Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine - AQA - A-Level Chemistry - Question 4 - 2021 - Paper 3
Question 4
Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine.
Equation
Observation
A solution that is thought to cont... show full transcript
Worked Solution & Example Answer:Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine - AQA - A-Level Chemistry - Question 4 - 2021 - Paper 3
Step 1
Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine.
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Answer
The equation for the reaction is:
2NaBr+H2​SO4​→Na2​SO4​+2HBr+Br2​
Here, sodium bromide reacts with concentrated sulfuric acid to produce sodium sulfate, hydrogen bromide, and bromine gas.
Step 2
State one observation made during this reaction.
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Answer
During the reaction, orange/brown fumes of bromine are observed, indicating the formation of bromine gas.
Step 3
Give a reason for the use of each reagent.
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Answer
Dilute nitric acid is used to remove any unwanted ions that may interfere with the subsequent tests for halides.
Aqueous silver nitrate is added to precipitate chloride and iodide ions as silver chloride and silver iodide, respectively. This is crucial for identifying halides in the solution.
A dilute solution of ammonia is added to distinguish between silver chloride and silver iodide; silver chloride dissolves in ammonia, while silver iodide does not.
Step 4
Explain the observations.
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The formation of a pale yellow precipitate indicates the presence of silver iodide, which is less soluble and precipitates in the presence of iodide ions. The excess ammonia dissolves the silver chloride precipitate, confirming its identity as it reacts to form a soluble silver ammine complex while leaving the silver iodide intact.
Step 5
Give ionic equations for any reactions.
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Answer
The reaction of chloride ions with silver nitrate can be represented as:
Ag+(aq)+Cl−(aq)→AgCl(s)
In the presence of ammonia, the dissolution of silver chloride can be expressed as:
