12.5 Identification of Ions & Gases (Cambridge (CIE) O Level Chemistry): Flashcards
Exam code: 5070
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What reagent is used to test for sulfate ions?
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What reagent is used to test for sulfate ions?
To test for sulfate ions, the solution is acidified with dilute nitric acid and aqueous barium nitrate solution is added. A white precipitate of barium sulfate confirms the presence of SO42- ions.
To test for halide ions, the solution is acidified with dilute ______ acid and then aqueous silver nitrate is added. Bromide ions give a ______ precipitate.
To test for halide ions, the solution is acidified with dilute nitric acid and then aqueous silver nitrate is added. Bromide ions give a cream precipitate.
Why must dilute nitric acid rather than hydrochloric acid be used when testing for halide ions with silver nitrate?
Dilute nitric acid must be used because dilute hydrochloric acid would introduce chloride ions into the solution, producing a white precipitate even if no halide ions were originally present, giving a false positive result.
When dilute acid is added to a carbonate, the correct observation is ______, not just 'a gas is produced'.
When dilute acid is added to a carbonate, the correct observation is effervescence, not just 'a gas is produced'.
True or False?
Iodide ions produce a white precipitate when acidified silver nitrate solution is added.
False.
Iodide ions produce a yellow precipitate with acidified silver nitrate solution, whereas chloride ions produce a white precipitate and bromide ions produce a cream precipitate.
The sulfite ion (SO32-) is identified by adding acidified aqueous potassium manganate(VII), which changes colour from ______ to ______.
The sulfite ion (SO32-) is identified by adding acidified aqueous potassium manganate(VII), which changes colour from purple to colourless.
How are nitrate ions identified in solution?
Nitrate ions are identified by adding aqueous sodium hydroxide and aluminium foil to the solution and warming carefully. Ammonia gas is produced, which turns damp red litmus paper blue.
What is a flame test used to identify?
A flame test is used to identify metal cations by the characteristic colour they produce when placed in the blue flame of a Bunsen burner.
Iron(II) ions give a ______ precipitate with sodium hydroxide solution, while iron(III) ions give a ______ precipitate.
Iron(II) ions give a green precipitate with sodium hydroxide solution, while iron(III) ions give a red-brown precipitate.
How can aluminium ions be distinguished from zinc ions using sodium hydroxide and ammonia solutions?
Both aluminium and zinc ions form a white precipitate with sodium hydroxide solution, but only zinc hydroxide dissolves in excess ammonia solution, whereas aluminium hydroxide does not dissolve in excess ammonia.
In a flame test, sodium ions produce a ______ flame, while potassium ions produce a ______ flame.
In a flame test, sodium ions produce a yellow flame, while potassium ions produce a lilac flame.
True or False?
Calcium hydroxide precipitate dissolves when excess sodium hydroxide solution is added.
False.
Calcium hydroxide precipitate does not dissolve in excess sodium hydroxide solution, which distinguishes Ca2+ from Al3+ and Zn2+, whose hydroxides dissolve in excess NaOH.
Before a flame test, the wire loop must be cleaned by dipping it in concentrated acid and holding it in the Bunsen flame until there is no ______ change, to avoid ______.
Before a flame test, the wire loop must be cleaned by dipping it in concentrated acid and holding it in the Bunsen flame until there is no colour change, to avoid contamination.
How are ammonium ions identified using sodium hydroxide solution?
Ammonium ions are identified by adding sodium hydroxide solution to the test solution and warming the mixture. Ammonia gas is produced, which turns damp red litmus paper blue.
Copper(II) ions produce a ______ precipitate with sodium hydroxide solution, and this precipitate ______ in excess ammonia solution to give a dark blue solution.
Copper(II) ions produce a light blue precipitate with sodium hydroxide solution, and this precipitate dissolves in excess ammonia solution to give a dark blue solution.
What is the test for oxygen gas?
A glowing splint is held near the gas. If the splint relights, oxygen is present.
Hydrogen gas is tested by holding a ______ splint near it. A positive result is a ______ pop.
Hydrogen gas is tested by holding a lighted splint near it. A positive result is a squeaky pop.
How is ammonia gas identified in the laboratory?
Ammonia gas is identified by holding damp red litmus paper near it. The paper turns blue because ammonia is an alkaline gas.
Carbon dioxide is identified by bubbling the gas through ______, which turns ______ due to the formation of calcium carbonate.
Carbon dioxide is identified by bubbling the gas through limewater, which turns milky due to the formation of calcium carbonate.
True or False?
Chlorine gas turns damp litmus paper blue.
False.
Chlorine gas bleaches damp litmus paper, while it is ammonia gas that turns damp red litmus paper blue.
Sulfur dioxide gas is identified by adding acidified aqueous potassium manganate(VII), which changes colour from ______ to ______.
Sulfur dioxide gas is identified by adding acidified aqueous potassium manganate(VII), which changes colour from purple to colourless.
Why does hydrogen produce a squeaky pop when tested with a lighted splint?
Hydrogen produces a squeaky pop because it burns rapidly in air when ignited. The energy released from this rapid combustion causes a small explosion.
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