Unit 3 Flashcards
what is electrochemistry
Electrochemistry is a branch of chemistry that deals with reactions that convert chemical energy into electrical energy and vice versa.
what are practical uses of electrochemistry (3)
- chemical reactions in batteries
- corrosion of metals
- electrical impulses in our bodies
what is oxidation
the loss of electrons
what is an example of oxidation
apples turning brown when they get exposed to the air
what is reduction
the gain of electrons
what is an example of reduction
iron metal ruts because of it’s reaction with oxygen
how do you tell which one is being reduced
the one that starts with the charge is reduced because it gain electrons
how do you tell which one is being oxidized
the one that starts with no charge is oxidized because it lost electrons
how do you know which one is the reducing agent
the one that was oxidized is the reducing agent
how do you know which one is the oxidizing agent
the one that was reducing is the oxidizing agent
what is a redox reaction
a chemical reaction with both a reduction and oxidation
give an example of a redox reaction
Mg(s) + Cu2+(aq) –> Cu(s) + Mg2+(aq)
what is the purpose of a half reactionary
to make it easier to follow the transfer of electrons they make them into half reactions so oxidation and reduction can be represented seperatly
in a redox reaction why does the oxidizing agent undergo reduction
In a redox reaction the oxidizing agent accepts the electrons from the reactant being oxidized. Since the oxidizing agent is gaining electrons it is reduced.
do you include the front numbers when doing the half reactions
yes
what is the purpose of the galvanic cell
a device that converts chemical energy into electrical energy through redox reactions
how does it work
the reactants in the redox reaction do not come into direct contact with each other, so the electrons are forced to travel through an external wire, or circuit.
what are half-cells
The compartments of a galvanic cell, including the electrodes.
who developed the galvanic cell and when
In 1836, John Frederick Daniell developed a galvanic cell
what electrodes
A conducting substance through which electrons can enter or leave the cell.
what is the anode (2)
- The anode is the negative electrode where oxidation takes place.
- It is the source of electrons, and the negative terminal of the galvanic cell.
what is the cathode (2)
- The cathode is the positive electrode where reduction takes place.
- It receives electrons and is the positive terminal of the galvanic cell.
what is a electrolyte
A substance that conducts electricity when it is dissolved in water.
what is a porous barrier or salt bridge
Allows the flow of ions to maintain a neutral charge in the half-cells, while preventing the ions in the cathode half-cell from coming in direct contact with the anode.
what is the external circuit/wire
Connects the anode and the cathode together to allow electrons to flow from the anode to the cathode in an external circuit.
what is the voltmeter/load
A voltmeter can be connected into the external circuit to measure the amount of electricity produced. Alternatively, an electrical load, such as a light, can be connected into the circuit.
how does the activity series work
In a galvanic cell, electrons always flow from the anode to the cathode in the external circuit. The anode, the metal that is oxidized, is the more reactive metal of the two based on the activity of series of metals.
how do you complete the galvanic cell
- To complete the circuit of the galvanic cell, the two half-cells must be connected, but the contents of the half-cells not allowed to mix. - To complete the circuit the half-cells are usually connected by a porous barrier, or a salt bridge.
what does the salt bridge do
The porous barrier or salt bridge allows the flow of ions to maintain a neutral charge in the half-cells, while preventing the copper (II) ions from coming in direct contact with the zinc electrode.
the anode is the more ________ metal and it belongs on the ______ of the ______ _______
reactive
left
cell
notation
What is the direction of electron flow in the external circuit of a galvanic cell?
Electrons always flow from the anode to the cathode in a galvanic cell.
In a galvanic cell, in what direction do positive ions migrate to maintain a neutral charge in the half-cells?
Positive ions migrate towards the cathode.
In a galvanic cell, in what direction do negative ions migrate to maintain a neutral charge in the half-cells?
Negative ions migrate towards the anode.
What would happen if the half-cell compartments of a galvanic cell were not connected?
If the flow of ions did not occur a charge difference would develop between the half-cells and the reaction would stop.
what redox reactions used for
chemical analysis
electroplating and metal purification
industrial chemicals
batteries
explain chemical analysis
Many glucose sensors used by diabetics and the breathalyzer test used to test suspected drunk drivers are tests based on redox reactions.
explain industrial chemicals
- Electrochemical processes are used to produce a variety of chemicals used in industry and in the home.
