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Chemistry GRADE 12! > chapter 10.2 > Flashcards

chapter 10.2 Flashcards

1
Q

first ever dry cell

A
  • a galvanic cell in which the electrolyte has been thickened to paste.
  • the first ever dry cell was made by Georges Leclanche, he used starch to thicken the electrolyte.
    –> the cell was called Leclanche cell.
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2
Q

Dry cells in the modern age

A
  • modern dry cells are made the same way, we use inexpensive dry cells in electrical devices such as a flashlight, remote contro or an iPod.
  • The lowest priced 1.5V batteries are dry cells.
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3
Q

what is a battery?

A
  • a battery is a lot of galvanic cells connected to each other in series.
  • in the series the negative electrode of one cell is connected to the positive electrode of another cell.
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4
Q

Voltage of a set of cells

A
  • the voltage of a set of cells connected in series is the sum of the voltages of the individual cells.
    ex: a 9V battery contains six 1.5 V dry cells connected in a series.
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5
Q

What is the correct way to use the term battery?

A
  • the term battery is usually used to describe one cell, which is incorrect.
  • a 1.5V dry cell “battery” contains only a single cell – its not a battery.
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6
Q

when does a dry cell stop producing energy?

A
  • a dry cell stops producing electrical energy when all of the reactants are used up.
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7
Q

what happens to batteries when they “die”?

A
  • for a long time, batteries was disposable and discarded when they were all used up.
  • now, a battery that is disposable is called primary battery and a battery that is rechargeable is called a secondary battery.
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8
Q

The inside of a dry cell

A
  • a dry cell has a zinc anode and a inert graphite cathode.
  • The electrolyte is a moist paste of Manganese (IV) oxide, zinc chloride, ammonium chloride, and carbon black.
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9
Q

Alkaline batteries

A
  • billions of alkaline batteries, each contain a single alkaline cell, are made every year.
    –> alkaline battery: a dry cell that has an alkaline (basic) electrolyte in the paste.
  • the ammonium chloride and zinc chloride used in a dry cell are replaced by strongly alkaline (basic) potassium hydroxide.
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10
Q

a button battery?

A
  • a button battery is smaller than an alkaline battery, they are used in small devices.
  • since they are so compact they are used in hearing aids, pacemakers, some caculators and cameras.
  • the development of smaller batteries has an enormous impact on portable devices.
  • they use zinc container, which acts as the anode, an inert stainless stell cathode.
  • In the mercury button battery, the electrolyte paste contains mercury (II) oxide.
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11
Q

the dangers of batteries

A
  • batteries can become dnagerous, they can corrode and the alkaline substances can leak out.
  • they can explode if they are running and burnt, incinerated, releasing toxic heavy metals that are in some batteries.
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12
Q

swallowing cases

A
  • button batteries are so small that they can be swallowed, there is a large number of swallowing cases.
  • more than 60% of these cases are children under 5, between 1-2 years. mainly because of how easily they can be accessed.
  • before they were only used in hearing aids, calculators, camera equipment, now they are used in remote controls, musical or lighted jewelry, greeting cards, shoelaces, and pens.
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13
Q

what happens if a battery is swallowed?

A
  • most of the time it goes through the digestive system and out the body.
  • if it lodges in the esophagus, it can cause serious damage or death, the button batteries that are most likely to lodge in the esophagus are lithium batteries, they are the size of a 5 cent coin.
  • they are large enough to get caught in a childs esophagus, these batteries also generate more power then the others.
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14
Q

what happens if lithium button batteries are lodged in the esophagus?

A
  • the bodily fluids provide an electrolyte for the battery.
  • a current flows through the liquids causing chemical reactions which produce strong alkaline compounds.
  • these compounds can cause severe burns to the tissues, burning holes through the esophagus.
  • The resulting injuries will be extremely serious and maybe fatal. serious damage can begin after 2 hours from swallowing the battery.
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15
Q

what do fuel cells do?

A
  • provide clean electrical energy for transportation as well as industires and homes.
  • a fuel cell is a battery that can be refueled.
  • the reactants flowinto a fuel cell and the products flow of the fuel cell instead of having chemical reactants sealed in a container.
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16
Q

how do the fuel cells convert energy?

