analysis of compounds

• carbon is detected by heating the sample with cuo, carbon is oxidised to co2 which tested with lime what gives milky colour
• anhydrous cuso4 is white in colour, when water is added to it, it turns blue
• sample passed through cuo gives h2o which turns anhydrous CuSO4 blue
• for detection of elements other than carbon and hydrogen we use lassaignes test
• The other elements are covalently bonded to the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal.
• what is lassaignes test

   a small piece of Na metal is heated in a fusion tube with the organic compound. The principle is that, in doing so, Na converts all the elements present into ionic form.
• sodium fusion extract

  The formed ionic salts are extracted from the fused mass by boiling it with distilled water
• The extract is boiled with FeSO4 and acidified with concentrated H2SO4. The appearance of Prussian blue colour indicates the presence of nitrogen.
• during the test fir nitrogen, The acid helps in the oxidation of ferrous ions to ferric ions. The formation of ferriferous cyanide indicates the presence of nitrogen.
• feriferrocyanide

  Fe4[Fe(CN)6]3
• The extract is treated with sodium nitroprusside. The appearance of violet colour indicates the presence of sulphur
• The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide indicates the presence of sulphur.
• In case, nitrogen and sulphur both are present in an organic compound, sodium thiocyanate is formed. It gives blood red colour and no Prussian blue since there are no free cyanide ions
• The sodium fusion extract is acidified with nitric acid and then treated with silver nitrate. A white precipitate, soluble in ammonium hydroxide shows the presence of chlorine, a yellowish precipitate, sparingly soluble in ammonium hydroxide shows the presence of bromine and a yellow precipitate, insoluble in ammonium hydroxide shows the presence of iodine.
• The compound is heated with an oxidising agent (sodium peroxide). The phosphorus present in the compound is oxidised to phosphate. The solution is boiled with nitric acid and then treated with ammonium molybdate. A yellow colouration or precipitate indicates the presence of phosphorus.
• liebig's method is used to estimate carbon and hydrogen by heating a known amount of organic molecules in the presence of pure oxygen, then collecting and weighing the carbon dioxide and water generated, and calculating percentages of carbon and hydrogen from the masses of carbon dioxide.
• A known mass of the compound is heated with CuO in an atmosphere of CO2, which yields free nitrogen along with CO2 and H2O. The gases are passed over a hot copper gauze to convert trace amounts of nitrogen oxides to N2. The gaseous mixture is collected over a solution of KOH, which absorbs CO2, and nitrogen is collected in the upper part of the graduated tube
• dumas method

  A) cuo gauze

  B) cuo and organic compound

  C) coarse cuo

  D) reduced copper gauze

  E) nitrogen

  F) co2

  G) mercury seal

  H) nitrometer

  
• how much c and h

  A) 12

  B) 44

  C) mass of co2 in compound

  D) 2

  E) mass of h2o in compound

  F) 18

  
• dumas method pt 2

  A) pressure of nitrogen

  B) volume of nitrogen collected

  C) aqueous tension

  D) 22400

  E) 28

  F) 28

  G) 22400xm

  
• kjeldals

  A) h2so4

  B) 14

  C) M

  D) 2(V-V1/2)

  E) 100/m

  
• • The compound containing nitrogen is heated with concentrated H2so4
  • Nitrogen in the compound gets converted to ammonium sulphate. The resulting acid mixture is then heated with excess of naoh which liberates nh3 gas which is further absorbed in a standard solution of h2so4
  • The amount of nh3 produced is determined by estimating the amount of h2so4 consumed in the reaction.
  • It is done by estimating unreacted sulphuric acid left by titrating with naoh
  • The difference between the initial amount of acid taken and that left after the reaction gives the amount of acid reacted with ammonia.
• Kjeldahl method is not applicable to compounds containing nitrogen in nitro and azo groups and nitrogen present in the ring (e.g. pyridine) as nitrogen of these compounds does not change to ammonium sulphate under these conditions.
• diagram

  A) kjeldahls trap

  B) compound and h2so4 and cuso4

  C) acid with known volume

  
• Carius method: A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as Carius tube, in a furnace. The halogen present forms the corresponding silver halide (AgX). It is filtered, washed, dried and weighed
• carius method \

  A) atomic mass of x

  B) atomic mass of x

  C) mass of agx obtained

  
• A known mass of an organic compound is heated in a Carius tube with sodium peroxide or fuming nitric acid. Sulphur present in the compound is oxidised to sulphuric acid. It is precipitated as barium sulphate by adding excess of barium chloride solution in water. The precipitate is filtered, washed, dried and weighed. The percentage of sulphur can be calculated from the mass of barium sulphate.
• A known mass of an organic compound is heated with fuming nitric acid whereupon phosphorus present in the compound is oxidised to phosphoric acid. It is precipitated as ammonium phosphomolybdate, (NH4) 3 PO4.12MoO3, by adding ammonia and ammonium molybdate. Alternatively, phosphoric acid may be precipitated as MgNH4PO4 by adding magnesia mixture which on ignition yields Mg2P2O7.
• sulphur carius

  A) 32

  B) amount of baso4 formed

  C) 233

  
• In Lassaigne’s test, a blood red colouration indicates the presence of:


  Both nitrogen and sulphur