Zinc-carbon battery

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Zinc-carbon battery

A zinc-carbon dry cell
Dry cell

A dry cell is a galvanic electrochemical cell with a pasty low-moisture electrolyte. A wet cell, on the other hand, is a cell with a liquid electrolyte, such as the lead-acid batteries in most cars....
or battery
Battery (electricity)

In electronics, a battery or voltaic cell is a combination of one or more electrochemical cell Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity....
is packaged in a zinc

Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
can that serves as both a container and anode. It was developed from the wet Leclanché cell

Leclanché cell

Georges Leclanch? invented and patented in 1866 his battery, the Leclanch? cell. It contained a conducting solution of ammonium chloride, a cathode of carbon, a depolarizer of manganese dioxide, and an anode of zinc....
. The cathode

Cathode

A cathode is an electrode through which electric charge flows out of a polarized electrical device. Mnemonic: CCD .From an electrochemical point of view, positively charged ion invariably move toward the cathode and/or negatively charged ion move away from it to balance the electrons arriving from external circuitry....
is a mixture of manganese dioxide and carbon

Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
powder. The electrolyte

Electrolyte

An electrolyte is any substance containing free ions that behaves as an electrical conductor medium. Because they generally consist of ions in solution, electrolytes are also known as ionic solutions, but molten electrolytes and solid electrolytes are also possible....
is a paste of zinc chloride

Zinc chloride

Zinc chloride is the name of chemical compound with the chemical formula zincchlorine2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white and highly soluble in water....
and ammonium chloride

Ammonium chloride

Ammonium chloride is, in its pure form, a clear white water-soluble crystalline salt of ammonia. The aqueous ammonium chloride solution is mildly acidic....
dissolved in water.

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Encyclopedia

Zinc

Leclanché cell

Cathode

Carbon

Electrolyte

Zinc chloride

Ammonium chloride

Ammonium chloride is, in its pure form, a clear white water-soluble crystalline salt of ammonia. The aqueous ammonium chloride solution is mildly acidic....
dissolved in water. Zinc chloride cells are an improved version from the original ammonium chloride variety. Zinc-carbon batteries are the least expensive primary batteries

Primary cell

A primary cell is any kind of electrochemical cell in which the electrochemistry chemical reaction of interest is not reversible, so used in disposable battery ....
and thus a popular choice by manufacturers when devices are sold with batteries included. They can be used in remote control

Remote control

A remote control is an Electronics device used for the remote operation of a machine.The term remote control can be contracted to remote or controller....
s, flashlights, toys, or transistor radio

Transistor radio

A transistor radio is a small transistor-based radio receiver. Historically, the term "transistor radio" refers to a radio that is monaural and typically receives only the 540–1600 kilocycle AM broadcast band....
s, where the power drain is not too heavy.

A primary cell

A zinc-carbon dry cell

Dry cell

A dry cell is a galvanic electrochemical cell with a pasty low-moisture electrolyte. A wet cell, on the other hand, is a cell with a liquid electrolyte, such as the lead-acid batteries in most cars....
is described as a primary cell

Primary cell

A primary cell is any kind of electrochemical cell in which the electrochemistry chemical reaction of interest is not reversible, so used in disposable battery ....
because as the cell is discharged, it is not intended to be recharged and must be discarded. "Battery Rejuvenators" were once marketed to restore partially discharged zinc-carbon cells by applying a reverse current to them. However the effects of such devices were only temporary and prone to cause the cell to leak or burst. [https://www.medsun.net/participants/Uploads/100-110_BMIT3802.pdf] Zinc-carbon cells are more likely to leak as the anode is the container. The first ever zinc-carbon battery was invented in Selsdon, Croydon in Greater London in 1834.

Chemical Reactions

The container of the zinc-carbon dry cell is a zinc can. This contains a layer of NH₄Cl with ZnCl₂ aqueous paste separated by a paper layer from a mixture of powdered carbon & manganese (IV) oxide (MnO₂) which is packed around a carbon rod.

In a dry cell, the outer zinc container is the anode (-). The zinc is oxidised according to the following half-equation.

Zn(s) → Zn²⁺(aq) + 2 e^-

A graphite rod surrounded by a powder containing manganese(IV) oxide is the cathode(+). The manganese dioxide is mixed with carbon powder to increase the conductivity

Conductivity

Conductivity may refer to:*Electrical conductivity, a measure of a material's ability to conduct an electric current*Hydraulic conductivity, a property of a porous material's ability to transmit water...
of the cathode mixture. The cathode reaction is as follows:

2MnO₂(s) + 2 H⁺(aq) + 2 e^- → Mn₂O₃(s) + H₂O(l)

The H⁺ comes from the NH₄⁺(aq):

NH₄⁺(aq) → H⁺(aq) + NH₃(aq)

and the NH₃ combines with the Zn²⁺.

In this half-reaction, the manganese is reduced

Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed.This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane , or it can be a complex process such as the oxidation of sugar in the human body through a ser...
from an oxidation state

Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical Electrical charge that an atom would have if all bonds to atoms of different elements were 100% Ionic bond....
of (+4) to (+3).

There are other possible side-reactions, but the overall reaction in a zinc-carbon cell can be represented as:

Zn(s) + 2MnO₂(s) + 2NH₄⁺(aq) → Mn₂O₃(s) + Zn(NH₃)₂²⁺(aq) + H₂O(l)

The battery has an e.m.f. of about 1.5 V

Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
. The approximate nature of the e.m.f is related to the complexity of the cathode reaction. The anode (zinc) reaction is comparatively simple with a known potential. Side reactions and depletion of the active chemicals increases the internal resistance of the battery, and this causes the e.m.f. to drop.

Leakage

When the dry cell has been used for a certain time, the zinc container becomes thinner because zinc metal is oxidised to zinc ions. When the zinc case thins enough, zinc chloride begins to leak out of the battery. The old dry cell is not leakproof. It becomes very sticky as the paste leaks through the holes in the zinc case. The service life of the battery is short, with a shelf life

Shelf life

Shelf life is that length of time that food, drink, medicine and other decomposition items are given before they are considered unsuitable for sale or Eating....
of around 1.5 year

Year

A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, a "Martian year" is the time in which Mars completes its own orbit....
s.

Furthermore, the zinc casing in the dry cell gets thinner slowly, even when the cell is not being used. It is because the ammonium chloride inside the battery is acidic, reacting with the zinc.

The Zinc Chloride Cell

The (heavy duty) zinc chloride cell is an improvement on the original zinc-carbon cell, using purer chemicals and giving a longer life and steadier voltage output as it is used. Instead of an electrolyte mixture containing much NH₄Cl, it is largely only ZnCl₂ paste. The cathode reaction is thus a little different:

MnO₂(s) + H₂O(l) + e^- → MnO(OH)(s) + OH^-(aq)

as is the overall reaction:

Zn(s) + 2 MnO₂(s) + ZnCl₂(aq) + 2 H₂O(l) → 2 MnO(OH)(s) + 2 Zn(OH)Cl(aq)