Chemical Analysis
- Created by: FM 1
- Created on: 08-10-17 19:25
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- Chemical Analysis
- Flame Tests
- Are used to analyse metal compounds to identify which metal ions (cations) are present.
- Li+= Crimson flame. Na+=Yellow flame. Ca2+=Orange-red flame. K+=Lilac flame. Cu2+=Green flame
- When a metal ion is heated it absorbs energy. This excited electrons and causes them to move to higher energy levels.
- The excited electrons release their excess energy as visible light before moving back to their regular orbits.
- The difference in electron arrangement between metals leads to the release of different amounts of energy, thus different wavelengths of light.
- The excited electrons release their excess energy as visible light before moving back to their regular orbits.
- Flame tests can not identify the metals in mixtures of metal ions.
- Some flame colours are stronger than others, thus flame colours may be masked.
- There may be more of certain metals in the mixture.
- Flames test are only useful when testing a substance containing only a single metal ion (cation)
- One colour is produced because the light produced this is a combination of the wavelenghts in the spectrum
- Flame Emission Spectroscopy
- Spectroscopy is the process of investigating substances using electromagnetic radiation. Different techniques use different frequencies of electromagnetic radiation
- Flame emission spectroscopy uses visible light
- Spectroscopy allows chemists to identify elements in mixtures and investigated the detailed structure of compounds.
- An instrumental method used to analyse metal ions in solution.
- 1.The sample is passed through a flame.
- 2. When a metal ion is heated it emits light at specific frequencies and wavelengths, this light is passed through a spectroscope.
- 3.A line spectrum is then created. This can be analysed to identify the metal ions in the sample and measure their concentration.
- 2. When a metal ion is heated it emits light at specific frequencies and wavelengths, this light is passed through a spectroscope.
- A line spectrum shows the specific wavelength of a sample as a series of lines.
- Each metal ion has a unique line spectrum
- Concentration
- The emission intensity of the spectrum will increase of there are more metal ions present- giving a less faded line spectrum for that elements.
- The line spectrum for a concentratedsample may also show wavelengths of emitted light that are to weak to show up in samples with a lower concentration
- Spectroscopy is the process of investigating substances using electromagnetic radiation. Different techniques use different frequencies of electromagnetic radiation
- Chromatography
- Used to seperate a mixture into its different compoents
- Two phases are present in chromatography
- Stationary phase- a solid or liquid
- A mobile phase-a liquid or gas that flows over the stationary phase
- The mobile phase acts as a solvent, meaning that the substance to be tested dissolves in the mobile phase.
- The mobile phase contains the dissolved components of of a mixture- it flows up the stationary phase, carrying the different components.
- This allows the two phases to exchange components-the components in the mobile phase can attach tot he stationary phase.
- Precipitation reactions
- Identifying positive ions (+)
- Some transition metals form hydroxide precipitates that have coloured characteristics.
- Copper reacts with sodium hydroxide to form a blue precipitate.
- Iron (ll) reacts with sodium hydroxide to form a green precipitate
- Iron(lll) reacts with sodium hydroxide to form a brown precipitate
- Several metals form hydroxide precipitates that are white.
- Aluminium hydroxide.
- Calcium hydroxide.
- Magnesimun hydroxide.
- Zinc hydroxide.
- If an excess of sodium hydroxide is added only the aluminium and zinc precipitate will dissolve.
- In the presence of excess ammonia solution, zinc hydroxide precipitate dissolves. Aluminium hydroxide precipitate is insoluble in excess ammonia solution.
- Some transition metals form hydroxide precipitates that have coloured characteristics.
- Identifying negative ions (-)
- Testing for carbonate ions.
- Carbonates react with dilute acids to produce CO2 and H2O
- Limewater (dilute calcium hydroxide) turns cloudy if carbonate ions are present
- Carbonates react with dilute acids to produce CO2 and H2O
- Testing for halide ions
- Nitric acid is added to the test solution to make it acidic. Then silver nitrate solution is added and a precipitate will form if halide ions are present
- Iodide forms a yellow precipitate .
- Bromide forms a cream precipitate.
- Chloride forms a white precipitate.
- Nitric acid is added to the test solution to make it acidic. Then silver nitrate solution is added and a precipitate will form if halide ions are present
- Testing for sulfate ions.
- The test solution is acidified using a few drops of dilute hydrochloric acid, and then a few drops of barium chloride solution are added.
- A white precipitate of barium sulfate forms if sulfate ions are present.
- The test solution is acidified using a few drops of dilute hydrochloric acid, and then a few drops of barium chloride solution are added.
- Testing for carbonate ions.
- Identifying positive ions (+)
- Flame Tests
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