Chemistry • Year 12 • Module 6 • Lesson 2
Nomenclature, Indicators & Predicting Acid Reactions
Lock in the naming rules for binary and oxoacids, the three indicator ranges, and the four acid reaction patterns before tackling calculation lessons.
1. Term–definition match
The twelve definitions below are shuffled. Write the matching term from this list in the right-hand column: binary acid, oxoacid, neutralisation, indicator, hydrochloric acid, sulfuric acid, nitric acid, acetic (ethanoic) acid, phosphoric acid, acid-carbonate reaction, acid-metal reaction, Le Chatelier’s Principle. 12 marks
| # | Definition | Matching term |
|---|---|---|
| 1.1 | An acid that contains hydrogen bonded to a single non-metal with no oxygen present; named using the hydro-/ic pattern. | |
| 1.2 | An acid that contains hydrogen, oxygen and another element; named from the polyatomic ion it contains. | |
| 1.3 | The reaction between an acid and a base producing a salt and water; formula HCl + NaOH → NaCl + H&sub2;O is an example. | |
| 1.4 | A weak acid (HIn) whose conjugate base (In¹−) is a different colour; changes colour at a characteristic pH range by responding to [H¹+] via equilibrium shift. | |
| 1.5 | Formula HCl; strong binary acid formed by dissolving hydrogen chloride gas in water; used in Orica’s industrial cleaning processes. | |
| 1.6 | Formula H&sub2;SO&sub4;; diprotic strong oxoacid from the sulfate ion; used in lead-acid batteries in Australian mining vehicles. | |
| 1.7 | Formula HNO&sub3;; strong oxoacid from the nitrate ion; raw material for Orica’s ammonium nitrate fertiliser at Kooragang Island. | |
| 1.8 | Formula CH&sub3;COOH; weak organic acid naturally present in Australian citrus juice and vinegar; responsible for the sourness of Mildura lemons. | |
| 1.9 | Formula H&sub3;PO&sub4;; weak oxoacid from the phosphate ion; produced in large quantities for phosphate fertilisers. | |
| 1.10 | Reaction producing a salt, water and CO&sub2;(g); the gas is produced because carbonic acid (H&sub2;CO&sub3;) decomposes immediately to H&sub2;O + CO&sub2;. | |
| 1.11 | Reaction between an acid and an active metal above hydrogen in the activity series; produces a salt and H&sub2;(g). | |
| 1.12 | The principle that when a system at equilibrium is disturbed, it responds to partially oppose the disturbance; used to explain why indicator colour changes when [H¹+] changes. |
2. True or false — with correction
For each statement, circle T or F. If false, write the corrected version on the line below. 10 marks (1 T/F + 1 correction where needed)
2.1 H&sub2;SO&sub4; should be named “hydrosulfuric acid” because it contains hydrogen and sulfur. T / F
2.2 HF is a weak acid despite following the binary acid naming pattern because the H–F bond is unusually short and strong. T / F
2.3 Phenolphthalein turns pink in any solution with pH below 8.3 because it is a pink dye. T / F
2.4 When acid reacts with a carbonate, the three products are always a salt, water and CO&sub2;(g). T / F
2.5 Copper metal dissolves readily in dilute hydrochloric acid to produce copper chloride and hydrogen gas. T / F
3. Fill-in-the-blank — indicator equilibrium
Complete the paragraph below using the words from this word bank. Each word is used once. 8 marks
Word bank: Le Chatelier’s Principle • HIn • In¹− • left • right • acid • base • pKa
An indicator is a weak acid in which the acid form is written as (1) _____________ and its conjugate base form is written as (2) _____________. The two forms are different colours, so the overall colour of the solution depends on which form dominates. By (3) _____________, adding H¹+ to the indicator equilibrium HIn ⇌ H¹+ + In¹− pushes the equilibrium to the (4) _____________, increasing the concentration of the (5) _____________ form. Conversely, in a basic solution where OHˉ removes H¹+, the equilibrium shifts to the (6) _____________, and the (7) _____________ form dominates. The transition between the two colours occurs over a range of approximately (8) _____________ ± 1 pH units.
4. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 Why is the prefix “hydro-” never applied to oxoacids?
4.2 What is the function of H&sub2;CO&sub3; (carbonic acid) in the acid–carbonate reaction, and why does it immediately decompose?
4.3 Why must the metal be above hydrogen in the activity series for an acid–metal reaction to produce H&sub2;(g)?
4.4 NaOH, KOH, Ca(OH)&sub2; and Ba(OH)&sub2; are all strong bases. What distinguishes NH&sub3; as a base from these four, and how should the correct ionic equation for dissolved NH&sub3; be written?
