Use a copy of the Periodic Table where you need one.
Which set of aqueous solutions will form only a colourless solution when mixed together in the same conical flask?
Source: 2020 SJI Year 3 End-of-Year P1 Q21
Which statement about the reaction between ammonium carbonate and dilute hydrochloric acid is false?
Source: 2024 CHIJ Prelim P1 Q13
Which reagent could be used to distinguish between dilute sulfuric acid and dilute hydrochloric acid?
Source: 2024 CHIJ Prelim P1 Q19
Aqueous ammonium sulfate is warmed with an excess of aqueous sodium hydroxide. The resulting mixture is neutralised with dilute nitric acid. The mixture is then mixed with aqueous barium nitrate. The precipitate is filtered off and the filtrate is evaporated to leave a white solid. What could the white solid be?
Source: 2024 SJI Prelim P1 Q18
A white solid reacted with dilute hydrochloric acid to form a colourless solution and a gas.
Test 1: with aqueous silver nitrate, the colourless solution gave a white precipitate.
Test 2: with aqueous ammonia in excess, the colourless solution gave a colourless solution.
Test 3: the gas formed a white precipitate when bubbled into aqueous calcium hydroxide.
What is the white solid?
Source: 2024 SJI Prelim P1 Q19
A powdered mixture of compound A and metal B is tested. The results are shown in the table.
| test | observation |
|---|---|
| 1 The mixture is mixed with excess dilute hydrochloric acid. | Gas D, which gives a white precipitate with limewater, is given off. Colourless solution C forms, and metal B is left. |
| 2 The mixture is filtered. A few drops of aqueous sodium hydroxide are added to solution C. | White precipitate E forms. |
| 3 Excess aqueous sodium hydroxide is added. | The white precipitate is insoluble. |
| 4 Metal B is heated strongly in oxygen to form metal oxide F. F is added to dilute sulfuric acid. | Blue solution G forms. |
Source: 2024 CHS Sec 3 End-of-Year Section B Q8 (adapted)
Mixture S contains one cation and two anions. A series of tests was performed on mixture S. The results are shown in the table.
| test | observation |
|---|---|
| 1 Dilute hydrochloric acid is added to mixture S. | Gas U is given off and solution T forms. Gas U gives a white precipitate in limewater. |
| 2 Aqueous sodium hydroxide is added to solution T. | Green precipitate V forms. It turns red-brown on standing. |
| 3 The mixture from test 2 is warmed with a piece of aluminium foil. | A gas is given off which turns moist red litmus paper blue. |
| 4 Acidified silver nitrate is added to solution T. | White precipitate W forms. |
Source: 2023 PRSS Prelim P2 A3 (adapted)
Ammonium-based fertilisers are made from ammonia.
Source: 2021 SJI Prelim P2 A2(a)(ii)
DKNO3, NaOH, Na2SO4[1]
A gives a red-brown precipitate of iron(III) hydroxide, B gives a white precipitate of barium sulfate, and C is blue because of the copper(II) ions.
BAmmonia gas is produced.[1]
The acid reacts with the carbonate to give carbon dioxide, which is acidic. Ammonia is given off by ammonium salts with an alkali, not with an acid.
Abarium nitrate solution[1]
Barium nitrate gives a white precipitate of barium sulfate with sulfuric acid only. The other reagents give the same result with both acids.
Dsodium nitrate[1]
Warming with sodium hydroxide drives off the ammonium ions as ammonia. Barium sulfate is filtered off, leaving sodium and nitrate ions in the filtrate.
Czinc carbonate[1]
The gas is carbon dioxide, so the solid is a carbonate. The hydroxide dissolves in excess aqueous ammonia, so the cation is zinc. The chloride in test 1 comes from the hydrochloric acid.
A: calcium carbonate, CaCO3 [1]
C: calcium chloride, CaCl2 [1]
D: carbon dioxide, CO2 [1]
E: calcium hydroxide, Ca(OH)2 [1]
Ca2+(aq) + 2OH−(aq) → Ca(OH)2(s) [1]
Aqueous barium nitrate: no observable change. [1]
Aqueous silver nitrate: a white precipitate forms. [1]
T: iron(II) chloride [1]
U: carbon dioxide [1]
V: iron(II) hydroxide [1]
W: silver chloride [1]
Iron(II), carbonate and nitrate ions (all three needed). Chloride is not accepted, as it could have come from the hydrochloric acid. [1]
Any one, e.g. CO2 + Ca(OH)2 → CaCO3 + H2O or Fe2+(aq) + 2OH−(aq) → Fe(OH)2(s) [1]
Calcium hydroxide reacts with ammonium-based fertilisers to form ammonia gas, which escapes into the atmosphere. [1]
This results in the loss of nitrogen from the fertiliser, which plants need for growth. [1]