Chemistry-only: recognise acids and explain carbonate observations
| English | 中文 | Pinyin |
|---|---|---|
| carboxylic acid/ˌkɑːbəkˈsɪlɪk ˈæsɪd/ | 羧酸 | suō suān |
| carboxyl group/ˈkɑːbəksɪl ɡruːp/ | 羧基 | suō jī |
What would explain this observation?
- Ethanoic acid contains both C=O and O–H within one COOH group. Treating its OH as an ordinary alcohol group would predict the wrong family and reactions.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Carboxylic acids 羧酸 contain the –COOH functional group. The first four named members are methanoic acid HCOOH, ethanoic acid CH₃COOH, propanoic acid CH₃CH₂COOH and butanoic acid CH₃CH₂CH₂COOH. The carbon in COOH counts as part of the total carbon number. It has a double bond to one oxygen and a single bond to an O–H group. The individual displayed panels show every atom and bond.
- carboxylic acid: An organic acid containing the –COOH functional group; carboxyl group 羧基: The –COOH group containing C=O and O–H attached to the same carbon.
Which carbon must be counted when naming CH₃CH₂COOH?
These first-four acids dissolve in water to make acidic solutions. A suitable indicator or measured pH demonstrates acidity under the stated conditions. They react with carbonates to form a salt, carbon dioxide and water. For example, ethanoic acid with sodium carbonate forms sodium ethanoate plus the gas and water. Carbon dioxide can turn limewater milky in an approved product test. Reaction with alcohols forms an ester and water, developed in the separate ester lesson.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- These first-four acids dissolve in water to make acidic solutions. A suitable indicator or measured pH demonstrates acidity under the stated conditions. They react with carbonates to form a salt, carbon dioxide and water. For example, ethanoic acid with sodium carbonate forms sodium ethanoate plus the gas and water. Carbon dioxide can turn limewater milky in an approved product test. Reaction with alcohols forms an ester and water, developed in the separate ester lesson.
- Compare a supplied acid structure with the named member by counting all carbons, including COOH. For an approved supervised carbonate comparison, use teacher-selected dilute acids, comparable volumes and carbonate quantities, and record effervescence or gas measurements. Keep a path for gas to escape or reach the approved collector. Indicator colour identifies acidity, not the precise acid; different concentration or temperature can affect reaction rate.
Which two habits make the investigation or model in this case more defensible?
Compare a supplied acid structure with the named member by counting all carbons, including COOH. For an approved supervised carbonate comparison, use teacher-selected dilute acids, comparable volumes and carbonate quantities, and record effervescence or gas measurements. Keep a path for gas to escape or reach the approved collector. Indicator colour identifies acidity, not the precise acid; different concentration or temperature can affect reaction rate.
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: CH₃CH₂COOH has three C, six H and two O atoms, eleven altogether. The acid name is propanoic acid: the two-carbon CH₃CH₂ fragment is joined to a third carbon in COOH. Four represented molecules contain 4×11=44 atoms and eight oxygen atoms. Counting only CH₃CH₂ would give the wrong family member.
Two represented butanoic acid molecules each have formula C₄H₈O₂. Find their total oxygen atoms. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Two represented butanoic acid molecules each have formula C₄H₈O₂. Find their total oxygen atoms.
The result is 4 atoms. Known: CH₃CH₂COOH has three C, six H and two O atoms, eleven altogether. The acid name is propanoic acid: the two-carbon CH₃CH₂ fragment is joined to a third carbon in COOH. Four represented molecules contain 4×11=44 atoms and eight oxygen atoms. Counting only CH₃CH₂ would give the wrong family member.
Check the conclusion and its limits
- Do not omit the carboxyl carbon or require a balanced carbonate equation where the specification asks only for a description. Common-tier acidity and reaction observations remain separate from the Higher explanation of partial ionisation. A weak-acid description does not establish low concentration or safe handling, and acidity alone does not prove that an unknown is ethanoic acid.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
The OH within a carboxyl group makes every carboxylic acid an ordinary alcohol. This claim is false: Do not omit the carboxyl carbon or require a balanced carbonate equation where the specification asks only for a description. Common-tier acidity and reaction observations remain separate from the Higher explanation of partial ionisation. A weak-acid description does not establish low concentration or safe handling, and acidity alone does not prove that an unknown is ethanoic acid.
Chemistry-only: recognise acids and explain carbonate observations: These first-four acids dissolve in water to make acidic solutions. A suitable indicator or measured pH demonstrates acidity under the stated conditions. They react with carbonates to form a salt, carbon dioxide and water. For example, ethanoic acid with sodium carbonate forms sodium ethanoate plus the gas and water. Carbon dioxide can turn limewater milky in an approved product test. Reaction with alcohols forms an ester and water, developed in the separate ester lesson.
The OH within a carboxyl group makes every carboxylic acid an ordinary alcohol.
Do not omit the carboxyl carbon or require a balanced carbonate equation where the specification asks only for a description. Common-tier acidity and reaction observations remain separate from the Higher explanation of partial ionisation. A weak-acid description does not establish low concentration or safe handling, and acidity alone does not prove that an unknown is ethanoic acid.
An organic acid containing the –COOH functional group: write the technical term.
carboxylic acid means An organic acid containing the –COOH functional group.