Chemistry-only: four observations for the first alcohols
הוצג| English | משמעות |
|---|---|
| solubility/ˌsɒljuːˈbɪlɪti/ | מסיסות |
| alcohol oxidation/ˈælkəhɒl ˌɒksɪˈdeɪʃn/ | חמצון של אלכוהול |
What would explain this observation?
- Ethanol burns to carbon dioxide and water, yet its reaction with sodium releases hydrogen. Naming the reagent prevents these two observations being confused.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- The first-four primary alcohols shown react with sodium to release hydrogen and form a sodium-containing organic product. They burn in sufficient oxygen to form carbon dioxide and water, releasing energy. They dissolve in water to form solutions, though solubility 溶解度 decreases along these examples and butanol dissolves to a more limited extent. With a suitable oxidising agent under appropriate heating, the shown primary alcohols can be oxidised to the corresponding carboxylic acids.
- alcohol oxidation 醇的氧化: Reaction of the stated alcohol with an oxidising agent under the given conditions; solubility: How much solute can dissolve in a stated amount of solvent under specified conditions.
Which statement is correct for the taught primary ethanol example?
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Ethanol reacts with sodium to release HYDROGEN (from the OH group), and burns completely to carbon dioxide and water. Neither reaction releases only carbon dioxide, and adding water changes nothing chemically.
Match each technical term to its precise meaning.
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Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- For the displayed primary examples, methanol can give methanoic acid, ethanol ethanoic acid, propanol propanoic acid and butanol butanoic acid. The OH carbon’s position matters; a different alcohol arrangement cannot automatically be assigned the same oxidation product. In an approved test, acidified potassium dichromate(VI) can change orange to green as it oxidises the primary alcohol. The acquired GCSE requirement asks for observations/descriptions, not aldehyde mechanisms or balanced equations for these non-combustion reactions.
- Record reagent, conditions and observation in separate columns. Describe solution formation with water as mixing/dissolving, not proof that water has made a new alcohol. Any sodium or oxidising-agent demonstration requires the school’s risk assessment, trained handling, eye protection and approved small quantities; chromium(VI) reagents need controlled waste. Students should analyse reference observations if the school does not approve the demonstration. Do not add sodium to an aqueous alcohol mixture to infer an alcohol-only reaction.
Which two habits make the investigation or model in this case more defensible?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
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: complete ethanol combustion is C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. Carbon count is 2, hydrogen 6 and oxygen 7 on each side; the fuel already contributes one O atom. Two ethanol molecules consume six O₂ molecules in this represented complete-combustion equation. Balancing methanol gives 2CH₃OH + 3O₂ → 2CO₂ + 4H₂O.
Complete ethanol combustion uses three O₂ per ethanol molecule. Find O₂ needed for four ethanol molecules. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Complete ethanol combustion uses three O₂ per ethanol molecule. Find O₂ needed for four ethanol molecules.
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The result is 12 molecules. Known: each ethanol molecule uses 3 O2 for complete combustion. For four ethanol molecules: 4 x 3 = 12 O2 molecules. The oxygen atom inside each ethanol molecule counts towards the balance.
Check the conclusion and its limits
- Do not forget the oxygen already in the alcohol when balancing combustion, or call the hydrogen from sodium reaction carbon dioxide. Methanol and other alcohols can be toxic and flammable; miscibility does not establish safety. A written response or a supplied colour change does not certify completion of an actual school practical.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Balanced combustion must ignore the oxygen atom already present in ethanol. This claim is false: Ethanol's formula C2H5OH already contains an oxygen atom, so the oxygen balance reads 1 + 6 = 7 on each side of C2H5OH + 3O2 -> 2CO2 + 3H2O. Ignoring the fuel's own oxygen unbalances the equation.
Chemistry-only: four observations for the first alcohols: For the displayed primary examples, methanol can give methanoic acid, ethanol ethanoic acid, propanol propanoic acid and butanol butanoic acid. The OH carbon’s position matters; a different alcohol arrangement cannot automatically be assigned the same oxidation product. In an approved test, acidified potassium dichromate(VI) can change orange to green as it oxidises the primary alcohol. The acquired GCSE requirement asks for observations/descriptions, not aldehyde mechanisms or balanced equations for these non-combustion reactions.
Balanced combustion must ignore the oxygen atom already present in ethanol.
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Ethanol's formula C2H5OH already contains an oxygen atom, so the oxygen balance reads 1 + 6 = 7 on each side of C2H5OH + 3O2 -> 2CO2 + 3H2O. Ignoring the fuel's own oxygen unbalances the equation.
Reaction of the stated alcohol with an oxidising agent under the given conditions: write the technical term.
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alcohol oxidation means Reaction of the stated alcohol with an oxidising agent under the given conditions.