Chemistry revision!

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Chemistry revision!

1. The early periodic table
2. The modern periodic table
3. Group 1 alkali metals
4. Group 7 halogens
5. Transition elements
6. Strong and weak acids and alkalis
7. Titrations
8. Titration calculations
9. How ideas about acids and alkalis developed
10. Water and solubility
11. Solubility curves
12. Hard water

• Removing hardness
• Water treatment
• Comparing the energy produced by fuels
• Energy changes in reactions
• Calculations using bond energies
• Test for positive ions
• Tests for negative ions
• Testing for organic substances
• Instrumental analysis 1
• Instrumental analysis 2

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In the 19th Century some chemist dudes had a
fight

• In the 1800s people were on a roll discovering
  elements. Scientists didnt like how disorganised
  they were so they tried to organise them. The
  problem was they didnt know a whole lot about
  them!
• Not much was known about atoms
• Each element had several names
• A load of elements hadnt been discovered yet!

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John Dalton

• Dalton put the elements in order of mass,
  measured by doing different chemical reactions.
• Problem was, that didnt tell anyone a lot about
  the elements and when more elements were
  discovered the list had to be changed!

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John Newlands

• Newlands introduced a bit more order the law of
  octaves (8)
• He based this on the fact that every eighth
  element seemed to have similar properties.
• Problem is, he got a bit full of himself and
  tried to make all the elements fit in the octaves
  even if they didnt fit the pattern, assuming all
  had been discovered in spite of the fact new ones
  were being discovered all the time. He even put 2
  elements in one spot to make them all fit.
• All the other scientists laughed at him ?.

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Alexandre-Emile Beguyer de Chancourtois

• This French dude copied Newlands idea of octaves,
  but put them in a much clearer diagram.
• Unfortunately when his work was published the
  diagram was missed out!
• Without the diagram everyone got confused so they
  ignored him ?

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Dmitri Mendeleev

• This Russian dude cracked it.
• By the time he ordered the elements 50 had been
  discovered. He put them in order of atomic masses
  and then arranged them so a periodic pattern in
  their physical and chemical properties could be
  seen.
• The clever part was he left GAPS for elements
  that had not been discovered yet when the pattern
  wasnt followed. He could predict the properties
  of these elements thanks to his table.
• A few years later elements were discovered that
  fit Mendeleevs predictions.
• All the other scientists thought he was brilliant
  ?

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1. The Early Periodic Table

• Dalton elements in order of mass
• Newlands law of octaves, organised into similar
  properties
• Mendeleev periodic table used today. In order
  of atomic masses, and structured according to
  chemical and physical properties. He left gaps
  which were filled when new elements were
  discovered

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2. The modern Periodic Table

• Elements are arranged in order of their atomic
  (proton) number, and in groups of similar
  properties.
• Groups have the same number of electrons in their
  outer shell.

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3. Alkali Metals

• VERY reactive, stored in oil (fizz and burn H2
  with water)
• Reactivity increases down the group
• Low density (1st 3 float on water!)
• Soft (can cut with a knife)
• Low melting and boiling points for metals
• Melting points decrease down the group
• React with non-metals, losing their outer
  electron
• Lithium water ? lithium hydroxide hydrogen
• 2Li (s) 2H2O (l) ? 2LiOH (aq) H2 (g)
• Sodium chlorine ? sodium chloride
• 2Na (s) Cl2 (g) ? 2NaCl (s)

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4. Halogens

• Poisonous non-metals
• Coloured vapours
• Low melting and boiling points
• Poor conductors of heat and electricity
• Fluorine yellow gas
• Chlorine green gas
• Bromine orange/brown liquid
• Iodine gray solid violet vapour
• Go around in pairs (F2, Cl2)
• Less reactive as you go down the group
• H2(g) F2(g) ? 2HF(g)
• Displacement Cl2 2KBr ? 2KCl Br2

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5. Transition Elements

• Held together by metallic bonding
• Good conductors of heat and electricity because
  of delocalised electrons
• Hard, tough and strong
• Malleable
• High melting points (apart from mercury)
• Much less reactive than alkali metals (corrode
  slowly)
• Combining them makes useful alloys
• Make coloured compounds

