Molten binary compounds: metal at the cathode, non-metal at the anode
| English | 中文 | Pinyin |
|---|---|---|
| binary ionic compound | 二元离子化合物 | èr yuán lí zi huà hé wù |
| molten electrolyte | 熔融电解质 | róng róng diàn jiě zhì |
What would explain this observation?
- Molten sodium chloride and sodium chloride dissolved in water do not give the same cathode product. The molten compound has no competing water-derived hydrogen ions.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- A binary ionic compound 二元离子化合物 contains two elements. When its melt is electrolysed with inert electrodes, its metal forms at the negative cathode and its non-metal at the positive anode. Molten lead bromide gives lead and bromine; molten sodium chloride gives sodium and chlorine. Ions must be free to move, so the solid form is not the conducting electrolyte in this model.
- molten electrolyte 熔融电解质: A melted ionic compound whose ions can move; binary ionic compound: An ionic compound containing two elements.
What forms at the cathode from molten lead bromide with inert electrodes?
Identify the positive metal ion and negative non-metal ion from the formula. The cathode product is the metal element, while a halogen anode product is diatomic, such as Br₂ or Cl₂. Do not write bromide as the elemental product. The formula’s ratio is determined by charge, and the product equation must preserve every atom.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Identify the positive metal ion and negative non-metal ion from the formula. The cathode product is the metal element, while a halogen anode product is diatomic, such as Br₂ or Cl₂. Do not write bromide as the elemental product. The formula’s ratio is determined by charge, and the product equation must preserve every atom.
- Use diagrams, acquired observations or a teacher-approved demonstration rather than prescribing independent molten lead bromide work. The specification names anhydrous zinc chloride as a safer alternative, but it still needs an approved risk assessment and heated apparatus. Hot corrosive melts and toxic gas products cannot be treated like an ordinary room-temperature salt solution.
Which two habits make the investigation or model in this case more defensible?
Use diagrams, acquired observations or a teacher-approved demonstration rather than prescribing independent molten lead bromide work. The specification names anhydrous zinc chloride as a safer alternative, but it still needs an approved risk assessment and heated apparatus. Hot corrosive melts and toxic gas products cannot be treated like an ordinary room-temperature salt solution.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: ZnCl₂ contains one Zn²⁺ for two Cl⁻ ions. Its overall decomposition is ZnCl₂ → Zn + Cl₂. Six represented formula units can give six zinc atoms and six chlorine molecules, containing twelve chlorine atoms. This equation is common-tier product accounting; the electron half equations are taught separately at Higher Tier.
In ZnCl₂ → Zn + Cl₂, how many chlorine atoms are contained in the products from eight represented ZnCl₂ formula units? Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
In ZnCl₂ → Zn + Cl₂, how many chlorine atoms are contained in the products from eight represented ZnCl₂ formula units?
The result is 16 atoms. Known: ZnCl₂ contains one Zn²⁺ for two Cl⁻ ions. Its overall decomposition is ZnCl₂ → Zn + Cl₂. Six represented formula units can give six zinc atoms and six chlorine molecules, containing twelve chlorine atoms. This equation is common-tier product accounting; the electron half equations are taught separately at Higher Tier.
Check the conclusion and its limits
- Molten is not the same as aqueous. Water changes the available species and product rules. Inert means the electrode is not intended to take part in the stated reaction, not that every material survives all conditions. Products need both the element name and the correct electrode.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Molten and aqueous sodium chloride necessarily produce the same cathode element. This claim is false: Molten is not the same as aqueous. Water changes the available species and product rules. Inert means the electrode is not intended to take part in the stated reaction, not that every material survives all conditions. Products need both the element name and the correct electrode.
Molten binary compounds: metal at the cathode, non-metal at the anode: Identify the positive metal ion and negative non-metal ion from the formula. The cathode product is the metal element, while a halogen anode product is diatomic, such as Br₂ or Cl₂. Do not write bromide as the elemental product. The formula’s ratio is determined by charge, and the product equation must preserve every atom.
Molten and aqueous sodium chloride necessarily produce the same cathode element.
Molten is not the same as aqueous. Water changes the available species and product rules. Inert means the electrode is not intended to take part in the stated reaction, not that every material survives all conditions. Products need both the element name and the correct electrode.
A melted ionic compound whose ions can move: write the technical term.
molten electrolyte means A melted ionic compound whose ions can move.