O-LevelChemistryAcids, Bases & Salts5070/21 · May/June 2019 · Q710 Marks
Ammonium carbonate, (NH₄)₂CO₃, is a white solid which decomposes when heated. (NH₄)₂CO₃(s) ⇌ 2NH₃(g) + CO₂(g) + H₂O(g)
- (a)A small sample of ammonium carbonate is heated in a test-tube. Describe how you will know when all the ammonium carbonate has decomposed.[1]
- (b)Calculate the total volume of ammonia and carbon dioxide, measured at room temperature and pressure, formed when 4.80g of ammonium carbonate is completely decomposed.[3]
- (c)Describe a chemical test for the ammonium ion. test observation[2]
- (d)Aqueous ammonium carbonate reacts with dilute hydrochloric acid. Construct the ionic equation, including state symbols, for this reaction.[2]
- (e)Solid ammonium carbonate does not conduct electricity. Aqueous ammonium carbonate conducts electricity. Explain these two observations.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.
- [1] solid disappears / ammonium carbonate disappears / nothing left in tube (1)
- [3] moles of ammonium carbonate = 4.80 /96 OR 0.05(00) (1)
- [3] moles of gas = 3 × 0.05 OR 0.15 (1)
- [3] volume of gas = (0.15 × 24) = 3.6 dm³ OR 3600 cm³ (1)
- [2] heat or warm with (aqueous) sodium hydroxide (1)
- [2] gas that turns (moist red) litmus blue (1)
- [2] CO₃²⁻(aq) + 2H⁺(aq) → CO₂(g) + H₂O(l)
- [2] correct formulae (1)
- [2] correct state symbols – dependent on correct formulae (1)
- [2] in solid ions cannot move (1)
- [2] in aqueous solution ions can move (1)
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →