TOPIC 5- separate chemistry 1
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Where are transition metals positioned in the periodic table?
Right in the middle (between group 2 and 3)
Properties of transition metals
Similar to that of typical metals Hard, strong, shiny, sonorous, malleable, heat/electricity conductors, high melting points, high densities. Good catalysts V colourful
Examples of transition metals used as catalysts
Iron is used in the Haber process to make ammonia. Vanadium pentoxide is used in the Contact process to make sulfuric acid.
Densities of transition metals
High densities In general, transition metals have higher densities than group 1 metals.
How are alloys stronger?
Pure metals regular arrangement enables the layers of ions to slide over each other. However alloys have different sized atoms so layers can’t slide over each other as easily.
Alloys of iron
Steels Made by adding carbon to pure iron. Or stainless steel is made by adding chromium and nickel.
Strength of steel
Harder than iron and stronger (as long as carbon percentage doesn’t exceed 1%. Is less corrosive
Bronze
Copper + tin Harder than copper, used to make medals, decorative ornaments and statues.
Brass
Copper + zinc More malleable, used when less friction is required Water taps and door fittings
Gold alloys
Harder than pure, soft, malleable gold. 1 carat (1/24)
Aluminium alloys
Aluminium has a low density but isn’t strong enough for aeroplanes. Allowed to increase strength
Magnalium
Aluminium + magnesium Stronger, lighter and corrodes less easily than pure aluminium. Makes parts for cars and aeroplanes. High magnesium content is used in fireworks as burns brightly.
Corrosion
Metals reacting with oxygen to form metal oxides in the presence of oxygen and water.
What type of reaction is corrosion? How ?
Redox reaction Metal loses electrons (oxidised) Oxygen gains electrons (reduced)
Rusting
Corrosion of iron Occurs when iron is in contact w oxygen and water.
Experiment to show both oxygen and water are needed for iron to rust
Put iron nail in boiling tube w just water (boiled before to remove oxygen and oil to stop oxygen getting in) > won’t rust Put iron nail in tube w just air (calcium chloride absorbs any water from air) > won’t rust Our iron nail in boiling tube of water and oxygen > will rust
2 methods to prevent rusting
Barrier Sacrificial
Barrier methods to prevent rusting
Painting Oiling/greasing (particularly w moving parts)
Sacrificial protection methods to prevent rusting
Galvanising (coat of zinc on iron object, more reactive) Electroplating
Electroplating How is it carried out?
Coating the surface of a metal with another metal using electrolysis. Cathode (object you what electroplated) Electrolyte (solution w ions of the metal you’re plating) Anode (metal you what to electroplate w)
What are titrations used for?
Allow you to find out exact amount of acid needed to neutralise given quantity of alkali.
How do you carry out a titration?
Use a pipette to measure out a set volume of alkali into a flask w a few drops of indicator (phenolphthalein/methyl orange). Fill a burette w standard solution of acid. Add acid to alkali little at a time and mix regularly, going slower when you think it’s close to neutralisation. (Can use rough titration first). Indicator changes colour when is neutralised, record volume needed. Repeat to receive similar results and take mean.
Why can’t you use a universal indicator in titrations?
Because you want a single colour change and universal indicator changes colour gradually.
Safety precautions in titrations
Keep burette below eye level while you fill it so no acid gets in your eyes.