F332 - Elements from the sea

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Chemistry F332 Notes
Ions in solids and solutions:
Structure of an ionic lattice (Sodium Chloride):
Consists of sodium ions (Na+) surrounded by six chloride ions (Cl-)
Chloride ions also surrounded by six sodium ions.
Held together by attraction of oppositely charged ions.
Giant ionic lattice.
Electrostatic bonds hold lattices together.
Structure is simple cubic.
Some ionic crystals contain water.
Known as water of crystallisation.
These crystals are hydrated.
Blue copper sulphate crystals are the pentahydrate crystals ­ CuSO4.5H2O
If there is no water of crystallisation then the ionic crystal is said to be anhydrous.
Ionic substances in solution:
Many dissolve in water without difficulty.
Ions become surrounded by polar water molecules.
They spread out through the solution.
Hydrated ions are randomly arranged and behave independently.
Positive hydrogen atoms in water are attracted to negative ions.
Conversely the negative oxygen atoms are attracted to positive ions.
This is known as hydration.
Draw water molecules as wedges and ion as a circle.
Label the charged ends.
Ionic equations:
All nitrates are soluble in water.
All chlorides are soluble in water bar AgCl and PbCl2.
All sulfates are soluble in water bar BaSO4, PbSO4 and SrSO4.
All sodium, potassium and ammonium salts are soluble in water.
All carbonates are insoluble in water bar (NH4)2CO3 and those of group 1.
The ionic equation for a neutralisation reaction is always ­ H+(aq) + OH-(aq) H2O(l)
When writing an ionic equation label the charges on each ion then remove the spectator ions
(like ions in charge and state and on both sides of equation).
If there is a precipitation reaction one product will be a solid.
With neutralisation reacts a covalent compound is formed.
Atoms and ions:
First ionisation enthalpy:
Energy needed to remove one electron from each of one mole of isolated gaseous atoms of
an element.

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One mole of gaseous ions with one positive charge is formed: X(g) X+(g) + e-
The value of this is always positive.
Energy must be put in to remove electron which is attracted to the nucleus.
Largest enthalpies are noble gases, they have a full outer shell and all very unreactive.
Lowest enthalpies for group 1 elements, very reactive elements and only have 1 electron in
there outer shell.…read more

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Soluble in organic solvents.
Most reactive out of the halogens.
Displaces chlorine, bromine and iodine.
Benefits: used to make PTFE, in toothpastes to strengthen enamel, used to make HCFC's.
Risks: highly reactive and so handling must be kept to a minimum.
When needed for reactions it is made in situ by electrolysing HF.
Chlorine:
Green gas at room temperature.
Slightly soluble in water to give a pale green solution.
Soluble in organic solvents to give a green solution.
More reactive than bromine or iodine.…read more

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Reactions of halogens with halides:
1. Chlorine water, potassium bromide and cyclohexane ­
2.…read more

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Bromine water, potassium iodide and cyclohexane ­
The 3 above reactions take place as a halogen higher up in group 7 can displace one lower down.
Reactions of halide ions with silver ions:
1. Potassium chloride with silver nitrate ­
2. Potassium bromide and silver nitrate ­
3.…read more

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Electrolysis:
· An example of electrolysis:
· If we place aqueous sodium chloride into the electrolysis cell and allow current to
flow, the following reactions occur at the electrodes:
· At the cathode: Reduction
-
· 2H+(aq) + 2e H2(aq)
· At the anode: Oxidation
-
· 2Cl2 Cl2(g) + 2e
· Chlorine bleaches damp litmus paper.
· This leaves Na+(aq) and OH-(aq) in solution i.e. sodium hydroxide forming around the
cathode (turns litmus blue)
· Electrolysis of brine forms basis for CLORALKALI industry.…read more

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Polar molecules:
· A dipole occurs when a molecule has a positive and negative end.
· When a molecule has a dipole we say that it is polarised.
· Polar molecules have a permanent dipole.
Temporary or Instantaneous dipoles:
· The electron density is unevenly distributed.
· Instantaneous dipole.
· Swirling electron density distributions changes and therefore so does the polarity.
· If other molecules with a dipole are close they can induce a dipole.…read more

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Physical Properties:
· Boiling points increases with heavier halogen.
· Same with increasing number of halogen atoms.
· This is due to overall number of electrons increasing.
· Increases Id-Id bonds.
· Stronger intermolecular bonds = more energy needed to pull molecules apart.
Bond enthalpies:
· The C-Hal bond gets weaker as you go down the group.
· This makes bond easier to break and the compounds become more reactive.
· Bond strength has greatest effect on reactivity.
· As bond strength decreases, reactivity increases.…read more

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Five stages;
· Upper layer containing Chloroalkane is run off into clean beaker.
· Chloroalkane is shaken with sodium hydrogencarbonate to remove acidic impurities.
· Chloroalkane layer is run off again.
· Anhydrous sodium sulfate is added to remove any water (a drying agent).
· Chloroalkane is then purified via distillation.
Greener industry:
Batch and continuous process:
· Bath process; reactants placed in reaction vessel and are allowed to react. Once reaction is
over, products are removed and vessel is cleaned.…read more

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Also energy, so any heat which could be made during an exothermic reaction is converted
using a heat exchanger into hot water or steam.
Plant location:
· Good transport network; sea terminal and good rail and road links are in important to
bring in raw materials and distribution of product.
· Labour; often build near existing plants as there will be an availability of skilled labour.
· Shared facilities; product from one plant may be a feedstock for another.…read more

Comments

Emma Anderson8

I was Just wondering if the chemistry notes are for ocr salters chemistry B? :)

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