Chem 2
- Created by: A.B.
- Created on: 15-04-13 18:54
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- Chemistry Unit 3 Part 2
- Analysis and Synthesis
- Tests for positive ions
- Most Group 1 and Group 2 metals can be identified in their compounds using flame tests.
- Lithium (Li+) = Crimson
- Sodium (Na+) = Yellow
- Potassium (K+) = Lilac
- Calcium (Ca2+) = Red
- Barium (Ba2+) = Green
- Sodium hydroxide solution can be used to identify different metal ions, depending on the precipitate that is formed.
- Aluminium, calcium and magnesium ions all form white precipitates if added to sodium hydroxide.
- If more sodium hydroxide is added, the aluminium ions will dissolve. Then the magnesium ions and calcium ions can be distinguished using a flame test.
- Aluminium, calcium and magnesium ions all form white precipitates if added to sodium hydroxide.
- If sodium hydroxide is added to copper 2+, iron 2+ or iron 3+, a coloured precipitate is formed.
- Copper (2+) = light blue (precipitate).
- Iron 2+ = light green -> brown (precipitate)
- Iron 3+ = reddish brown
- Most Group 1 and Group 2 metals can be identified in their compounds using flame tests.
- Tests for negative ions
- We identify carbonates by adding dilute acid, which produces carbon dioxide gas. The gas turns limewater cloudy.
- We identify halides by adding nitric acid, then silver nitrate solution. This produces a precipitate of silver halide.
- Chloride = white precipitate
- Bromide = cream precipitate
- Iodide = pale yellow precipitate
- We add the nitric acid to remove any carbonate ions.
- We identify sulfates by adding hydrochloric acid, then barium chloride solution. This produces a white precipitate of barium sulfate.
- Titrations
- Titration is used to measure accurately how much acid and alkali react together completely.
- They form a salt + water
- The point at which an acid-alkali reaction is complete is called the end of the reaction.
- We us an indicator to show the end point of the reaction between an acid and an alkali.
- Titration is used to measure accurately how much acid and alkali react together completely.
- Chemical analysis
- Scientists working in environmental monitoring medicine and forensic science all need to analyse substances.
- Drugs, paints, remnants of an explosion, fire debris, gunshot debris, fibres, soil samples, toxic chemicals, biological toxins.
- The results of their analysis are often matched against existing databases to identify substances (or suspects in the case of forensics).
- Scientists working in environmental monitoring medicine and forensic science all need to analyse substances.
- Tests for positive ions
- Analysis and Synthesis
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