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Task

• Page 222-3
• Summary questions 1 - 6

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Strong and weak acids/alkalis

• Acids form H ions when we add them to water
• HCl(g) ? H(aq) Cl-(aq)
• The H (hydrogen ion) is the acidic part.
• Acids are PROTON DONORS. A proton is an H
• Form OH- ions when we add them to water
• NaOH(s) ? Na(aq) OH-(aq)
• OH- (hydroxide ion) is the alkaline part.
• Alkalis are PROTON ACCEPTORS.
• An acid or base is STRONG if it completely
  ionises in water.
• An acid or base is WEAK if it only partially
  ionises in water.

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7. Titrations

• Indicators are used to show the endpoints of
  neutralisation reactions
• Strong acid strong alkali - Universal indicator
  or any other
• Weak acid strong alkali - Phenolphthalein
• Strong acid weak alkali - Methyl orange
• In a titration we need to use the correct
  indicator
• We also use pipettes to measure out fixed volume
  of solution and burettes to measure the volume of
  solution added.

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8. Titration Calculations

• On the bottles you find the name of the acid and
  alkali and a number followed by a M.
• M means the number of moles in 1000cm3 (or 1dm3)
  of solution. Molarity or molar concentration
  mean the same thing.
• n M x V (dm3) for liquids

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9. How ideas about acids and alkalis developed

• Liebig defined an acid as a compound that
  contained hydrogen which could react with a
  metal to produce hydrogen gas.
• Arrhenius defined an acid as a substance that
  produces hydrogen ions (H) in water, and bases
  as a substance that produces hydroxide ions (OH-)
  when dissolved in water.
• As Arrhenius definition only worked in aqueous
  solution another definition had to be developed.
• Brønsted and Lowry defined an acid as a proton
  donor and a base as a proton acceptor

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Task

• Page 232-3
• Summary Questions 1 3
• Exam style questions 1 - 2

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10. Water and solubility

• Soluble - substances that can dissolve.
• Insoluble substances that cannot dissolve.
• Solution - the mixture formed when a substance
  dissolves.
• Solute - the substance that dissolves.
• Solvent - the liquid in the solution.
• A saturated solution is one
• in which no more solute will
• dissolve at that temperature.
• When a hot saturated solution
• cools some of the solute will
• separate from the solution.

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11. Solubility Curves

• The solubility of most solid solutes increases as
  the temperature increases
• The solubility of gases decreases as temperature
  rises.
• The solubility of gases increases as pressure
  increases

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12. Hard water

• Soft water readily forms lather with soap. Hard
  water reacts with soap to form scum and so more
  soap is needed to form a lather.
• Hard water contains dissolved compounds, usually
  of calcium or magnesium. The compounds are
  dissolved when water comes into contact with
  rocks.
• Using hard water can increase costs because more
  soap is needed.
• Salts in the water react with the soap to produce
  stearates (scum)
• When hard water is heated it can produce scale
  (calcium carbonate) that reduces the efficiency
  of heating systems and kettles.
• Hard water has some health benefits because
  calcium compounds are good for health.
• Calcium is good for strong teeth and bones.
• There is evidence that drinking hard water
  reduces the chances of heart disease.

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13. Removing hardness

• Hardness is from dissolved calcium and magnesium
  ions. The ions come from rocks which the water
  has filtered through.
• The ions can be removed using washing soda
  (sodium carbonate), which precipitates the ions.
• An ion exchange column can be used. They contain
  sodium ions which can be exchanged with the
  calcium or magnesium ions.

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14. Water Treatment

• Water from boreholes is usually pretty clean,
  its been filtered by the surrounding rocks.
  Usually you just use chlorine to kill of germs.
• Water from rivers or reservoirs needs more
  treatment. Treatment involves chemical processes,
  like adding aluminium sulphate and lime, and
  physical processes, like filtration.
• Water that has been treated is not pure. It still
  contains substances dissolved in it.
• Pure water is produced by distilling it, boiling
  and condensing the steam produced, or deionising
  it by using an ion exchange column.

