# Ion Tests - Cation, Anion and Gas Tests, Flame Test Colours and Unknown Identification

> Free qualitative analysis reference: tests for common cations, anions and gases with equations, an unknown-solution simulator and a test planner.

- URL: https://qilingtools.com/en/chemistry/qualitative
- Category: Chemistry Tools (https://qilingtools.com/en/chemistry)
- Tags: [Chemistry](https://qilingtools.com/en/tags/chemistry)
- Last updated: 2026-10-29
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

An ion test is a reagent, a procedure, an observation and a conclusion — and the order of adding reagents often matters. To test for sulfate, first add excess dilute HCl; only if there is no precipitate or gas do you add BaCl₂, and a white precipitate then confirms SO₄²⁻. The acid removes interference from Ag⁺, CO₃²⁻ and SO₃²⁻, and nitric acid must not be used because it oxidises sulfite to sulfate. For iron(II), KSCN gives no colour until chlorine water is added and the solution turns blood red; for ammonium, warm with concentrated NaOH and test the gas with moist red litmus. This tool has test cards for 15 cations (H⁺, NH₄⁺, Na⁺, K⁺, Li⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, Fe³⁺, Fe²⁺, Al³⁺, Mg²⁺, Ag⁺, Zn²⁺), 11 anions (Cl⁻, Br⁻, I⁻, SO₄²⁻, CO₃²⁻, HCO₃⁻, SO₃²⁻, NO₃⁻, S²⁻, PO₄³⁻, OH⁻) and 9 gases (O₂, H₂, CO₂, NH₃, Cl₂, HCl, SO₂, NO₂, water vapour), each with the reagent, procedure, observation, ionic equation, interfering ions and practical notes, all searchable. The simulator draws a random unknown from 23 common solutions; you add reagents, read the observations and name it. The planner takes 2–6 solutions and searches the reaction table for the shortest sequence of tests: for NaCl, Na₂SO₄ and Na₂CO₃, dilute HCl releases gas only from Na₂CO₃, then BaCl₂ gives a white precipitate only with Na₂SO₄, leaving NaCl (confirmed by AgNO₃). A flame-test gallery shows lithium, sodium, potassium, calcium, strontium, barium and copper colours with characteristic lines such as Na 589 nm.

## How to use

1. Browse or search the ion and gas test cards — try Fe3+, limewater or white precipitate
2. In the simulator, add reagents to the unknown, read the observations and submit your answer
3. In the planner, choose the solutions to tell apart and the reagents allowed, then read and copy the step-by-step scheme

## Features

- 35 test cards: 15 cations, 11 anions and 9 gases
- Reagent, procedure, observation, ionic equation, interferences and order of addition for every test
- Search by ion symbol, reagent or observation
- Unknown-identification simulator built on a 23-solution × 13-reagent reaction table
- Automatic planner for the shortest reagent sequence, with elimination and confirmatory tests
- Unreliable effects such as faint cloudiness from sparingly soluble salts are never used to distinguish
- Flame-test colour gallery with Na 589 nm, Li 670.8 nm and K lines
- Copy any card or plan as text

## FAQ

### Why add hydrochloric acid before barium chloride when testing for sulfate?

Excess dilute HCl removes ions that would also give a white precipitate with Ba²⁺ or Cl⁻: carbonate and sulfite are destroyed (as CO₂ and SO₂) and Ag⁺ is removed as AgCl. If the acidified solution then gives a white precipitate with BaCl₂, it contains sulfate. Do not acidify with nitric acid or use barium nitrate with HCl, because H⁺ with NO₃⁻ oxidises sulfite to sulfate and gives a false positive.

### How do you test for Fe²⁺ and Fe³⁺ ions?

Fe³⁺ turns KSCN solution blood red and gives a red-brown precipitate with NaOH. Fe²⁺ gives a white precipitate with NaOH that quickly turns grey-green and then red-brown; with KSCN it shows no colour until chlorine water or H₂O₂ is added, after which it turns red (add KSCN first). Potassium ferricyanide gives a blue precipitate with Fe²⁺ and is the method of choice when Fe³⁺ is also present.

### What colours do metal ions give in a flame test?

Lithium crimson, sodium intense yellow (589 nm), potassium lilac (viewed through cobalt-blue glass to block sodium yellow), rubidium red-violet, calcium brick red, strontium crimson red, barium pale yellow-green and copper green to blue-green. The flame test detects the element, not a particular ion, and the wire must be cleaned with dilute HCl and heated until it no longer colours the flame.

### How can I distinguish several colourless solutions with as few tests as possible?

Choose a reagent that gives as many different observations as possible, then test only the groups that still look the same. For example NH₄Cl, (NH₄)₂SO₄, Na₂SO₄ and NaCl can be told apart in one step with warm Ba(OH)₂ solution: precipitate plus ammonia means (NH₄)₂SO₄, ammonia only NH₄Cl, precipitate only Na₂SO₄, and no change NaCl. The planner in this tool searches for such shortest schemes automatically.

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