2025 Montfort Sec 6092 Revision Guide for Practical

6092 Practical Revision Guide Chemistry Practical Test Candidates may be asked to carry out exercises based on: 1. Titration, e.g. acid-base titration (with suitable indicators such as methyl orange, screened methyl orange, and thymolphthalein). Other types of titrations may also be required, and where appropriate, sufficient working details will be given. 2. Speeds of reaction that may involve measuring of quantities, e.g. temperature, volume, length, mass or time measurements 3. Experiments involving separation techniques such as paper chromatography, filtration and distillation 4. Salt preparation 5. Gas collection Candidates would not be required to carry out drying of gases during practical examination. 6. Qualitative inorganic analysis involving an element, a compound or a mixture, including displacement reactions and tests for oxidising and reducing agents. Candidates should be familiar with the reactions of cations, reactions of anions and tests for gases as detailed in the Notes for Qualitative Analysis. Candidates would not be required to carry out tests involving sulfur dioxide gas. Reactions involving ions not included in the Notes for Qualitative Analysis may be tested: in such cases, candidates will not be expected to identify the ions but only to draw conclusions of a general nature. Candidates should not attempt tests, other than those specified, on substances, except when it is appropriate to test for a gas. 7. Qualitative organic analysis requiring a knowledge of simple organic reactions as outlined in Topic 11 Organic Chemistry, e.g. test-tube reactions indicating the presence of unsaturation (C=C) may be set, but this would be for the testing of observation skills and drawing general conclusions only.

Practical Techniques a) Candidates should normally record burette readings to the nearest 0.05 cm3 and they should ensure that they have carried out a sufficient number of titrations, e.g. in an experiment with a good end-point, two titres within 0.20 cm3. b) In qualitative analysis, candidates should use approximately 1 cm depth of a solution (1– 2 cm3) for each test and add reagents slowly, ensuring good mixing, until no further change is seen. Candidates should indicate at what stage a change occurs. Answers should include details of colour changes and precipitates formed, and the name and test for any gases evolved.

Tips on Qualitative Analysis A. Procedures for Heating 1. Keep the air hole closed when lighting a Bunsen burner. 2. When the Bunsen burner is lighted, open the air hole a little. 3. Use a test tube holder when heating anything in a test tube. 4. Slant the test tube. 5. Point the mouth of the test tube away from yourself and anyone nearby. 6. While heating, remove the test tube from the flame every now and then and shake the tube gently. (to prevent the solution from splurting out) 7. Ensure that the test tube is dry if you are heating a solid and observe if any water droplets formed at the side of test tube during heating. B. Recording Observations 1. Record your observations (in pen) as you are conducting the tests. This will ensure that important observations are not left out. 2. Negative results must be recorded as correct inferences can be drawn from these. Example of negative results: No precipitate is formed or solution remains colourless. 3. If a precipitate forms slowly, say so in your record of observations. 4. There is an observation for every test. IF you do not observe any change, then you should record ‘no visible change’ or ‘no visible reaction’. Do not leave a blank space in your record. 5. Record your observations directly next to the instructions. This is important when the test instructions consist of two or more separate steps. 6. You must only carry out the tests in the practical examinations. You must NOT do extra tests of your own (unless asked to do so). 7. Remember that the practical exam tests your practical skills, observation powers and ability to make correct conclusions.

(a) Tests for Cations You are expected to test for and identify cations and use these test results to answer questions in the conclusion. Cations can be identified by using sodium hydroxide solution and aqueous ammonia. All cations (except Na+, K+ and NH4+) give precipitate with these alkalis. Objectives 1. To note the colour of the precipitate produced. 2. To see whether the precipitate is soluble or insoluble in an excess of the reagent. cation effect of aqueous sodium hydroxide effect of aqueous ammonia (ammonium hydroxide, NH4OH) type of reaction ammonium (NH4+) • on warming, gas produced turns damp red litmus paper blue • ammonia gas produced - alkali + ammonium salt → salt + ammonia gas + water calcium (Ca2+) • white ppt., insoluble in excess • calcium hydroxide formed no ppt. precipitation copper(II) (Cu2+) • light blue ppt., insoluble in excess • copper(II) hydroxide formed • light blue ppt., soluble in excess giving a dark blue solution • copper(II) hydroxide formed precipitation iron(II) (Fe2+) • green ppt., insoluble in excess • iron(II) hydroxide formed • green ppt., insoluble in excess • iron(II) hydroxide formed precipitation iron(III) (Fe3+) • red-brown ppt., insoluble in excess • iron(III) hydroxide formed • red-brown ppt., insoluble in excess • iron(III) hydroxide formed precipitation

zinc (Zn2+) • white ppt., soluble in excess giving a colourless solution • zinc hydroxide formed • white ppt., soluble in excess giving a colourless solution • zinc hydroxide formed precipitation aluminium • white ppt., soluble in excess giving a colourless solution • aluminum hydroxide formed • white ppt., insoluble in excess • aluminum hydroxide formed precipitation Procedures 1. Use about 2 cm3 (approximately 1 cm depth) of solution containing the cation. 2. Get ready the materials (damp red litmus paper) if ammonia is expected to be formed. 3. Add 2 to 3 drops of aqueous sodium hydroxide or aqueous ammonia slowly. 4. Mix the solutions by shaking it thoroughly after each addition of reagent. 5. Look out for the formation of any precipitate. Note the colour carefully. 6. When carrying out an experiment, always leave the tube to stand for one or two minutes as some changes take some time. 7. Add more (excess) aqueous sodium hydroxide or aqueous ammonia. 8. Observe if the precipitate formed dissolves in an excess of the reagent. You may need to shake the test tube slightly. Explanation Compounds that are insoluble in water appear in the form of a precipitate. When aqueous sodium hydroxide (contains OH– ions) is added to a cation, a hydroxide is formed. Most metal hydroxides are insoluble in water. Examples: Cu2+(aq) + 2OH–(aq) → Cu(OH)2(s) Fe3+(aq) + 3OH–(aq) → Fe(OH)3(s)

Writing Observations test no. test observations 1 (a) To a portion of solution X, add dilute sodium hydroxide until a change is seen. (b) Add an excess of dilute sodium hydroxide to the mixture from (a). A white precipitate is formed. The white precipitate is soluble in excess dilute sodium hydroxide, forming a colourless solution. 2 (a) To a portion of solution X, add dilute ammonia solution until a change is seen. (b) Add an excess of dilute ammonia to the mixture from (a). A white precipitate is formed. The white precipitate is insoluble in excess dilute sodium hydroxide.

(b) Tests for Anions You are expected to test for and identify anions and use these test results to answer questions in the conclusion. Some anions (Cl– or SO42–) can be identified by the precipitates which their solutions give with different reagents. Objectives 1. To note the c