iGCSE Chemistry (0620) Core:4.1 Electrolysis: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Looking at the cell diagram, X is connected to the positive terminal of the power supply, which makes it the anode. Y is attached to the negative terminal, so that is the cathode. Z is the substance the electrodes dip into that conducts the current, which is the electrolyte. For electrolysis to work, the ions must be free to move around, so the salt needs to be dissolved in water (aqueous) or melted. Solid salt won’t work. So A has everything labelled perfectly.
▶️ Answer/Explanation
Detailed solution:
Molten potassium bromide ($\text{KBr}$) contains potassium ions ($\text{K}^+$) and bromide ions ($\text{Br}^-$). During electrolysis, the positive potassium ions move to the negative cathode and gain electrons to form potassium metal. The negative bromide ions move to the positive anode and lose electrons to form bromine gas. So, bromine at the anode and potassium at the cathode is correct.
▶️ Answer/Explanation
Detailed solution:
When concentrated aqueous sodium chloride (brine) is electrolysed, the ions present are Na⁺, Cl⁻, H⁺, and OH⁻. At the positive electrode (anode), oxidation occurs and negative ions are attracted. In a concentrated solution, chloride ions (Cl⁻) are discharged in preference to hydroxide ions (OH⁻). So chlorine gas (Cl₂) is produced as the main product at the anode. Hydrogen forms at the cathode, and sodium is not produced in aqueous solution.