Chemistry-only: variable ions, colours and catalysts
| English | Français |
|---|---|
| catalyst/ˈkætəlɪst/ | catalyst · catalyseur |
| variable charge/ˈveərɪəbl tʃɑːdʒ/ | variable charge |
What would explain this observation?
- Iron forms Fe²⁺ and Fe³⁺ ions in different compounds. A charge must therefore be specified; knowing only that a substance contains iron cannot determine its complete formula.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Many transition metals form ions with different charges, coloured compounds and useful catalysts 催化剂. Iron(II) and iron(III) show variable charges 可变电荷. Copper(II) aqueous compounds are commonly blue; iron(II) solutions are often pale green and iron(III) solutions yellow/brown. Chromium(III) compounds can be green, manganate(VII) is purple, hydrated cobalt(II) compounds can be pink and nickel(II) solutions commonly green. Colour depends on the particular compound, hydration and conditions.
- catalyst: A substance increasing reaction rate by a lower-activation pathway without being used up overall; variable charge: The ability of an element to form ions with different charges in different compounds.
Why must iron’s charge be specified when forming a chloride formula?
Catalysts increase reaction rate without being used up overall. Iron catalyses the Haber process; nickel is used in hydrogenation; manganese dioxide catalyses hydrogen peroxide decomposition. A catalyst changes the route and rate, not the balanced reaction’s overall atom count. Variable charges require matching negative-ion charge: FeCl₂ contains Fe²⁺ and FeCl₃ contains Fe³⁺ with Cl⁻ in each case.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Catalysts increase reaction rate without being used up overall. Iron catalyses the Haber process; nickel is used in hydrogenation; manganese dioxide catalyses hydrogen peroxide decomposition. A catalyst changes the route and rate, not the balanced reaction’s overall atom count. Variable charges require matching negative-ion charge: FeCl₂ contains Fe²⁺ and FeCl₃ contains Fe³⁺ with Cl⁻ in each case.
- Use labelled compound photographs, supplied solution observations and given ion charges. Compare an actual teacher-supervised catalysed reaction with an uncatalysed control, maintaining temperature, concentration and volume. Cobalt/nickel compounds and strong oxidizers require approved handling and disposal; reference evidence is appropriate when they are not used in a school experiment. Do not identify an unknown compound solely from colour.
Which two habits make the investigation or model in this case more defensible?
Use labelled compound photographs, supplied solution observations and given ion charges. Compare an actual teacher-supervised catalysed reaction with an uncatalysed control, maintaining temperature, concentration and volume. Cobalt/nickel compounds and strong oxidizers require approved handling and disposal; reference evidence is appropriate when they are not used in a school experiment. Do not identify an unknown compound solely from colour.
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: a compound contains Fe³⁺ and O²⁻. Two Fe³⁺ supply total +6 and three O²⁻ supply −6, giving neutral Fe₂O₃. With Fe²⁺, one iron ion and one oxide ion balance as FeO. The different iron charges produce different ratios; neither formula is inferred merely from a brown or black appearance.
How many Cl⁻ ions balance the charge of two Fe³⁺ ions? Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
How many Cl⁻ ions balance the charge of two Fe³⁺ ions?
The result is 6 ions. Known: a compound contains Fe³⁺ and O²⁻. Two Fe³⁺ supply total +6 and three O²⁻ supply −6, giving neutral Fe₂O₃. With Fe²⁺, one iron ion and one oxide ion balance as FeO. The different iron charges produce different ratios; neither formula is inferred merely from a brown or black appearance.
Check the conclusion and its limits
- Many does not mean every transition compound is coloured or every metal has every charge. A catalyst may take part in intermediate steps while being regenerated overall. Its presence does not increase the theoretical amount of product from a fixed limiting reactant or prove an equilibrium composition has changed.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A catalyst is permanently consumed in the overall reaction. This claim is false: Many does not mean every transition compound is coloured or every metal has every charge. A catalyst may take part in intermediate steps while being regenerated overall. Its presence does not increase the theoretical amount of product from a fixed limiting reactant or prove an equilibrium composition has changed.
Chemistry-only: variable ions, colours and catalysts: Catalysts increase reaction rate without being used up overall. Iron catalyses the Haber process; nickel is used in hydrogenation; manganese dioxide catalyses hydrogen peroxide decomposition. A catalyst changes the route and rate, not the balanced reaction’s overall atom count. Variable charges require matching negative-ion charge: FeCl₂ contains Fe²⁺ and FeCl₃ contains Fe³⁺ with Cl⁻ in each case.
A catalyst is permanently consumed in the overall reaction.
Many does not mean every transition compound is coloured or every metal has every charge. A catalyst may take part in intermediate steps while being regenerated overall. Its presence does not increase the theoretical amount of product from a fixed limiting reactant or prove an equilibrium composition has changed.
A substance increasing reaction rate by a lower-activation pathway without being used up overall: write the technical term.
catalyst means A substance increasing reaction rate by a lower-activation pathway without being used up overall.