GAMSAT Physical Chemistry: Redox and Electrochemistry

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Reduction ——— charge number of Oxidant
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increases
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Oxidant ——— charge number of Oxidant
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decreases
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Oxidation ——— in charge number
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increases
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reduction ——— in charge number
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decreases
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Is it possible for the same element to be both oxidized and reduced
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yes given that the element is in two different compounds
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Breathalyzers use redox to detect the presence of ethanol. What color change occurs and why? What is ethanol converted to?
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Orange yellow to green because Cr2O7^(-2) becomes Cr^3+ ethanol becomes acetic acid
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Redox value of an uncombined element
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Redox value of a monatomic ion
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Charge
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Sum of the oxidation states equals …
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Compound charge
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group 1 metals oxidation states
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1+
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group 2 metals oxidation states
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2 +
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Redox value of Fluorine
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-1
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Redox value of H
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+1 excluding metal hybrids where H = -1
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Redox value of O
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-2 excluding peroxides (-1) and F2O (+2)
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Redox value of Cl
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-1 excluding when in compound with F/0
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Oxidation in Organic Chemistry
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an increase in the N, O or halogen content of a compound or a decrease in the H+ content of a compound
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Reduction in Organic Chemistry
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a decrease in the N, 0 or halogen content of a molecule or an increase in the H+ content of a molecule
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Why do the redox definitions differ for Physical and Organic Chemistry?
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The movement of Electrons is not clear in Organic Chemistry
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K2Cr2O7 Oxidizes
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primary alcohols to carboxylic acids secondary alcohols to ketones aldehydes to carboxylic acids alkyl benzenes to aromatic carboxylic acids
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KMnO4 Oxidizes
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primary alcohols to carboxylic acids alkenes to 1,2 – diols aldehydes to carboxylic acids alkyl benzenes to aromatic carboxylic acids
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Pyridinium chlorochromate oxidizes
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primary alcohols to aldehydes
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Ozone plus Zn/H20 oxidizes
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alkenes to aldehydes and ketones
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LiAlH4 reduces
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ketones to secondary alcohols aldehydes to primary alcohols carboxylic acids to primary alcohols acid chlorides to primary alcohols acid anhydrides to primary alcohols esters to primary alcohols amides to amines
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NaBH4 reduces
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ketones to secondary alcohols aldehydes to primary alcohols
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H2 with catalyst (Nickel or Palladium) reduces
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alkenes to alkanes alkynes to alkanes nitriles to amines
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H2 with Lindlars catalyst reduces
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alkynes to Z – alkenes
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Na or Li/NH3 reduces
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alkynes to E – alkenes
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Zn/HCl reduces
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aldehydes to alkanes ketones to alkanes
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Redox is used in
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electrolysis/ electronic cells and galvanic cells
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Define a cell in electrochemistry
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2 electrodes one external wire attaching electrodes ionic medium
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Oxidation at the …
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anode
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Reduction at the ….
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cathode
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Cations to the
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Cathode
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Anions to the
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Anode
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Electrons flow from the …
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Anode to the Cathode
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Galvanic cells
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Produce electricity which is measured in volts and calculated by determining the difference between the standard reduction potentials of the anode and cathode
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Daniel Cell
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Cu2+ is reduced Zn is oxidized 1.1 V is produced
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G = -nFE
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G = Gibbs free energy n = mol of electrons moving F = faradays constant E = cell protection
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Faradays constant
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Magnitude of charge per mol of e- 9.6485 x 10^4 Coulomb/ mol
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The standard way to write galvanic cells is with the Anode on the …
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left
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What is required for a non spontaneous reaction to occur
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an electric current
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Electrolysis
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2 electrodes 1 electrolyte nature of the reaction is that it has non standard reactions
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Faradays law of electrolysis
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The mol of product formed by electrolysis is proportionate to the mol of electrons used in the process of electrolysis
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Mole of e- = (It)/F
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I = amps t = time F = Faradays constant
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Electroplating
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the plated object become the cathode and the metal ions are attracted to it
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Electrolytic corrosion
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two metals with different reduction potentials come into contact through and electrolyte foil and a filing in your teeth
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Dry cell batteries
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1.5 v non-rechargeable oxidation of zinc
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Lead acid batteries
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2v rechargeable can be reversed by electrolysis galvanic cell
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Ni – Cd batteries
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1.4V rechargeable can be reversed by electrolysis galvanic cell

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