National Chemistry

These notes are for the Scottish National Chemistry course taught in fourth year in most Scottish schools.

The notes available here are concise notes. They are NOT to be considered as material to learn from - they are for revision.

 The notes are arranged under the following topics

National 3 Unit 1
Unit 2
Unit 3

National 4 and 5 Unit 1 Rates of Reaction
Atomic Structure
Bonding and Properties
Acids and bases

National 4 and 5 Unit 2 Fuels and Homologous Series
Consumer Products
Carbohydrates

National 4 and 5 Unit 3 Metals
Plastics
Fertilisers
Nuclear Chemistry
Chemical analysis

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National 4 and 5 Fertilisers

Fertilisers

  Increased world population has led to the need for more efficient food production.
  Growing plants require nutrients (from compounds of K, P and N). Fertilisers are substances which restore the essential elements for plant growth to the soil.

Useful fertilisers - because they are soluble and contain essential elements are ammonium
salts, potassium salts, nitrates and phosphates. Ammonia and nitric acid are important
compounds in the manufacture of fertilisers. Different crops need different fertilisers containing different amounts of potassium, nitrogen and phosphorous.

 Nitrogen can be put into the soil naturally by
  (i) decomposition of plant and animal protein (remains)
  (ii) nitrifying bacteria in root nodules of some plants convert atmosphere (free) N2(g) into nitrogen compounds

  In the nitrogen cycle plants obtain nitrogen from the soil while dead plants and animals replace the nitrogen by decomposition. However, the harvesting of food removes the chance of nitrogen returning to the soil naturally.

HABER PROCESS - manufactures ammonia
                                            Iron catalys ; 400oC
  NITROGEN+HYDROGEN ----------------------> AMMONIA
                                           HIGH PRESSURE

N2 + 3H2 <------- 2NH3

The Haber process is one of the most important reactions in the production of fertilisers and is an example of a reversible reaction. That is; as the nitrogen and hydrogen make ammonia, the ammonia in turn breaks down to hydrogen and nitrogen. The proportions of each that exist depends on carefully controlled reaction conditions

Ammonia is used to produce nitric acid which is then used to make nitrate compounds (eg ammonium nitrate).

NH3 -------- HNO3 ------neutralisation-- NH4NO3

  Ammonia gas (NH3) is colourless, soluble, has a characteristic smell and is an alkaline (pH7) gas (pH paper = blue). Ammonia is used to make ammonium compounds and to produce nitric acid. The Haber process is carried out at a moderately high temperature to ensure a faster (though less) yield of ammonia. (film)

Ammonia can be prepared in a lab by heating an ammonium compound with sodium hydroxide
 (this is similar to acid + alkali - it forms salt + water as well as ammonia
  NH4Cl + NaOH -----> NaCl + H2O + NH3

Nitrogen gas is not very reactive and will only react with oxygen in the presence of a great deal of energy (eg from a lightning storm or in a car engine) - therefore to produce the brown nitrogen dioxide (NO2)by reacting nitrogen and oxygen is very expensive.
  When NO2 is present in the air it dissolves to produce nitric acid (acid rain) which helps replace nitrogen in the soil but also lowers the pH (makes acidic).

  Industrially nitrogen dioxide is produced by oxidising ammonia in the presence of a catalyst - part of the OSWALD process to produce nitric acid.

  N2 + 3H2 ------ > NH3         Haber produced ammonia

  NH3 + O2 ------ > NO2         Oswald produces nitrogen dioxide

Heat is used to start this reaction but does not need to be supplied once reaction has started as the reaction supplies its own heat - is exothermic

  NO2 + H2O ----in the air----> HNO3         (Nitric acid produced in air = acid rain)

In the lab oxidation of ammonia this is carried out hsing hot platinium catalyst. This is heated at the start but does not need heated during the reaction as heat is given out which continues to make the platinum catalyst glow hot.

Haber uses an Iron catalyst while Oswald uses a Platinium catalyst
Rememeber by alphabetical order HI (Haber/Iron) and OP (Owald/Platinium)

 Calculate the percentage of an element in a compound
What is the percentage of nitrogen in NH4NO3 ?
step 1 : mass of 1 mole (2 x N) + (4 x H) + (3 x O)
  (2 x 14) + (4 x 1) + (3 x 16)
  28 + 4 +48 = 80g

step 2 : How much nitrogen is present ( 2 x N) = (2 x 14) = 28

step 3: 28g out of 80g is nitrogen ie  28
  80

step 4: remember it is a percentage: 28  x 100 =
  80

another example

 

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