Chem Electrolysis Notes

Secondary 4 Express Pure Chemistry Page 1 Name: ( Class: 4CYA ) Date: Introduction ▪ We have learnt that ionic compounds conduct electricity only when molten or aqueous. ▪ When an electric current passes through such compounds, they become decomposed in a chemical reaction. ▪ The process of decomposing a compound into its constituent elements by electricity is known as . Electrolytic Cell ▪ A simple electrolytic cell is made up of : - - - - a cell or battery two electrodes an electrolyte other electrical devices ~ bulb, switch, resistor, voltmeter, ammeter. 1 ElectricityElectricity andand ChemistryChemistry

Secondary 4 Express Pure Chemistry Page 2 Electrodes ▪ The plates which carry the electricity into the electrolyte are called electrodes. ▪ They are usually made of inert materials such as carbon (graphite), platinum and mercury. ▪ The electrode connected to the - negative terminal of the battery is called the . - positive terminal of the battery is called the . ▪ The electrodes are also the terminals through which electrons enter and leaves the electrolyte. ▪ Electrons enter via the and leave via the . Electrolyte ▪ An electrolyte is a compound which conducts an electric current when molten or dissolved in water, and is decomposed by the electric current. ▪ Electrolytes are usually : (i) (ii) ▪ Example: ▪ Non- electrolytes are the that do not contain ions . Examples are distilled water, alcohol, oil and other organic solvent. 2 Weak Electrolytes - Weak acids and alkalis Strong Electrolytes - Strong acids, alkalis and salt solution

Secondary 4 Express Pure Chemistry Page 3 Why Can’t Solid Ionic Compounds Conduct Electricity? The ions in solid ionic compounds are held in fixed positions in a lattice. They are unable to move to conduct electricity. Elements and Compounds Conduct Electricity Differently Element - By mobile electrons and element remains unchanged as electricity passes Compound - By mobile ions and Decomposes and forms new substances 3

Secondary 4 Express Pure Chemistry Page 4 Electrolysis When electricity is passed through an electrolyte, chemical decomposition occurs. ▪ This involves the splitting up of the electrolyte into positive and negative ions.▪ - - Positive ions are called . Negative ions are called . During electrolysis, the are attracted to the while are attracted to the