Chemistry-only: acidified silver nitrate distinguishes three halides
| English | 中文 | Pinyin |
|---|---|---|
| halide test | 卤离子检验 | lǔ lí zi jiǎn yàn |
| silver halide | 卤化银 | lǔ huà yín |
What would explain this observation?
- Three pale precipitates look similar until they are compared side by side. The acid and precipitating reagent must be correct before a colour can identify the halide.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Halide ions in solution form precipitates with silver nitrate in the presence of dilute nitric acid. Chloride gives white silver chloride, bromide cream silver bromide and iodide yellow silver iodide. State the reagent sequence and observation together: acidify with dilute nitric acid, add silver nitrate, then record the precipitate colour. The solution-ion test differs from damp-litmus bleaching by chlorine gas.
- halide test 卤离子检验: The stated dilute-nitric-acid and silver-nitrate precipitation test for halide ions; silver halide 卤化银: The insoluble silver compound formed with the stated chloride, bromide or iodide ion.
Which reagent pair belongs to the halide test?
Nitric acid does not introduce a halide ion that would contaminate this test. Using hydrochloric acid instead introduces chloride and can produce a misleading white precipitate with silver nitrate. Acidification also removes carbonate interference in the standard comparison. The school method governs quantities and handling. Silver-halide colours are subtle, so compare known results side by side under the same light rather than relying on a tiny colour difference from memory.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Nitric acid does not introduce a halide ion that would contaminate this test. Using hydrochloric acid instead introduces chloride and can produce a misleading white precipitate with silver nitrate. Acidification also removes carbonate interference in the standard comparison. The school method governs quantities and handling. Silver-halide colours are subtle, so compare known results side by side under the same light rather than relying on a tiny colour difference from memory.
- Use a fresh clean portion of each solution, selected dilute nitric acid and approved silver nitrate under school supervision. Keep pipettes separate and record observations before assigning identities. Silver salts and acids require the current risk assessment, eye protection and controlled waste collection. Do not mix every reagent into the same unknown tube; previous tests may introduce ions that affect the next test. Additional ammonia-solubility chemistry is not required by this section.
Which two habits make the investigation or model in this case more defensible?
Use a fresh clean portion of each solution, selected dilute nitric acid and approved silver nitrate under school supervision. Keep pipettes separate and record observations before assigning identities. Silver salts and acids require the current risk assessment, eye protection and controlled waste collection. Do not mix every reagent into the same unknown tube; previous tests may introduce ions that affect the next test. Additional ammonia-solubility chemistry is not required by this section.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: NaBr + AgNO₃ → AgBr + NaNO₃ illustrates a one-to-one particle ratio for the precipitate. The supplied observation is cream, identifying bromide within the reference set. Four NaBr formula units reacting completely with the stated four AgNO₃ units give four AgBr units. These counts explain conservation; they do not turn colour into a measured concentration.
Five NaI formula units react one-to-one with silver nitrate. Count AgI units formed in the stated model. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Five NaI formula units react one-to-one with silver nitrate. Count AgI units formed in the stated model.
The result is 5 units. Known: NaBr + AgNO₃ → AgBr + NaNO₃ illustrates a one-to-one particle ratio for the precipitate. The supplied observation is cream, identifying bromide within the reference set. Four NaBr formula units reacting completely with the stated four AgNO₃ units give four AgBr units. These counts explain conservation; they do not turn colour into a measured concentration.
Check the conclusion and its limits
- Do not say chloride gives a yellow precipitate, replace nitric acid with hydrochloric acid or confuse precipitation colour with a flame colour. No visible result may reflect concentration or contamination limits and should be recorded honestly. A single anion test cannot identify the unknown’s cation. This separate Chemistry section applies on both tiers.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Hydrochloric acid is interchangeable with nitric acid in the silver-nitrate halide test. This claim is false: Do not say chloride gives a yellow precipitate, replace nitric acid with hydrochloric acid or confuse precipitation colour with a flame colour. No visible result may reflect concentration or contamination limits and should be recorded honestly. A single anion test cannot identify the unknown’s cation. This separate Chemistry section applies on both tiers.
Chemistry-only: acidified silver nitrate distinguishes three halides: Nitric acid does not introduce a halide ion that would contaminate this test. Using hydrochloric acid instead introduces chloride and can produce a misleading white precipitate with silver nitrate. Acidification also removes carbonate interference in the standard comparison. The school method governs quantities and handling. Silver-halide colours are subtle, so compare known results side by side under the same light rather than relying on a tiny colour difference from memory.
Hydrochloric acid is interchangeable with nitric acid in the silver-nitrate halide test.
Do not say chloride gives a yellow precipitate, replace nitric acid with hydrochloric acid or confuse precipitation colour with a flame colour. No visible result may reflect concentration or contamination limits and should be recorded honestly. A single anion test cannot identify the unknown’s cation. This separate Chemistry section applies on both tiers.
The stated dilute-nitric-acid and silver-nitrate precipitation test for halide ions: write the technical term.
halide test means The stated dilute-nitric-acid and silver-nitrate precipitation test for halide ions.