In everyday life a pure substance is one which has had nothing added to it like milk An impure substance would be one with other things added like chocolate milk In chemistry A pure substance consists of a ID: 1039249
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1. Chemical Analysis
2. Pure and impureIn everyday life a pure substance is one which has had nothing added to it, like milk.An impure substance would be one with other things added, like chocolate milk
3. In chemistry:A pure substance consists of a single element or a single compound and nothing elseImpure substances are mixtures and contain other substances
4. We can tell the difference by looking at melting and boiling points. Pure substances will have a very sharp melting and boiling point.For example, pure water freezes at exactly 0°CImpure substances will tend to melt or boil across a range of temperaturesFor example, impure water might begin freezing at 4°C and finish freezing at 0°C
5. Questions 1 and 2 on page 181
6. Formulations
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8. Formulations are carefully designed mixtures with many ingredients in very specific amounts. Each of the ingredients has a purpose.Examples include fuels, paints, medicines, alloys and many more
9. Chromatography
10. Paper - this is called the stationary phase Each constituent moves a different distance up the paperThe starting line for the spots must be drawn in pencil otherwise the line will also be carried up the paperThe solvent. We normally use water or ethanol. The solvent is called the mobile phase as it moves up the paper and carries the substances with itThe substances to be tested are placed on the line. Each one is a mixture made of constituentsThe top of the solvent must be below the pencil line or the substances to be tested will dissolve away from the paperThe solvent travels up the paper. Where it stops is called the solvent frontA beaker
11. AnalysisIn this case, spot 1 and 3 are made of two constituents so are impure.Spot 2 is made from one constituent so is pure.Spot 1 has two constituents, one of which also makes up spot 2.Spot 3 has two constituents, but neither of those are present in spot 1 or 2Q1-4
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13. Finish questions
14. Gas testsTest for:HydrogenOxygenCarbon DioxideChlorine
15. Use page 184-185 to complete the table then answer all questions.GasWhat you doWhat you observe if gas is presentHydrogenHold a lighted splint near the gasHear a squeaky popOxygenThe limewater turns milky (cloudy white)Chlorine
16. Further Analysis – Triple only
17. Further Analysis – Triple onlyFlame tests:lithium compounds result in a crimson flamesodium compounds result in a yellow flamepotassium compounds result in a lilac flamecalcium compounds result in an orange-red flamecopper compounds result in a green flame.
18. Instrumental AnalysisInstrumental analysis uses complicated scientific equipment to analyse substancesAdvantages: Accurate SensitiveRapid
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20. Flame emission spectroscopy
21. Tests for ions in solutionCation tests (positive ions – so metals)Anion tests (negative ions – non-metals)
22. Cation tests
23. Cation testsSodium hydroxide solution can be used to identify some metal ions (cations).Solutions of aluminium, calcium and magnesium ions form white precipitates when sodium hydroxide solution is added but only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.Solutions of copper(II), iron(II) and iron(III) ions form coloured precipitates when sodium hydroxide solution is added.Copper(II) forms a blue precipitate, iron(II) a green precipitate and iron(III) a brown precipitate.Balanced equations for each
24. Anion testsCarbonates react with dilute acids to form carbon dioxide gas. Carbon dioxide can be identified with limewater.Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow.Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
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27. Required prac 7Demos
28. Conduct a flame test on each of the solutionsNote the colour and therefore the metal involvedNaOH test:Put 2 cm3 of the test solution in a test tube, and add sodium hydroxide solution drop-wise until no further change.Note the colour of the precipitate and whether it dissolves in excess sodium hydroxide.Repeat for each test solution in turn and record your results in a tableChromatography questionsBalanced equation for each NaOH testQ04.1 04.5 on 193
29. 1a Explain why it would be difficult to distinguish between lithium chloride and calcium chloride using a flame test (2 marks) b Explain why this method cannot be used to identify the metal ions present in a solution containing a mixture of sodium chloride and potassium chloride. (2 marks)2 The precipitate formed when sodium hydroxide reacts with solutions containing metal ions is the corresponding METAL HYDROXIDE. a Write word equations and symbol equations (including state symbols) to show how the following solutions react with sodium hydroxide: i magnesium sulfate, MgSO4 ii iron(II) sulfate, FeSO4 iii iron(III) chloride, FeCl3 iv copper(II) chloride, CuCl2 (8 marks) b Write balanced ionic equations, including state symbols, for these four reactions .