Chemistry-only: identify five metal ions by flame colour
| English | 中文 | Pinyin |
|---|---|---|
| flame test/fleɪm test/ | 焰色试验 | yàn sè shì yàn |
| cation/ˈkætaɪən/ | 阳离子 | yáng lí zi |
What would explain this observation?
- A yellow flame can dominate a mixed sample even when another ion is present. A clean wire and reference colours matter when interpreting a flame test 焰色试验.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Flame tests identify some positive metal ions, or cations 阳离子, in compounds. The required colours are lithium crimson, sodium yellow, potassium lilac, calcium orange-red and copper green. State the ion and observation together. These are flame colours, not necessarily the colour of the original solid or solution. The source does not require memorising other metal-ion flame colours.
- flame test: A qualitative test using the characteristic flame colour produced by a stated metal-ion sample; cation: An ion with a positive electrical charge.
Which required flame colour supports potassium ions?
A sample is introduced into a suitable flame using the school-approved wire or soaked-splint method. Compare its emission with known references under the same conditions. A mixture may have masked colours; intense sodium emission can obscure another response. Yellow therefore supports sodium in the tested conditions but does not prove no other ions are present. Contamination of the wire, sample or apparatus can produce a misleading result.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A sample is introduced into a suitable flame using the school-approved wire or soaked-splint method. Compare its emission with known references under the same conditions. A mixture may have masked colours; intense sodium emission can obscure another response. Yellow therefore supports sodium in the tested conditions but does not prove no other ions are present. Contamination of the wire, sample or apparatus can produce a misleading result.
- For actual RP7 school work, use labelled known compounds, approved small amounts and a blue Bunsen flame under supervision. Clean the nichrome wire by the approved method between samples; the acquired handbook suggests fine emery paper and explicitly excludes concentrated hydrochloric-acid watch glasses for GCSE students. Record actual observed colour before naming the cation. Prepared reference photographs or a teacher demonstration can support interpretation but do not silently certify individual practical performance.
Which two habits make the investigation or model in this case more defensible?
For actual RP7 school work, use labelled known compounds, approved small amounts and a blue Bunsen flame under supervision. Clean the nichrome wire by the approved method between samples; the acquired handbook suggests fine emery paper and explicitly excludes concentrated hydrochloric-acid watch glasses for GCSE students. Record actual observed colour before naming the cation. Prepared reference photographs or a teacher demonstration can support interpretation but do not silently certify individual practical performance.
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: an original record contains five unknown samples with flames crimson, yellow, lilac, orange-red and green. Using the required reference table identifies Li, Na, K, Ca and Cu respectively. If three of ten properly recorded samples are lilac, their sample proportion is 3/10×100=30%; it is not potassium concentration or the proportion of potassium atoms in one sample.
Four of ten supplied unknown samples give a lithium-crimson flame. Calculate their sample percentage. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Four of ten supplied unknown samples give a lithium-crimson flame. Calculate their sample percentage.
The result is 40 %. Known: an original record contains five unknown samples with flames crimson, yellow, lilac, orange-red and green. Using the required reference table identifies Li, Na, K, Ca and Cu respectively. If three of ten properly recorded samples are lilac, their sample proportion is 3/10×100=30%; it is not potassium concentration or the proportion of potassium atoms in one sample.
Check the conclusion and its limits
- Do not identify chloride ions from a sodium-yellow flame or infer a salt’s complete formula from its cation alone. A negative or masked result may be inconclusive. A flame colour is qualitative evidence; concentration measurement requires a calibrated instrument and appropriate data. Separate Chemistry flame-test content applies to both tiers.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A yellow flame proves that no other metal ions are present. This claim is false: Do not identify chloride ions from a sodium-yellow flame or infer a salt’s complete formula from its cation alone. A negative or masked result may be inconclusive. A flame colour is qualitative evidence; concentration measurement requires a calibrated instrument and appropriate data. Separate Chemistry flame-test content applies to both tiers.
Chemistry-only: identify five metal ions by flame colour: A sample is introduced into a suitable flame using the school-approved wire or soaked-splint method. Compare its emission with known references under the same conditions. A mixture may have masked colours; intense sodium emission can obscure another response. Yellow therefore supports sodium in the tested conditions but does not prove no other ions are present. Contamination of the wire, sample or apparatus can produce a misleading result.
A yellow flame proves that no other metal ions are present.
Do not identify chloride ions from a sodium-yellow flame or infer a salt’s complete formula from its cation alone. A negative or masked result may be inconclusive. A flame colour is qualitative evidence; concentration measurement requires a calibrated instrument and appropriate data. Separate Chemistry flame-test content applies to both tiers.
A qualitative test using the characteristic flame colour produced by a stated metal-ion sample: write the technical term.
flame test means A qualitative test using the characteristic flame colour produced by a stated metal-ion sample.