Competing Ions in Electrolysis Quiz
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5 questions, one answer each
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1. What mainly determines which ion is discharged at the cathode when more than one positive ion is present?
- A. The concentration of the ions
- B. The reactivity of the elements involved
- C. The temperature of the electrolyte
- D. The size of the electrode
2. What mainly determines which ion is discharged at the anode when more than one negative ion is present?
- A. The reactivity of the non-metals
- B. The relative concentrations of the ions
- C. The colour of the ions
- D. The size of the anode
3. Electrolysis of concentrated sodium chloride solution is carried out. What forms at the cathode?
- A. Sodium metal
- B. Hydrogen gas
- C. Chlorine gas
- D. Oxygen gas
4. A solution contains both chloride ions (high concentration) and hydroxide ions. What is produced at the anode?
- A. Oxygen
- B. Chlorine
- C. Hydrogen
- D. Sodium
5. A student electrolyses a very dilute solution of potassium bromide. Based on competing-ion rules, what would you predict forms at each electrode, and why?
- A. Potassium at the cathode and bromine at the anode, because both ions are more abundant than water's ions
- B. Hydrogen at the cathode (potassium is more reactive) and bromine at the anode (bromide is more concentrated than hydroxide even when dilute)
- C. Hydrogen at the cathode (potassium is more reactive) and oxygen at the anode (in a very dilute solution, hydroxide is discharged over the sparse bromide)
- D. Potassium at the cathode and oxygen at the anode, since dilute solutions always favour oxygen