A
  • fuel cells directly convert the energy in the fuel into electrical energy, just like a battery, instead of burning the fuel and using the heated gasses to drive an engine or generator.
  • fuel cells ar emore efficient and cleaner than enginers or generators that burn fuel.
  • the major waste product is water.
17
Q

if they are so clean and efficient why are they not found commonly?

A
  • they are not commonly found due to their cost, however many people are working to find ways to reduce the cost and improve the technology.
18
Q

when was the fuel cell first discovered?

A
  • the first demonstration of a fuel cell was done in 1839, by sir william robert grove.
  • in 1889, ludwig mond and charles langer tried to modify it but were unsuccessful, they named it the fuel cell.
  • in 1932, Dr. francis thomas bacon modifyed it successfully, he powered a wielding machine with the fuel cell.
  • however it had yet to become practical or economical.
19
Q

NASA fuel cells

A
  • In 1960, NASA needed a safe efficient, light-weight source of electrical energy and the first practical -expensive- fuel cells were developed.
  • not only was it efficent, but the waste products were pure water, which the astronauts could consume.
20
Q

fuel cell technology

A
  • varioustypes of fuel cells are being developed all based on the principle of the galvanic cell.
  • the main difference is that the chemical reactants are gases that flow past the anode and cathode where the oxidation and reduction half-reactions occur.
  • an electric current then flows through an external cirucit, the gaseous products are eliminated from the cell.
21
Q

first fuel cell made by nasa

A
  • the first fuel cell that was used by NASA was called the proton exchange membrane fuel cell.
  • the anode of a fuel PEM cell is porous carbon coated with platinum to catalyze hydrogen oxdiation.
  • A solid polymer electrolyte allows hydrogen ions to pass while blocking electrons, which flow through an external cirucit to the cathode
  • oxygen from the air at the cathode combines with the returning electrons and hydrogen ions, forming water.
22
Q

the layers of fuel cells.

A
  • a complete fuel cell has many layers of individual cells that together are called a fuel cell stack.
  • PEM fuel cells are 40%-50% eifficnet and work at temps. between 60C and 100C.
  • PEM fuel cells are currently being tested in buses and cars and for electrical energy in homes.
23
Q

another fuel cell like the PEM fuel cell

A
  • another type that is also being tested for this is called the phosphoric acid fuel cell.
  • It has the same oxidation and reduction half-reactions as the PEM cell.
  • those however run on a slightly higher temp. than PEM fuel cells but achieve higher efficences as well. they can also tolerate more impure fuels.
  • the fuel cell used in NASAs Apollo program was called the alkaline fuel cell.
24
Q

how does the alkaline fuel cells insides work?

A
  • The electrolyte is aqueous potassium hydroxide, when hydrogen reaches the anode it combines with the hydroxide ions from the electrolyte and forms water.
  • The electrons travel along with the hydroxide ions from the electrolyte and form water.
  • The electrons travel along the electrode to the external circuit. At the cathode, oxygen gas combines with the electrons that are returning from the external circuit and with water.
25
Q

what temps and how efficient are alkaline cells?

A
  • they operate at about 90C to 100C and are about 40%-50% efficient.
26
Q

hydrogen use in fuel cells.

A
  • Trace amounts of hydrogen gas are found in the atmosphere.
  • Hydrogen for use on fuel cells must be extracted from other compounds, the extraction process requires energy. (electrical energy can split water into hydrogen and oxygen).
  • Hydrogen can be chemically removed from hydrocarbons by a process called reforming, this process also requires energy.
27
Q

what to do wind and solar energies have to do with these processes?

A
  • Wind and solar energies are used for these processes, burning fossil fuels would not benefit in using fuel cells at all.
  • Research to develop fuel cells with internal reformers is underway, systems that remove hydrogen from hydrocarbons.
    → These can use a variety of fuels, such as methane and hydrocarbons.
28
Q

carbon dioxide and hydrogen gas

A
  • Some carbon dioxide is produced but for the amount of energy generated much less carbon dioxide is released than from internal combustion engines or fossil fuel-burning power plants.
  • Progress for another fuel cell called the direct methanol fuel cell is being made.
29
Q

what is corrosion?

