6.4 Redox
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40. What is used to indicate the oxidation number of an element in a compound?
A Roman numeral.
41. Define a redox reaction.
A reaction that involves simultaneous oxidation and reduction.
42. Define oxidation and reduction in terms of oxygen.
Oxidation is the gain of oxygen, and reduction is the loss of oxygen.
43. How are redox reactions identified in terms of oxygen?
By identifying which substances gain oxygen (oxidized) and which lose oxygen (reduced).
44. Define oxidation and reduction in terms of electrons.
Oxidation is the loss of electrons, and reduction is the gain of electrons.
45. Define oxidation and reduction in terms of oxidation number.
Oxidation is an increase in oxidation number; reduction is a decrease in oxidation number.
46. How are redox reactions identified in terms of electrons?
By identifying reactions where electrons are gained and lost.
47. What is the oxidation number of an element in its uncombined state?
Zero.
48. What is the oxidation number of a monatomic ion?
It is the same as the charge on the ion.
49. What is the sum of the oxidation numbers in a neutral compound?
Zero.
50. What is the sum of the oxidation numbers in a complex ion?
It is equal to the charge on the ion.
51. How can redox reactions be identified using acidified aqueous potassium manganate(VII)?
By a color change from purple to colorless, indicating that the manganate(VII) ion has been reduced (it is an oxidising agent).
52. How can redox reactions be identified using aqueous potassium iodide?
By a color change from colorless to brown, indicating that the iodide ion has been oxidized to iodine (it is a reducing agent).
53. Define an oxidising agent.
A substance that oxidises another substance and is itself reduced.
54. Define a reducing agent.
A substance that reduces another substance and is itself oxidised.
55. How are oxidising and reducing agents identified in a reaction?
By determining which substance loses electrons/increases in oxidation number (reducing agent) and which gains electrons/decreases in oxidation number (oxidising agent).