AS-Level Chemistry

Unit 2: Application of Core Principles of Chemistry

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  • Created by: Jagjeet
  • Created on: 27-03-12 20:06

Group 1 and 2 compounds

Flame test:

1) Mix a sample amount of the compound with a few drops of hydrochloric acid this is because chlorides are very volatile.

2) Heat platinum or nichrome wire in a hot Bunsen burner flame to clean it this prevents the wrong colour being observed.

3) Dip the wire into the compound/acid micture and place in hot (roaring) flame to note the colour produced.

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Group 1 and 2 compounds

Explanation:

-energy abosed from flame causes electrons to move to higher energy levels

-electons fall back down to lower energy levels, releasing energy in form of light

-difference between the higher and lower levels determines the wavelength of light released which determines the colour of light.

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Group 1 and 2 compounds

Flame colours:

Li- Lithium RED

Rb- Rubidium RED

Ca- Calcium brick-RED

Sr- Strontium RED

Na- Sodium ORANGE/YELLOW

Ba- Barium GREEN

Cs- Caesium BLUE

K- Potassium LILAC

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Group 1 and 2 compounds

Thermal stability of Carbonates and Nitrates

Theraml decomposition is when a substance breaks down when heated.

-carbonates and nitrate ions are large and made unstable by presence of cation. Cation polarises anion distorting it. Greater distortion=less stable anion. Large cations cause less distortion than small cations so more stable the carbonate/nitrate anion down the group. Thermal stability increases.

-2MNO3(s)-> 2MNO2(s) +O2(g)

-MCO3(s)->MO(s) + CO2(g)

-2M(NO3)2(s)->2MO(s) + 4NO2(g) + O2(g)

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