redox reactions AOS1

Question 1

when do oxidation and reduction occur?

Answer 1

they occur simultaneously as electrons are transferred between the reactants

Question 2

what’s a reducing agent?

Answer 2

species that loses electrons but will cause another reactant to gain electrons

Question 3

what’s an oxidising agent?

Answer 3

species that gains electrons but will cause another reactant to lose electrons

Question 4

what are oxidation numbers?

Answer 4

help to identify the oxidising/ reducing agent in the eq, written with their sign then +/- a number

Question 5

what are the rules for oxidation numbers?

Answer 5

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

Question 6

what is the oxidation number for transition elements?

Answer 6

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

Question 7

oxidation and reduction influence on oxidation numbers?

Answer 7

an increase in oxidation number=oxidation, decrease in oxidation number=reduction, any change in this number means that a redox reaction has occurred

Question 8

what to do for conjugate redox pairs?

Answer 8

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

Question 9

how to balance a half-equation in an acidic solution?

Answer 9

first balance oxygens with water, then hydrogens with H+, then charge with electrons

Question 10

how to balance a half-equation in an alkaline/basic solution?

Answer 10

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)

Question 11

how to balance half-equations under basic conditions when OH- isn’t present in a reactant or product?

Answer 11

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

Question 12

how to balance half-equations?

Answer 12

use KOHES