Paper 4 Flashcards
Group 1 alkali metals
Soft, relatively low melting points
Relatively low densities - first 3 can float on water
All have similar chemical properties - as 1 electron in outer shell. +water= metal hydroxide+H2. Metal hydroxide= Base that dissolves in water to form alkaline solution
Li- fizzes steadily, slowly becomes smaller until all reacted
Na- melts to form ball, fizzes rapidly, quickly becomes smaller until disappears
K- quickly melts to form a ball, burns violently w sparks and lilac flame, reacts rapidly with small explosion
Rb- melt very quickly, burn very violently, disappears almost instantly with an explosion
Group 7 halogens
Exist as simple molecules. Each molecule contains two halogen atoms joined by single covalent bond. Cl- pale green gas, Br- brown liquid, I- purple black solid
All have similar chemical properties - as all have 7 electrons in outer shell. +metals=salts. F- cold iron wool burns to produce white iron III fluoride, Cl- hot iron wool burns vigorously- orange-brown, Br- hot iron wool burns quickly- red-brown, I-hot iron wool reacts slowly in iodine vapour to produce grey iron iodide. hydrogen+=hydrogen halides (gas at room temp, dissolve in water to produce acidic solutions): F- explodes in cold and dark, Cl- explodes in flame/sunlight, Br-vigorous;
~needs burning hydrogen, I- very slow when heated strongly, forms some hydrogen iodide. At- react very slowly even when heated, little forms
Group 0 noble gases
Group 0- noble gases
Exist as single atoms
Low boiling points and densities
Inert
Reactivity of metals
- more- vigorous- easily loses electrons to form cations
- metal+water~>metal hydroxide+hydrogen
- Al=reactive but surface naturally forms thin layer aluminium oxide that keeps water away from metal below)
- Mg slowly reacts first added to water but layer of insoluble MgOH forms, protects metal/stops it from reacting
- but if steam passes over hot Mg, vigorous reaction happens to form MgO+H2
- metal+dilute acid-> salt+hydrogen -metal below hydrogen in RS will not react with dilute acids
Spectator ions
Ions that don’t take part in the reaction
Test for gases
- oxygen: glowing splint relight, as supports combustion
- hydrogen: lighted splint ignited with squeaky pop as H ignites in air
- carbon dioxide: when bubbled through limewater (CaOH solution), it turns cloudy white as CO2 reacts with CaOH solution to form white precipitate
- chlorine: red damp litmus paper bleached as it’s acidic gas that acts as a bleach. If blue litmus, turns red then bleach.
Flame test - metal ions
- Li+ Lithium Red
- Ca2+ Calcium Orange-Red
- Na+ Sodium Yellow
- Cu2+ Copper Green-Blue
- K+ Potassium Lilac
- clean w/ HCl/Nitric acid, rinse w/ deionised water. Dip clean nichrome wire loop into a sample of compound being tested. Put loop to edge of blue flame from Bunsen burner. Observe n record flame colour
Testing for Aqueous Metals Ions
- Dilute NaOH solution + metal ions -> metal hydroxide (but insoluble precipitate)
- Ca2+ and Zn2+ = white
- Fe2+ = green, Fe3+ orange-brown
- Cu2+ = blue
- add excess NaOH to differentiate Zn2+/Ca2+ = CaOH remains unchanged, ZnOH dissolves to colourless solution
Anions (testing for carbonate ions)
- Co3 2+
- add dilute HCl = bubbles given off, caused by carbon dioxide, bubbled through limewater to confirm its carbon dioxide
Anions (testing for sulfate ions)
- barium ions (Ba 2+) + sulfate ions (SO4 2-) -> insoluble white barium sulfate
- add dilute HCl to sample. Add dilute barium chloride solution. White precipitate
- acidified w/HCl to remove any carbonate ions present as it also w barium chloride to produce white precipitate
Halide ions testing
- Add dilute nitric acid to sample. Add dilute silver nitrate solution. Silver ions react with halide ions
- CBI, white cream yellow precipitate
- carbonate ions = white w silver nitrate solution so nitric acid reacts w it to remove them
Identifying ions in unknown salts
- dissolve sample of salt in a little of distilled water if solid salt and not salt solution
- very dilute solutions( of CBI in silver nitrate) makes it difficult to tell whether precipitate is a colour that is too pale
- harmful/toxic if inhaled/swallowed so only dilute solution used
Instrumental methods of analysis
Relies on machines
- extremely fast, quick speed
-sensitive, can detect the substance even in the smallest amounts of sample
-accurate, reliably identify elements and compounds
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Very expensive, laboratory glassware is cheaper and more readily available
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Examples: flame photometer, emission spectroscopy, gas chromatography
Flame photometer
Identify metal ions
Coloured light from vaporised sample is split to produce emission spectrum
Each metal ion produces unique emission spectrum, compare spectrum to known metal ion reference spectra and if match then same