A
  • A spontaneous redox reaction between materials and substance in their environment, for example, rusting.
  • Many metals are oxidized by a powerful oxidizing agent in the atmosphere; oxygen.
  • Since metals are usually in contact with oxygen, they are vulnerable to corrosion.
    → sometimes corrosion is described as the oxidation of metals exposed to the environment.
30
Q

how much corrosion happens in north america?

A
  • In North America, 20%-25% of iron and steel produced is used to replace the ones destroyed by corrosion.
  • Not all corrosion is harmful, the green layer formed by it is found attractive by people.
    → Once this layer is formed, patina, it protects the copper underneath from further corrosion.
  • Some artists who work with metals make use of patina for artistic effect.
31
Q

Rust

A
  • Rust is a hydration iron(III) oxide, the surface of a piece of iron behaves as though it consists of many small galvanic cells in which electrochemical reactions form rust.
  • In each small cell, the iron acts as the anode, the cathode is inert and may be an impurity that exists in the iron or is deposited onto it, the cathode could be a piece of soot from the air.
  • Water, from rain, is needed for rusting to occur.
32
Q

carbon dioxide in the air for rust

A
  • Carbon dioxide in the air reacts with rainwater to form carbonic acid, a weak acid.
    → It dissociates into ions, making it an electrolyte for the corrosion process. Other electrolytes, such as road salt can be involved.
  • The circuit is completed by the iron itself, which conducts electrons from the anode to the cathode
33
Q

No barrier in the cell

A
  • No barrier in the cell, Fe2+ and OH- ions mix and form a precipitate of iron(II) hydroxide.
  • The iron(II) hydroxide goes through further oxidation with the oxygen in the air to form iron(III)hydroxide
    iron(II) hydroxide breaks down to form hydrated iron(III) oxide more commonly known as rust.
34
Q

the extent of corroding

A
  • Not all metals corrode to the same extent as iron.
  • Many metals corrode in air, forming a protective oxide layer that prevents further corrosion, as seen with aluminum, chromium, and magnesium.
  • However, iron forms rust, which flakes off and offers little protection against continued corrosion.
35
Q

corrosion prevention of iron?

A
  • Corrosion, especially the corrosion of iron can be very destructive. We put in a lot of effort into corrosion prevention.
  • If iron is kept cool, clean, and dry, it will not corrode, however they are usually outside, exposed to the atmosphere, and it’s not possible to keep them clean, cool, AND dry.
  • The simplest method of corrosion prevention is painting the iron, this prevents air and water from reaching the mental surface.
    → other protective layers are grease, oil, plastic, or a metal that is more resistant to corrosion.
36
Q

chromium protecting bumpers and metal trims on cars

A
  • For example, a layer of chromium protects bumpers and metal trims on cars.
  • Enamel coating is used to protect metal plates, pots, and pans. Enamel is shiny, hard, unreactive glass that can be melted onto a metal surface.
  • A protective layer is only effective if it completely covers the iron, if there’s a hole in the layer, the metal underneath can corrode.
37
Q

Alloys.

A
  • Iron can be protected from corrosion by forming alloys or through galvanization.
  • Stainless steel, an iron alloy with at least 10% chromium, resists rust and is commonly used for items like cutlery and taps but is too costly for large-scale applications like bridges.
38
Q

galvanizing and sacrifical anode

A
  • Galvanizing covers iron with a zinc layer, which protects iron even when damaged.
  • Zinc, acting as a sacrificial anode, a metal that oxidizes more easily than iron and is destroyed to protect an iron object, oxidizes instead of iron, preventing its corrosion until all the zinc is consumed.
39
Q

cathodic protection

A
  • Cathodic protection prevents rusting by attaching a more reactive metal to iron, which acts as a sacrificial anode, leaving iron as the cathode.
  • Unlike galvanizing, the protective metal doesn’t fully cover iron and requires periodic replacement.
  • Protective coatings with less reactive metals, like tin, can have adverse effects if damaged.
  • For instance, in “tin” cans, a scratch in the tin exposes iron, which corrodes faster due to tin acting as the cathode in galvanic cells.
  • Similarly, connecting iron to less reactive metals, such as copper in plumbing, accelerates iron corrosion, as it becomes the anode in the system.

Chemistry GRADE 12! (10 decks)

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