- Electricity is used in an electrochemical process called the chlor-alkali process to produce hydrogen and chlorine gases and sodium hydroxide from sodium chloride and water.
what is a battery made of
A battery basically consists of two or more galvanic cells connected together in series to increase the amount of electricity produced.
what are primary cells
Primary cells, also called dry cells, are your typical disposable batteries used in various electrical devices.
what are primary cells used in
flashlights
watches
kids’ toys
why can you only use them once
Primary cells are based on irreversible redox reactions so that when the reactants are used up, the battery can no longer produce electricity.
what is electroplating
Electroplating is when a corrosion resistant or decorative metal coating is applied to a metal object.
how do they do electroplating
Electroplating is done by making the metal object to be coated the cathode of an electrochemical cell, which results in metal atoms “plating out” on to the cathode.
what eles is electroplating used for
Certain types of metals are also extracted from their mineral ore using electrochemical processes and redox reactions.
what is corrosion
Corrosion is a natural electrochemical process where metals are oxidized by substances in the environment, returning the metal to a mineral-like state.
what is an example of corresion
the pennies going green after a certain period of time
what is and example reaction of corresion
4Al(s) + 3O2(g) –> 2Al2O3(s)
how does corresion slowly get stopped
The metal creates a thin protective layer of metal oxide or some other metal compound, which adheres to the metal, and slows down further corrosion.
what metals create a thin layer to slow corresion
aluminum, magnesium, and copper
what happens iron when it corredes
Since the rust produced when iron corrodes flakes off and does not adhere to the metal surface, the underlying iron is exposed and results in further corrosion, eventually destroying the object.
why is the corresion of metal so bad
iron-based metals are so widely used, and corrosion greatly reduces the useful life of iron products.
what has to be present for iron to corrode
water and oxygen
what is rust
rust, which is a mixture of reddish-brown iron(III) hydroxide and hydrated iron(III) oxide.
In the redox reaction of the corrosion of iron which substance is reduced?
oxygen
name three factors that affect the rate of corresion
- low pH acidic solotions such as those caused by acid rain promote corresion of iron
- metal objects that get bent and re-shaped are more prone to corresion
- Contact with other metals has varying affects on the rate of iron corrosion. Contact with less reactive metals promotes corrosion, while contact with more reactive metals inhibits corrosion.
what are metal alloys
An alloy is a mixture of metals, and sometimes other elements, such as carbon (used to make steel).
what is a common iron alloy
stainless steel
what does stainless steel contain
chromium, carbon, and sometimes other metals.
whats good about stainless steel
Stainless steel is much more resistant to corrosion than pure iron
what is stainless steel used for
used for cutlery, water faucets, and marine hardware, where corrosion resistance is very important.
what is a protective coating
A protective coating creates a barrier preventing water and air from coming in direct contact with the iron.
what is bad about protective coatings
The problem with protective coatings is that they are only good as long as they completely cover the surface of the iron; if the coating is broken, the metal underneath can start to corrode.
what is an example of protective coating
such as the underside of vehicles, rust proofing by applying a coating of oil, or grease is commonly used
what is iron plated with
chromium, zinc, or tin.
why can’t we build big thing out of stainless steel
because chromium is really expensive
what is cathode protection
Cathodic protection relies on the redox reactions that occur in galvanic cells to protect iron objects from corrosion.
how does it work
In cathodic protection, the iron object is forced to act as a cathode by supplying it with electrons preventing it from being oxidized.
what are scarficial anodes and where are they used
Magnesium, zinc, and aluminum are commonly used as sacrificial anodes. Sacrificial anodes are commonly attached to ships’ hulls, marine engines, and underground pipelines and storage tanks to help prevent corrosion.
what is galvanization
Often protective coatings and cathodic protection methods are used together to inhibit the corrosion of iron.
give an example of galvanization
involves coating an iron object in a protective layer of zinc
how does zinc protect iron
- protects iron from water and oxygen
- So if the zinc protective layer is broken the zinc will act as a sacrificial anode and be oxidized to zinc ions.
what are examples of galavanzed products
chain link fences and exterior nails
What would be one drawback of using an impressed current to provide corrosion protection?
A constant electricity source is needed to create the impressed electrical current.