5. Concept map — acid reaction patterns
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a short linking phrase (e.g. “reacts with”, “produces”, “is identified by”). Aim for at least 5 labelled arrows. 5 marks
Supplied terms: acid • carbonate/hydrogen carbonate • reactive metal • base (hydroxide) • CO&sub2; gas • salt + water.
Q1 — Term–definition matches
1.1 binary acid • 1.2 oxoacid • 1.3 neutralisation • 1.4 indicator • 1.5 hydrochloric acid • 1.6 sulfuric acid • 1.7 nitric acid • 1.8 acetic (ethanoic) acid • 1.9 phosphoric acid • 1.10 acid-carbonate reaction • 1.11 acid-metal reaction • 1.12 Le Chatelier’s Principle.
Q2 — True or false with correction
2.1 False. H&sub2;SO&sub4; contains oxygen, so it is an oxoacid. “Hydro-” is only used for binary acids (no oxygen). The correct name is sulfuric acid, from the sulfate ion (SO&sub4;²−, ending –ate → –ic acid). Hydrosulfuric acid is the name of H&sub2;S.
2.2 True. HF is weak because the H–F bond is very short and strong (fluorine has the smallest atomic radius of the halogens), making proton donation energetically difficult despite fluorine’s high electronegativity.
2.3 False. Phenolphthalein is an acid–base indicator, not a simple pink dye. Below pH 8.3 the HIn form dominates and the solution is colourless. The pink colour (In¹− form) only appears between pH 8.3 and 10.0 (its transition range).
2.4 True. All three products (salt + H&sub2;O + CO&sub2;) must be included in any balanced equation for an acid–carbonate or acid–hydrogen carbonate reaction.
2.5 False. Copper is below hydrogen in the activity series, so it does not react with dilute HCl by the standard acid–metal (Pattern 3) mechanism. No reaction occurs under these conditions.
Q3 — Cloze answers
(1) HIn • (2) In¹− • (3) Le Chatelier’s Principle • (4) left • (5) acid • (6) right • (7) base • (8) pKa.
Q4.1 — “Hydro-” prefix and oxoacids
“Hydro-” is reserved as a structural signal meaning “contains hydrogen bonded directly to a non-metal with no oxygen.” Oxoacids already contain oxygen, so applying “hydro-” to them would be chemically misleading and violates the IUPAC naming convention that names oxoacids from their parent polyatomic ion (–ate → –ic acid; –ite → –ous acid).
Q4.2 — Role of H&sub2;CO&sub3;
When an acid reacts with a carbonate, H¹+ first combines with CO&sub3;²− to form carbonic acid (H&sub2;CO&sub3;) as an intermediate. H&sub2;CO&sub3; is thermodynamically unstable and immediately decomposes: H&sub2;CO&sub3; → H&sub2;O + CO&sub2;(g). The observed bubbling in these reactions is the CO&sub2; escaping. All three products (salt, water, CO&sub2;) must appear in a balanced equation.
Q4.3 — Activity series and H&sub2; production
For H&sub2;(g) to be produced, the metal must be capable of displacing hydrogen from the acid. Only metals higher in the activity series than hydrogen (e.g. Mg, Al, Zn, Fe) are strong enough reducing agents to do this. Metals below hydrogen (Cu, Ag, Au) cannot reduce H¹+ to H&sub2; under standard conditions.
Q4.4 — NH&sub3; as a Brønsted-Lowry base
NaOH, KOH, Ca(OH)&sub2; and Ba(OH)&sub2; are Arrhenius bases that release OH¹− directly on dissociation. NH&sub3; is a Brønsted-Lowry base that accepts a proton from water: NH&sub3; + H&sub2;O ⇌ NH&sub4;¹+ + OH¹−. NH&sub3; is weak because this equilibrium lies far to the left (only partial proton acceptance). Writing “NH&sub4;OH → NH&sub4;¹+ + OH¹−” is incorrect — NH&sub4;OH is not a significant species in solution.
Q5 — Concept map (sample)
Valid arrows include: acid ⟶ reacts with base → salt + water; acid ⟶ reacts with carbonate/H-carbonate → salt + water + CO&sub2; gas; acid ⟶ reacts with reactive metal → salt + H&sub2; gas (H&sub2; not listed as a chip but salt + water chip is the salt component). Any chemically valid linking phrases are accepted. Award 1 mark per correctly labelled, directionally accurate arrow, up to 5 marks.