redox reactions AOS1 Flashcards
when do oxidation and reduction occur?
they occur simultaneously as electrons are transferred between the reactants
what’s a reducing agent?
species that loses electrons but will cause another reactant to gain electrons
what’s an oxidising agent?
species that gains electrons but will cause another reactant to lose electrons
what are oxidation numbers?
help to identify the oxidising/ reducing agent in the eq, written with their sign then +/- a number
what are the rules for oxidation numbers?
the oxidation number of a free element is 0, oxidation of a simple ion is equal to their charge, hydrogen is +1 but -1 when with hydrides, oxygen is -2 but -1 with peroxides and in compounds with fluorine oxygen has a positive oxidation number, sum of oxidation numbers=overall charge of compound, most electronegative element is assigned the negative oxidation number
what is the oxidation number for transition elements?
they can form ions with several different charges so many transition elements have variable oxidation numbers therefore the presence of Roman numerals in its name indicates the specific oxidation state of the element
oxidation and reduction influence on oxidation numbers?
an increase in oxidation number=oxidation, decrease in oxidation number=reduction, any change in this number means that a redox reaction has occurred
what to do for conjugate redox pairs?
when listing them include the states of both the oxidising/reducing agent and the oxidation number of the oxidising agent is always more positive than that of the reducing agent
how to balance a half-equation in an acidic solution?
first balance oxygens with water, then hydrogens with H+, then charge with electrons
how to balance a half-equation in an alkaline/basic solution?
OH’s are used to balance out the equation instead of H+’s. aqueous hydroxide ions can be used directly to balance a half-equation if there are hydroxide ions in a reactant or product (or both)
how to balance half-equations under basic conditions when OH- isn’t present in a reactant or product?
start by balancing the reaction as if it were in acidic solution by adding H+’s but then after this (and adding the electrons) add hydroxide ions to neutralise the acid and canal out any extra water molecules
how to balance half-equations?
use KOHES