Chapter 9/19 REDOX | Quizlet

Predict, giving a reason, the direction of movement of electrons when the standard nickel and manganese half-cells are connected.

**Ni2+ is SOA, Mn is SRA

electron movement «in the wire» from Mn(s) to Ni(s)

Eθ «for reduction» of Ni2+ is greater/less negative than Eθ «for reduction» of Mn2+

OR

Ni2+ is stronger oxidizing agent than Mn2+

OR

Mn is stronger reducing agent than Ni

State and explain the products of electrolysis of a concentrated aqueous solution of sodium chloride using inert electrodes. Your answer should include half-equations for the reaction at each electrode.

Positive electrode (anode):2Cl- (aq) → Cl2 (g) + 2e-

Cl- oxidized because higher concentration

OR

electrode potential/E depends on concentration

OR

electrode potential values «of H2O and Cl-» are close

Negative electrode (cathode):2H2O (l) + 2e- → H2 (g) + 2OH- (aq)

OR

2H+ (aq) + 2e- → H2 (g)

H2O/H+ reduced because Na+ is a weaker oxidizing agent

OR

Na+ not reduced to Na in water

OR

H+ easier to reduce than Na+OR

H lower in activity series «than Na»

Accept ⇌⇌.

State the products when a very dilute aqueous solution of magnesium chloride is electrolysed.

Anode (positive electrode):oxygen/O2

OR

hydogen ion/proton/H+ AND oxygen/O2Cathode (negative electrode):hydrogen/H2ORhydroxide «ion»/OH- AND hydrogen/H2

Award [1 max] if correct products given at wrong electrodes.

Predict, giving a reason, the change in cell potential when the concentration of copper ions increases in an voltaic half cell where magnesium half-cell, Mg(s)/Mg2+(aq), is connected to a copper half-cell, Cu(s)/Cu2+(aq).

cell potential increases

reaction moves to the right

OR

potential of the copper half-cell increases/becomes more positive

Accept correct answers based on the Nernst equation

Variable oxidation numbers exist for ____________ and _____________.

Variable oxidation numbers exist for transition metals and for most main-group non-metals.

Explain how the Wrinkler method is carried out.

-sample o the water is saturated with oxygen so the initial

-concentration o dissolved oxygen is known.

-a measured volume o the sample is then incubated at a fxed temperature or fve days while microorganisms in the water oxidize the organic material.

-an excess o a manganese(II) salt is then added to the sample.

Voltaic cells convert energy from _________, __________ chemical processes to electrical energy.

Voltaic cells convert energy from spontaneous, exothermic chemical processes to electrical energy

Describe how an electromotive force is generated.

A voltaic cell generates an electromotive force (EMF) resulting in the movement • of electrons from the anode (negative electrode) to the cathode (positiveelectrode) via the external circuit. The EMF is termed the cell potential (Eo).

Define the standard hydrogen electrode.

The standard electrode potential (Eo) is the potential (voltage) of the reduction half-equation under standard conditions measured relative to the SHE. Solute concentration is 1 mol dm-3 or 100 kPa for gases.

State the Eo of SHE.

Eo of the SHE is 0 V.

When aqueous solutions are electrolysed, water can be ___________ to _____________ at the anode and ___________ to ____________ at the cathode.

When aqueous solutions are electrolysed, water can be oxidized to oxygen at the anode and reduced to hydrogen at the cathode.

State the three factors that affect the amount of product formed at the electrodes during electrolysis.

Current, duration of electrolysis and charge on the ion affect the amount of product formed at the electrodes during electrolysis.

Define electroplating.

Electroplating involves the electrolytic coating of an object with a metallic thin layer.