9701 · 11.3
Some reactions of the halide ions flashcards
Revision flashcards for Cambridge 9701 Some reactions of the halide ions (syllabus 11.3). Flip, recall, then mark a real past-paper question.
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What is the colour of the precipitate formed when aqueous silver nitrate is added to a solution containing chloride ions, Cl⁻?
A white precipitate of silver chloride (AgCl).
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What is the colour of the precipitate formed when aqueous silver nitrate is added to a solution containing bromide ions, Br⁻?
A cream precipitate of silver bromide (AgBr).
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What is the colour of the precipitate formed when aqueous silver nitrate is added to a solution containing iodide ions, I⁻?
A yellow precipitate of silver iodide (AgI).
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How does the solubility of silver chloride (AgCl) in ammonia compare to silver iodide (AgI)?
AgCl is soluble in dilute aqueous ammonia, forming the complex ion [Ag(NH₃)₂]⁺. AgI is insoluble in even concentrated aqueous ammonia.
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Why is dilute nitric acid added before silver nitrate in the test for halide ions?
To acidify the solution and react with any carbonate ions (CO₃²⁻) present, which would otherwise form a white precipitate of silver carbonate (Ag₂CO₃) and give a false positive result.
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What are the products when solid sodium chloride reacts with concentrated sulfuric acid?
Sodium hydrogensulfate (NaHSO₄) and hydrogen chloride gas (HCl). This is an acid-base reaction, not a redox reaction.
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What are the main products when solid sodium bromide reacts with concentrated sulfuric acid?
HBr gas (misty fumes), Br₂ (brown fumes), and SO₂ gas (choking smell). The Br⁻ ion is a strong enough reducing agent to reduce H₂SO₄.
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Name three reduction products of sulfuric acid formed when it reacts with solid sodium iodide.
Sulfur dioxide (SO₂), elemental sulfur (S, a yellow solid), and hydrogen sulfide (H₂S, a gas with a 'bad egg' smell).
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Explain the trend in reducing power of the halide ions down Group 17.
Reducing power increases down the group (I⁻ > Br⁻ > Cl⁻). The ionic radius increases and there is more electron shielding, so the outermost electron is held less strongly by the nucleus and is more easily lost (oxidised).
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Complete the ionic equation: $Cl_2(aq) + 2I^-(aq) \rightarrow$ ?
$Cl_2(aq) + 2I^-(aq) \rightarrow 2Cl^-(aq) + I_2(aq)$. Chlorine is a stronger oxidising agent than iodine, so it displaces iodide ions from solution.
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What is observed when aqueous bromine is added to aqueous potassium iodide?
The solution turns from colourless (or pale orange if Br₂ is concentrated) to brown/black due to the formation of iodine (I₂).