel strip is connected to the negative terminal. The electrolyte is aqueous nickel(II) sulfate. What error has the student made?
Medium
- AThe electrolyte should contain iron ions
- BThe iron rod should be connected to the negative terminal
- CBoth electrodes should be made from iron
- DThe circuit should contain a switch
30.In the electroplating of a steel object with copper, the concentration of copper(II) ions in the electrolyte remains constant. Which of the following explains this?
Medium
- ACopper ions are neither produced nor consumed at the electrodes
- BCopper atoms from the anode dissolve to replace copper ions deposited at the cathode
- CThe electrolyte is replenished by adding more copper sulfate crystals
- DCopper ions are recycled by the power supply
31.A hydrogen fuel cell uses hydrogen and oxygen to produce electricity. Which of the following is a disadvantage of using hydrogen fuel cells in cars?
Easy
- AThe only product is water, which is harmless
- BHydrogen is a renewable fuel
- CHydrogen is difficult to store safely
- DFuel cells produce no noise pollution
32.A student investigates electroplating by coating a copper coin with zinc. The coin is connected to the negative terminal of a power supply, and a zinc electrode is connected to the positive terminal. The electrolyte is aqueous zinc sulfate. After 10 minutes, the coin is removed and weighed. Which of the following would be observed?
Medium
- AThe coin loses mass as copper dissolves
- BThe coin gains mass as zinc is deposited
- CThe zinc electrode gains mass as zinc is deposited
- DThe electrolyte becomes colourless
33.Which of the following is an advantage of using a hydrogen fuel cell compared to a petrol engine?
Easy
- AHydrogen is cheaper than petrol
- BThe only product is water, so no pollutants are produced
- CHydrogen fuel cells are more efficient at low temperatures
- DHydrogen is a liquid at room temperature
34.In an experiment, a student electroplates an iron nail with copper using a copper anode and aqueous copper(II) sulfate as electrolyte. The student uses a variable resistor to control the current. Which of the following changes would increase the mass of copper deposited on the nail in a given time?
Medium
- ADecreasing the current
- BIncreasing the current
- CUsing a larger iron nail
- DUsing a more concentrated electrolyte
35.A student electroplates an iron rod with copper using a copper anode and aqueous copper(II) sulfate. After some time, the concentration of copper(II) ions in the electrolyte is found to be unchanged. Which statement explains this observation?
Medium
- ACopper ions are reduced at the cathode and oxidised at the anode at equal rates
- BCopper ions are not consumed because the electrolyte is a catalyst
- CThe anode dissolves but no copper is deposited on the iron
- DThe iron rod prevents the copper ions from reacting
36.In a hydrogen fuel cell, the overall reaction is 2H2 + O2 → 2H2O. If 4 moles of hydrogen are used, how many moles of oxygen are consumed and how many moles of water are produced?
Medium
- A2 moles of oxygen and 4 moles of water
- B1 mole of oxygen and 2 moles of water
- C4 moles of oxygen and 4 moles of water
- D2 moles of oxygen and 2 moles of water
37.In an experiment, a student electroplates an iron nail with copper using a copper anode and aqueous copper(II) sulfate as electrolyte. The student uses a variable resistor to change the current. Which of the following would happen if the current is increased?
Medium
- AMore copper is deposited per unit time
- BLess copper is deposited per unit time
- CThe iron nail becomes coated with a thicker layer of copper overall
- DThe copper anode dissolves more slowly
38.A student investigates electroplating by coating a copper coin with zinc. The coin is connected to the negative terminal of a power supply, and a zinc electrode is connected to the positive terminal. The electrolyte is aqueous zinc sulfate. After 10 minutes, the coin is removed and dried. Which of the following is observed?
Easy
- AThe coin has a silvery coating
- BThe coin has a reddish coating
- CThe coin remains unchanged
- DThe zinc electrode becomes coated with copper
39.In electroplating, which electrode is the object to be plated connected to?
Easy
- Athe positive terminal (anode)
- Bthe negative terminal (cathode)
- Ceither terminal depending on the metal
- Da separate earth terminal
40.Electroplating is a process where the surface of one metal is coated with a layer of a different metal.
Easy
True or false?
41.Which half-equation correctly represents the reaction at the anode when electroplating an iron strip with tin?
Medium
- ASn²⁺(aq) + 2e⁻ → Sn(s)
- BSn(s) → Sn²⁺(aq) + 2e⁻
- CFe(s) → Fe²⁺(aq) + 2e⁻
- DSn²⁺(aq) + 2e⁻ → Sn(l)
42.In a hydrogen fuel cell, oxygen is reduced at the cathode.
Easy
True or false?
43.Which of the following is an advantage of hydrogen fuel cells compared to petrol engines?
Easy
- AThey produce carbon dioxide as the only product.
- BThey are cheaper to manufacture.
- CThey produce no pollutants, only water.
- DHydrogen is easier to store than petrol.
44.Select all the disadvantages of hydrogen fuel cells from the following list.
Medium
- AHydrogen is highly flammable and difficult to store safely.
- BThe only product is water.
- CMost hydrogen is currently produced from fossil fuels.
- DFuel cells release more energy per kilogram than petrol.
- EThere are very few hydrogen filling stations.
45.Match each electrode in electroplating with its correct role.
Easy
- Cathode
- Anode
- Object to be plated
- Made from the pure plating metal
46.Arrange the following steps in the correct order for electroplating an iron strip with tin.
Medium
- Tin ions gain electrons at the cathode.
- Tin atoms lose electrons at the anode.
- Tin atoms deposit on the iron strip.
- Tin ions enter the electrolyte.
47.Complete the sentence:
Easy
In electroplating, the anode is made from the ____ that will be plated onto the object.
48.State the purpose of galvanising.
Easy
49.In a hydrogen fuel cell, the overall reaction is 2H₂ + O₂ → 2H₂O. How many moles of water are produced when 6 moles of hydrogen are consumed?
Medium
50.Complete the sentence about electroplating.
Easy
In electroplating, the object to be plated is connected to the ____ electrode, and the anode is made from the pure ____ that will be plated.
51.State one chemical advantage of using a hydrogen fuel cell over a petrol engine.
Medium
52.In a hydrogen fuel cell, the overall reaction is 2H₂ + O₂ → 2H₂O. How many moles of water are produced when 6 moles of hydrogen are consumed?
Medium
- A7 mol
- B8 mol
- C6 mol
- D5 mol

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