Chemistry 3a - AQA

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  • Created by: Han2812
  • Created on: 18-05-13 11:04

The Periodic Table

History of the Periodic Table

  • In the 1800's, scientist could only categorise elements on: their physical and chemical properties, their Relative Atomic Mass
  • Newland's Law of Octaves was the first attempt to categorise elements in 1864 - noticed that every 8th element had similar properties, so ordered them in rows of 7
  • This broke down in the transition metals, as he left no gaps, mixed up non-metals and metals
  • Mendeleev in 1869 did leave gaps, and predicted new elements, ordering his periodic table in atomic mass like Newland, and element in groups with similar properties in groups

The Modern Periodic Table

  • The modern periodic table is now arranged by the elements electroinic structure and atomic number
  • Apart from transition metals, elements in the same group have the same number of electrons in their outer shell
  • The group number is the same as the number of electrons in the elements outer shell eg.Group 6, 6 electron in their highest energy level
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Groups: 1, 7 and Transition Metal

Group 1 - Alkali Metals

  • - As you go down, they become more reactive, have a lower melting and boiling points
  • - They form ionic compounds with non-metals
  • - Reaction to water produces hydrogen gas

Group 7 - Halogens

  • - As you down, they become  less reactive, have a higher melting and boiling points
  • - They are non metals with coloured vapours which are all poisonous except Iodine; Flourine -> yellow gas, Chlorine -> dense green gas, Bromine -> red-brown volatile liquid, Iodine -> dark grey solid or purple vapour
  • - They form ionic bonds with metals
  • - More reactive halogens will displace less reactive ones

Transition Metals

  • - Properties: Good conductors of heat + electricity, shiny, strong, dense
  • - Colourful compounds, metals have more than one ion eg Fe2+, Fe3
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Hardness of Water

How is water made hard?

  • Water is made hard by the Mg2+ and Ca2+ ions in the water by the rain falling on types of rock eg. Limestone, chalk, gypsum which dissove magnesium sulfate and calcium sufate - soluble

What are the problems of hard water?

  • Hard water produces scum which is insoluble when using a soapless detergent - so need to spend more money on soap in hard water areas, soft water makes a nice lather with soap
  • When heated, hard water also form scale (calcium carbonate) on heating elements- reduces efficency, longer to boil, maybe need to be replaced, can also block pipes - cost alot of money

Good Points:

  • Ca2+ ions are good for teath and bones
  • Less risk of developing heart disease in hard water areas than soft water areas

Tempory hardness --> caused by hydrogencarbonate

Permanent hardness --> caused by calcium sulfate

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Water Quality

  • Drinking water needs to be good quality
  • It needs to be free from poisonous salts like nitrates and harmful microbes

Water Treatment From Reserviors:

  • Water passes through a mesh screen - removes twigs and big bits
  • Chemicals are then added to make solids and microbes stick together and fall to the bottom
  • Water is filtered through gravel beds to remove solids
  • Water is then chlorinated to kill off any harmful microbes left - then sent to peoples houses

Some people buy water softeners which contain ion exchange resins - forms a precipitate with calcium carbonate, softens the water removing the Ca/Mg ions, sodium ions in the system replaces the Ca/Mg ions.

Advantages:

  • Flourine reduces tooth decay, chlorine prevents diseases

Disadvantages:

  • Can increase certain cancers, bone problems, clorine can react with natural substances in the water to produce toxin by-products
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Reversible Reactions + The Haber Process

A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants    A + B <=======> C + D

  • If a reversible reatcion takes place in a closed system, it will reach a state of equilibrium
  • The energy change in the forward direction is the same as in the reverse, but in the oposite direction eg: EXOTHERMIC in one direction, ENDOTHERMIC in the other
  • DYNAMIC EQUILBRIUM is the rate of the forward and reverse reactions are equal, no overall change, but the reaction hasnt stopped

Changing the temperature and pressure will give you more product

The Haber Process

  • Conditions: 200 atmosphere (pressure), 450 temperature, iron catalyst
  • N2 + 3H2 <======> 2NH3       Nitrogen + 3Hydrogen <======> Ammonia
  • The unused hydrogen and nitrogen are recycled
  • Iron catalyst is used to make the reaction go faster, which gets the equilbrium proportions faster, without affecting the position if the equilibrium (eg. % of the yield)
  • Without the catalyst, the temperature would have to be raised further, lowering the % of the yield
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Alcohols + Carboxylic Acids

Alcohols:

  • Have the '-OH' functional group, and end in 'ol' with the general formula CnH2n+1OH
  • The first three in the homologous series is Methanol, Ethanol, Propanol
  • They are flammable, first three dissolve completely in water to form neutral solutions, they also react with sodium to produce hydrogen and alkoxides
  • They are used in solvents - dissolve substances water cant eg. hydrocarbons, fats, oils. Also used as fuels - cars, sprit burners, made by sugar cane, ethanal is used in alcohol

Carboxylic Acids:

  • Have the '-COOH' functional group and end in 'anoic acid' (and start with 'meth/eth/prop)
  • They react like other acids with carbonates to produce carbon dioxide and salts that end in 'anoate'
  • They dissolve in water to produce acidic soloutions, but form weak acidic solutions because of the H+ ions released, so have a higher pH level (less acidic)
  • Ethanoic acid can be dissolved in water to make vinegar, citric acid is in oranges and lemons
  • Carboxylic acids are used to make soaps and detergents, also are mixed with alcohols to make esters
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Esters

Esters:

  • They are a mix of alcohol and carboxylic acid
  • Have the functional group '-COO-', names end in 'oate' with the alcohol forming the first part of the name and the carboxylic acid forming the second part - produce water as a by product

Properties:

  • Many esters have nice smells - sweet and fruity, also volitile - makes them perfect for perfumes
  • Flammable so the volitility makes them dangerous
  • They DON'T mix well with water but DO mix well with alcohols and organic substances

Uses:

  • Perfumes
  • Flavourings and aromas
  • Ointments
  • Solvents
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