Redox Reactions Flashcards
What are redox processes?
Reactions that involve the transfer of electrons. Redox processes are a category of chemical reactions that involve specific types of chemical change. The two processes always occur together, meaning that if oxidation occurs, then reduction will also occur.
What type of ions do metals form?
Cations (positively charged ions). they lose electrons
what type of ions do nonmetals form?
anions (negatively charged ions). they gain electrons
examples of redox reactions that go by other names
combustion, rusting, and corrosion
↑LEO (goes) GER↓
Oxidation loses electrons (oxidation state/charge increases)
Reduction gains electrons (oxidation state/charge decreases)
defintions of redox reactions
Oxygen: oxidation you gain oxygen, reduction you lose oxygen
hydrogen: oxidation you lose hydrogen, reduction you gain hydrogen
electrons: oxidation you lose electrons, reduction you gain electrons
standard oxidation equation
A –> A + e-
standard reduction equation
A + e- –> A
oxidation state
Oxidation States assign ownership of electrons to all atoms in a given reaction or compound, even when the electrons are shared covalently. In a way, every species is treated as if it were bonded ionically, with the oxidation states as the “pretend charges.”
oxidation numbers
Oxidation numbers are basically another term for oxidation state, but more technically it is when we write the state as a Roman numeral or an integer without a + or - sign. It is not very important to distinguish between oxidation “states” and “numbers” on the IB exam.
modern oxidation definition
an increase in oxidation state.
When an element loses ownership of electrons, its oxidation state increases (less negative/more positive).
modern reduction definition
a decrease in oxidation state.
When an element gains ownership of electrons, its oxidation state decreases (less positive/more negative).
determining oxidation states
1) The element with the greater electronegativity “owns” the electrons in any covalent bond, plus any that exist in its lone pairs.
2) If electronegativity is equal (such as an element bonded to itself), the bonding electrons are split evenly between the covalently bonded atoms.
3)The number of owned electrons compared to its normal # of electrons determines an element’s oxidation state in a given species, in the same way you would determine an ionic charge.
which elements have oxidation states that usually stay the same
oxygen is almost always -2
hydrogen is almost always +1
electrolysis
The process of using electricity to force a non-spontaneous redox reaction.
Electrolysis is used to “split” ionic compounds into their component elements. This means the common products of electrolysis are a metal and a nonmetal.
This results in a conversion of electrical energy to chemical energy, as the products formed by the reaction are less stable and contain more potential energy than the reactants they were formed from.
electrolytic cell
A device that carries out a chemical reaction through electrolysis is known as an electrolytic cell, which is one of two types of electrochemical cells.
molten ionic compounds (+ their role in electrolysis)
Molten ionic compounds are composed of free moving ions at very
high temperatures.
A power supply or battery is connected to the molten ionic compound with wires and electrodes, which for now, we will assume to be inert (a material like graphite or platinum). The power supply provides a potential difference (voltage), mean that one electrode is positive charged and one electrode is negatively charged. The mobile ions will be attracted to the electrode of the opposite charge.
The products formed will be a pure metal and nonmetal. Due to the high temperature, the metal is usually liquid and the nonmetal is usually a gas.
Mnemonics for labelling and describing charge movement in electrolytic cells
VON POE
An Ox and a Red Cat
FAT Cat
Alkali metals (+ reactivity)
The alkali metals are extremely reactive elements. They are never found in pure form in nature (only in compounds). They can, however, be obtained in a lab by means of electrolysis, which separates them out from ionic compounds.
Alkali metals are so reactive that they react spontaneously with something as stable and relatively un-reactive as water. (They also react with air, so they are stored under oil or in vacuum sealed tubes, called ampules).
What is the trend for increasing reactivity (violence/quickness of reactions) down group 1?
The reactivity of Group 1 elements increases as you go down the group because: the atoms get larger. the outer electron gets further from the nucleus. the attraction between the nucleus and outer electron gets weaker – so the electron is more easily lost.
general chemical equation for spontaneous redx reactions with alkali metals and water
2M (s) + 2H2O (l) –> H2 (g) + 2MOH (aq)
The water molecules remove the valence electrons from the alkali metal atoms, producing metal ions (M+). These electrons end up with some of the hydrogen atoms in water, converting them to hydrogen gas (H2). The rest of the water remains in solution as hydroxide ions (OH-), which are highly alkaline/basic.
The reactions are very exothermic, which combined with the hydrogen gas produced, can lead to sparks, flames and, under the right conditions, explosions.
*M stands for the alkali metal
Spontaneous redox reactions
In addition to electrolysis, there are a huge number of redox reactions that occur spontaneously. These include combustion reactions, the rusting of iron, amongst many others.
One specific type of redox reaction is a single-replacement reaction.
Non spontaneous reaction
essentially the opposite of a spontaneous reaction. for example, tin metal reatcs spontaneously with silver nitrate. this means that the reverse reaction will be non-spontaneous. so if we put silver into a solution of tin (II) ions, a reaction will not occur.
oxidising agent
The oxidizing agent causes another species in the reaction to lose electrons/ increase its oxidation state (ie: it causes oxidation). its always the one that gets reduced.
reducing agent
The reducing agent causes another species in the reaction to gain electrons/ decrease its oxidation state (ie: it causes reduction). it’s always the one that gets oxidised.
activity series
An Activity Series is a ranking of a group of elements for a particular type of reactivity. It is most common to see an activity series as a ranking of elements for their relative strength as reducing agents.
In application: we can test and observe whether or not reactions take place spontaneously between reactants and use that data to rank elements for how reactive they are as reducing agents. We can do the same for oxidizing agents.
how does an activity series of work
We can predict spontaneous reactions between metals & metal ions by adding in the metal ions to this activity series.
* Electrons are spontaneously given down the series, from stronger reducing agents, to the ions of weaker reducing agents. Metals lower down in the series are NOT capable of reducing the ions above them.
* The Metals with the greatest “activity” are the most reactive metals. They easily lose electrons and are therefore the Strongest Reducing Agents. The least active metals are very unreactive, very stable metals.
* H represents acid, which is more appropriately shown as H+ ions. Metals above H will react in acids, producing hydrogen gas and metal ions, metals below H will generally not react in acids.
What is table 19 designed for?
it’s designed to be used to determine the potential difference (voltage) created when a spontaneous redox reaction is used ot generate electricity.
