Acids and bases
Introduced| English | Meaning |
|---|---|
| proton donor/ˈprəʊtɒn ˈdəʊnə/ | A species that transfers a hydrogen ion to another species in an acid-base reaction. |
| proton acceptor/ˈprəʊtɒn əkˈseptə/ | A species that takes a hydrogen ion from another species in an acid-base reaction. |
| alkali/ˈælkəlaɪ/ | alkali |
| conjugate/ˈkɒndʒuːɡeɪt/ | Describing an acid and base that differ by one proton. |
Donors and acceptors
- The Brønsted–Lowry theory defines acids and bases by what they do with protons.
- A proton is simply an $\text{H}^{+}$ ion.
- Every acid–base reaction transfers a proton.
A proton, in this context, is:
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A hydrogen ion (H⁺) is just a proton, which is what acids donate and bases accept.
A Brønsted–Lowry acid is a proton (H⁺) ______.
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A base is a proton acceptor.
Proton donors 质子供体 and acceptors
- an acid is a proton donor (it gives away $\text{H}^{+}$).
- a base is a proton acceptor 质子受体 (it takes $\text{H}^{+}$). A base that dissolves in water is an alkali 碱.
- When an acid gives a proton to a base, you get two conjugate 共轭 acid–base pairs.
Bronsted-Lowry: an acid donates a proton to a base, forming two conjugate pairs
The pH scale
Slide the pH or tap a substance — each step down in pH means ten times more H⁺ ions; acids are below 7, alkalis above.
In the Brønsted–Lowry theory, an acid is a:
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A Brønsted–Lowry acid donates a proton (H⁺); a base accepts one.
When an acid donates a proton to a base, the result is:
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The acid becomes its conjugate base and the base becomes its conjugate acid — two pairs.
Common ones to know
- Acids: $\text{HCl}$, $\text{H}_2\text{SO}_4$, $\text{HNO}_3$, ethanoic acid ($\text{CH}_3\text{COOH}$).
- Alkalis: $\text{NaOH}$, $\text{KOH}$, ammonia ($\text{NH}_3$).
Which is an alkali (a soluble base)?
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NaOH, KOH and NH₃ are alkalis; HCl, H₂SO₄, HNO₃ and CH₃COOH are acids.
Match each acid-base term to its meaning.
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Each item links the term to its correct meaning.
Conjugate pairs
- When an acid donates a proton it forms its conjugate base.
- HCl → Cl⁻ + H⁺: HCl and Cl⁻ are a conjugate acid–base pair.
You've got it
- a proton is an $\text{H}^{+}$ ion
- acid = proton donor; base = proton acceptor; a soluble base is an alkali
- proton transfer makes two conjugate acid–base pairs
- acids: HCl, H₂SO₄, HNO₃, CH₃COOH; alkalis: NaOH, KOH, NH₃