Theory
Qualitative analysis is the identification of the ions present in a sample by their characteristic reactions. This lab focuses on a specific set: the cations calcium, barium, potassium, and ammonium; the common anions; and the Group IA alkali-metal cations identified by flame colour. The skill is not just running a test, but choosing tests that distinguish ions which behave similarly.
1. The cations Ca²⁺, Ba²⁺, K⁺, and NH₄⁺
Calcium and barium are both Group 2 metals and behave alike: both give white precipitates with sulfate and with carbonate. To tell them apart you use the flame test (calcium gives a brick-red flame, barium a pale green) and the chromate test (barium gives a yellow precipitate of barium chromate; calcium does not). Potassium gives a lilac flame and no precipitate with common reagents. Ammonium is confirmed by warming with sodium hydroxide, which releases ammonia gas that turns damp red litmus blue.
2. Confirmatory tests for anions
The sulfate ion gives a white precipitate of barium sulfate with barium chloride, insoluble in dilute acid. The carbonate ion fizzes with dilute acid, releasing carbon dioxide that turns limewater milky. The chloride ion gives a white precipitate of silver chloride with silver nitrate, soluble in ammonia. The nitrate ion gives a positive brown ring test with iron(II) sulfate and concentrated sulfuric acid.
3. Group IA (alkali metal) analysis
The Group IA cations, lithium, sodium, and potassium, have very few precipitation reactions, so they are identified mainly by flame colour: lithium gives crimson, sodium an intense yellow, and potassium a lilac (pale violet) flame. Sodium's strong yellow can mask potassium; viewing the flame through blue cobalt glass filters out the sodium colour so the potassium lilac can be seen.
4. The logic of a separation scheme
Because several ions can be present at once, qualitative analysis uses a systematic scheme: tests are run in an order that removes or confirms one ion before the next, so that a positive result is not confused by another ion. The confirmatory test for each ion is the one that is unique to it.
Apparatus and Reagents
The equipment and reagents a real qualitative-analysis experiment uses. In this simulation they are modelled for you, but the observations correspond to what each test would actually show.
- Test tubes, test-tube rack, dropper pipettes, and a Bunsen burner with a clean nichrome wire for flame tests.
- A piece of blue cobalt glass for viewing potassium flames.
- Red and blue litmus paper; limewater for carbon dioxide.
- Reagents: dilute and concentrated hydrochloric and sulfuric acids, sodium hydroxide, barium chloride, silver nitrate, potassium chromate, iron(II) sulfate.
- Salt samples of the cations (calcium, barium, potassium, ammonium, lithium, sodium) and of the anions (sulfate, carbonate, chloride, nitrate).
Instructions
This is a predict-and-check lab. In each tab you decide the answer yourself first, choose it, and only then does the simulation confirm the correct result so you can compare. Record every result in your worksheet.
Simulation — The Qualitative Analysis Bench
Team Questions
Work these out with your team, type each answer, and check it.
Example Lab Report
A worked example showing the expected format and the predict-and-check workflow.
Qualitative Analysis: Ca, Ba, K, Ammonium, Anions, and Group IA
Chemistry | Section: [Your Section] | Date: [Date]
Lab Members: [Names of all members present]
Objective — To identify the cations calcium, barium, potassium, and ammonium, the common anions, and the Group IA alkali-metal cations, using characteristic and confirmatory tests, and comparing every prediction with the simulation.
Part A — Cations (worked example)
Calcium and barium both gave white precipitates with sulfate, so they were distinguished by other tests: calcium gave a brick-red flame and no chromate precipitate, while barium gave a pale green flame and a yellow precipitate with potassium chromate. Potassium gave a lilac flame. Ammonium released ammonia on warming with NaOH, turning red litmus blue.
Part B — Anions (worked example)
Sulfate gave a white precipitate with barium chloride, insoluble in acid. Carbonate fizzed with acid, turning limewater milky. Chloride gave a white silver precipitate soluble in ammonia. Nitrate gave a positive brown ring test.
Part C — Group IA (worked example)
Lithium gave a crimson flame, sodium an intense yellow, and potassium a lilac flame. In a sodium-plus-potassium mixture, the sodium yellow masked the potassium until the flame was viewed through blue cobalt glass. Group IA ions gave essentially no precipitation reactions.
Part D — Identify the Unknown (worked example)
Each unknown was identified from its combination of results, for example a brick-red flame with a white sulfate precipitate and no chromate precipitate was calcium. All identifications matched the simulation.
Discussion and Conclusion — Every prediction agreed with the simulation. Ions that behave similarly, especially calcium and barium, were distinguished by combining the flame test and the chromate test, and the Group IA cations were identified by flame colour with cobalt glass used to reveal potassium.
Practice Quiz
For extra practice on this topic, use the interactive Qualitative Analysis quiz in the Quizzes section of the site.