DAILY QUESTIONS

• Circle the oxidized element, underline the reduced element.

2Sr +O2 2SrOFe+2 +O2 FeO

• Define what happens to elements that are oxidized and reduced.

OBJECTIVES:

C5.1 State that electrolysis is the chemical effect of electricity on ionic compounds, causing them to break up into simpler substances, usually elements

C5.2 Use the terms electrode, electrolyte, anode and cathode

C5.4 Describe the electrode products, using inert electrodes, in the electrolysis of:

• molten lead bromide

• aqueous copper chloride

• dilute sulfuric acid

ELECTROLYSIS APPARATUS

ElectrodeElectrode

Electrolyte

Electrode - an electrical conductor which carries charge to or from a liquid undergoing electrolysis.

Electrolyte - a molten or aqueous solution through which an electrical current can flow.

ELECTROLYSIS APPARATUS

CathodeAnode

Electrolyte

-+

Cathode:The negatively charged electrode. Attracts positively charged ions (cations).

Anode:The positively charged electrode. Attracts negatively charged ions (anions).

• Electrolysis only happens in: - molten ionic liquids or - aqueous solutions containing ions.

• There must be a complete circuit.

• A lamp or ammeter can be used to show that electricity is flowing around the circuit.

ELECTROLYSIS OF ZINC CHLORIDE

In your journal:

Describe what is occurring during the electrolysis of zinc chloride.

DEMO TIM

E

EL E

CT

RO

LYS

I S

ELECTROLYSIS

• Introducing electricity to a mixture can cause a chemical reaction to occur.

• However, this requires that the atoms involved become ions• Define ions

FORMING IONS

Na

Cl

FORMING IONS

Na

Cl Cl-

Na+

BONDING

The outer shell is full, but the ions are not neutral. How can neutrality be achieved?

Na+ Cl-

IONIC BONDING

An ionic bond is a strong electrostatic force of attraction between oppositely charged ions

[Na]+ [Cl]-

LET’S TRY A FEW

• Lithium & Fluorine• Magnesium & Fluorine

CONDUCTIVITY

Conductivity is the ability of a substance to conduct electricity.

For a substance to conduct electricity, “free” electrons have to be available

Free electrons = electrons that are able to move

CONDUCTIVITY IN METALS

• Electrons move• Metals can be in solid or

liquid form• No chemical change takes

place• Examples: copper wire; aluminum

pan

CONDUCTIVITY IN IONIC COMPOUNDS

• Ions move• Ionic compounds can be in liquid

(molten) form or in aqueous solution

• Chemical change takes place• Examples: molten lead bromide, sodium

chloride solution, copper(II)sulfate solution

Cathode (-)

(negative electrode)

Positive ions go here (cations).

As metal ions are positive, they go to the cathode.

Ions gain electrons. They are reduced and become neutral atoms.

Anode (+)

(positive electrode)

Negative ions go here (anions).

As non-metal ions are negative, they go to the anode.

Ions lose electrons. They are oxidised and become neutral atoms

(which react together to form molecules).

AT THE ELECTRODES

ELECTROLYSIS OF COPPER CHLORIDE

Electrolyte:CuCl2 (aq)

+ -

In your journal:

For the electrolysis of copper chloride:1. Identify the ions

present in the electrolyte.

2. Describe the movement of ions.

ELECTROLYSIS OF SOLUTIONS – CATHODE

For solutions of highly reactive metals: Hydrogen gas, not the metal, is produced at the cathode.

For metals that are more reactive than hydrogen, the metal will stay in the solution and hydrogen gas will be produced.

ELECTROLYSIS OF SOLUTION - CATHODE

ELECTROLYSIS OF SOLUTIONS-ANODE

The product at the anode depends on:

The negative anions present in the solution.

Homework:• Read the lab report• Grade based on the

rubric provided• Missing Coursework-

Come in Thursday• Missing homework-

fill form then turn in.