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Task

• Page 246-7
• Summary questions 1 - 3

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15. Comparing the energy produced by fuels

• The relative amounts of energy released when
  substances burn can be measured by simple
  calorimetry, e.g. by heating water in a glass or
  metal container. This method can be used to
  compare the amount of energy produced by fuels
  and foods.
• Energy is normally measured in joules (J). Some
  dietary information is given in calories, which
  are equal to 4.2 joules.
• Different foods produce
• different amounts of energy.
• Foods with higher proportions
• of carbohydrates, fats and oils
• produce relatively large amounts
• of energy.

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16. Energy changes in reactions

• Energy (heat) is being put in to break bonds in
  the reactants.
• At the top of the curve, the bonds in the
  reactants have been broken.The amount of energy
  put in to break these bonds is called the
  activation energy.
• The activation energy is the minimum amount of
  energy needed for the reaction to occur. A
  catalyst may work by lowering the activation
  energy for a reaction.
• Energy (heat) is given out as bonds form in the
  products.
• The difference in energy levels
• between the reactants and the
• products is given the symbol DH
• (pronounced 'delta H').This is the amount of
  heat given out
• (or taken in) during the reaction.For an
  exothermic reaction,
• DH is negative.For an endothermic reaction,
• DH is positive.

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17. Calculations using bond energies

• H2 Br2 ? 2HBr
• H H Br Br H Br H - Br
• H-H 436 kJ/mol, Br-Br 193jK/mol, H-Br
  366kJ/mol
• Reactants 436 193 629 kJ/mol
• Product 366 x 2 732 kJ/mol
• 629 732 -103 kJ/mol -ve means exothermic

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Task

• Page 256-7
• Summary questions 1 - 2

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18. Tests for positive ions

• Add sodium hydroxide (NaOH)
• Cu (II) light blue ppt
• Iron(II) dirty green ppt
• Iron(III) red/brown ppt
• Al, Ca, Mg white ppt
• Add more NaOH to Al/Ca/Mg
• Al white ppt dissolves again
• Ca, Mg white ppt does not dissolve
• Add NaOH to ammonium ions (NH4)
• Makes ammonia!
• Warm soln and use damp red litmus on gas turns
  blue

Element Flame Colour
Li Bright red
Na Golden yellow
K Lilac
Ca Brick red
Ba Green
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19. Tests for negative ions

• Carbonates (CO32-)
• - Add dilute acid makes CO2.
• - CO2 turns limewater cloudy/milky
• Copper carbonate turns green to black when heated
• Zinc carbonate turns white to yellow when heated
  (and kept hot!)
• Nitrates
• Add NaOH and warm it. If no ammonia detected add
  Al and test for ammonia again (damp red litmus
  blue)

• Sulphates
• Add hydrochloric acid and barium chloride.
• Makes white ppt (barium sulphate)
• Halides
• Add dilute nitric acid and silver nitrate.
• Cl ions white ppt
• Br ions cream ppt
• I ions yellow ppt

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20. Testing for organic substances

• Contain carbon
• Burn or char on heating
• You can detect CC double bond with bromine water
  (orange to colourless)
• COMBUSTION ANALYSIS allows you to determine the
  empirical formula of an organic substance.

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21. Instrumental Analysis

• Technology is awesome
• Highly accurate
• Quicker
• Enable small quantities to be analysed
• Technology has not so awesome
• Usually expensive
• Takes special training to use
• Gives results that can often be interpreted only
  by comparison with already available known
  specimens

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22. Instrumental analysis 2

• AAS atomic absorption spectroscopy, measures
  concentrations of metals in liquids
• Mass spectrometry compares masses of different
  atoms using magnets!
• UV visible spectroscopy
• NMR (nuclear magnetic resonance) spectroscopy
• Chromatography
• Gas-liquid separates compounds easily vaporised
• Gel permeation separates according to size of
  molecules
• Ion-exchange separates according to charge
• High performance liquid separates compounds in
  solution