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Revision notes - Test For Gases and Ions

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Introduction

Tests for Gases Name Formula Test Observations Hydrogen H2 Ignite gas. Squeaky pop is heard. Oxygen O2 Place a glowing splint in a sample of the gas. The glowing splint relights. Carbon dioxide CO2 Bubble gas through limewater (saturated solution of calcium hydroxide) A solution turns from colourless to cloudy. A white (milky) precipitate of calcium carbonate forms which is sparingly soluble. Ammonia NH3 Test for gas using damp red litmus paper. Litmus paper turns blue. Chlorine Cl2 Test 1 Test for gas using damp litmus paper (red or blue) Chlorine bleaches the litmus paper very quickly. Test 2 Test for gas using moist starch-iodide paper. The paper turns blue-black. Test 3 Pass gas through a solution of a bromide. The solution turns from colourless to orange. Test 4 Pass gas through a solution of an iodide. The solution turns from colourless to brown (possibly with a black precipitate, iodine). ...read more.

Middle

Sulphate (VI) SO42- Test Add barium chloride solution acidified with dilute HCl to the test solution. White precipitate of barium sulphate forms. Sulphite SO32- Test Warm the sulphite with dilute HCl. Test for gases using acidified potassium dichromate(VI) solution (or paper) The solution turns green. Chloride Cl- Test 1 Add concentrated sulphuric acid to the solid chloride. White steamy acidic fumes are seen - HCl fumes. Test 2 Add dilute nitric acid to a solution of a chloride to acidify the solution. This eliminates any carbonates or sulphites. Add silver chloride to the solution. Add dilute ammonia solution. White precipitate of AgCl forms. Solid dissolves. Bromide Br- Test 1 Add concentrated sulphuric acid to the solid bromide. Steamy brownish acidic fumes are seen. Test 2' Add dilute nitric acid to a solution of a bromide to acidify the solution. This eliminates any carbonates or sulphites. Add silver nitrate to the solution. ...read more.

Conclusion

Lithium Li+ Test Dip nichrome wire in HCl. Dip wire in solid. Heat wire in centre of flame. Observe colour of flame. A carmine red flame is seen. Sodium Na+ Test Dip nichrome wire in HCl. Dip wire in solid. Heat wire in centre of flame. Observe colour of flame. A yellow flame is seen. Potassium K+ Test Dip nichrome wire in HCl. Dip wire in solid. Heat wire in centre of flame. Observe colour of flame. A lilac flame is seen. Magnesium Mg2+ Test Add NaOH solution to the magnesium solid. A white solid forms which is insoluble in excess NaOH(aq). This is Mg(OH)2(s) Calcium Ca2+ Test Dip nichrome wire in HCl. Dip wire in solid. Heat wire in centre of flame. Observe colour of flame. A brick red flame is seen. Strontium Sr2+ Test Dip nichrome wire in HCl. Dip wire in solid. Heat wire in centre of flame. Observe colour of flame. A crimson red flame is seen. Barium Ba2+ Test Dip nichrome wire in HCl. Dip wire in solid. Heat wire in centre of flame. Observe colour of flame. A apple green flame is seen. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This is an excellent summary of the different tests for gases and ions. This work deserves 4/5 but with a few minor changes could easily reach 5/5.
- structure is a little odd in places, resulting in repetition. Differentiation within the ion section would help with this.
- there should be greater use of chemical equations, as generally this helps with explanations.

Additionally, some explanation as to why various tests give certain results would be beneficial. Many exam papers ask you to explain the tests and observations, as well as simply asking you to state them.

Marked by teacher Kathryn Bradley 24/09/2012

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